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  • Other Sources  (213)
  • COMMUNICATIONS AND RADAR  (213)
  • 1985-1989  (213)
  • 1955-1959
  • 1985  (213)
  • 1
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    DSN frequency and timing system, Mark 4-85 (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: As part of the Deep Space Network (DSN) Mark IVA implementation program, the DSN frequency and timing system is currently undergoing changes. With the implementation of signal processing centers (SPC) at each deep space communications complex (DSCC), major changes to the frequency and timing distribution equipment were necessary. A functional description of the Mark IVA frequency and timing system (FTS) as it exists today and planned capabilities through 1988 is given.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Progr. Rept.; p 113-119
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  • 2
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    Use of ground radar to detect reentering debris (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The velocity of the particles is required to identify the type of particles producing the ionization trails. A method of approximating the velocity of a meteor from radar data was developed. The method requires the time between the spacings of the Fresnel interference fringes, the range to the ionization trail, and the wavelength of the radar system. The orbital mechanics of the problem are evaluated, if the particles originate with the shuttle, the orbital mechanics will substantiate the relative position of the particles with the position of the shuttle. A program to determine spacecraft orbital decay due to perturbations is utilized for a preliminary evaluation of the orbital mechanics of the problem. Many assumptions concerning the size, shape, density, etc. of the particles are necessary for the preliminary evaluation. The results do not negate the possibility that the events observed by the radar are reentering particles originating from the shuttle.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Orbital Debris; p 164-169
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  • 3
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    CV-990 L-band SAR: A calibration experiment (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: Calibrated image data is required by most users of synthetic aperture radar (SAR) data particularly those attempting to classify targets based upon their radar backscatter signature as a function of frequency polarization or incidence angle. In this experiment, the backscatter derived by calibrating the NASA/JPL CV-990 L-band SAR, and the backscatter reported from a pass of the NASA/JSC C-130 scatterometer as the two instruments flew over the same site at different times are compared.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA(JPL Aircraft SAR Workshop Proc.; p 17-20
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  • 4
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    Radar system description (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: A brief overview is given of the hardware and software utilized to generate the CV-990 synthetic aperture radar's image products. The on-board hardware is described, then the operational processing software, and finally the image products that are routinely available.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA(JPL Aircraft SAR Workshop Proc.; p 5-12
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  • 5
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    Improved mapping of radio sources from VLBI data by least-square fit (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: A method is described for producing improved mapping of radio sources from Very Long Base Interferometry (VLBI) data. The method described is more direct than existing Fourier methods, is often more accurate, and runs at least as fast. The visibility data is modeled here, as in existing methods, as a function of the unknown brightness distribution and the unknown antenna gains and phases. These unknowns are chosen so that the resulting function values are as near as possible to the observed values. If researchers use the radio mapping source deviation to measure the closeness of this fit to the observed values, they are led to the problem of minimizing a certain function of all the unknown parameters. This minimization problem cannot be solved directly, but it can be attacked by iterative methods which we show converge automatically to the minimum with no user intervention. The resulting brightness distribution will furnish the best fit to the data among all brightness distributions of given resolution.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Progr. Rept.; p 199-210
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  • 6
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    Comparison of the calibration of ionospheric delay in VLBI data by the methods of dual frequency and Faraday rotation (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: When both S-band and X-band data are recorded for a signal which has passed through the ionosphere, it is possible to calculate the ionospheric contribution to signal delay. In Very Long Baseline Interferometry (VLBI) this method is used to calibrate the ionosphere. In the absence of dual frequency data, the ionospheric content measured by Faraday rotation, using a signal from a geostationary satellite, is mapped to the VLBI observing direction. The purpose here is to compare the ionospheric delay obtained by these two methods. The principal conclusions are: (1) the correlation between delays obtained by these two methods is weak; (2) in mapping Faraday rotation measurements to the VLBI observing direction, a simple mapping algorithm which accounts only for changes in hour angle and elevation angle is better than a more elaborate algorithm which includes solar and geomagnetic effects; (3) fluctuations in the difference in total electron content as seen by two antennas defining a baseline limit the application of Faraday rotation data to VLBI.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Progr. Rept.; p 11-23
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  • 7
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    SETI radio spectrum surveillance system (1985)
    In:  CASI
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    Publication Date: 2006-02-14
    Description: The SETI Radio Spectrum Surveillance System (SRSSS) will provide a data base for assessing the radio frequency interference (RFI) environment for SETI and minimizing RFI disruptions during the search. The system's hardware and software are described and the sensitivity of the system is discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Progr. Rept.; p 173-184
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  • 8
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    Propagation and radiation characteristics of a multimode corrugated waveguide feedhorn (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: A prototype of the multimode corrugated feedhorn which will be used in the 400 kW CW Ka-band radar system is described. A rough design is done using coupled mode theory and standard corrugated waveguide modes. A more exact analysis using mode matching techniques is then used which takes into account the effect of a finite number of corrugations per wavelength and determines the modes which are reflected from the device. A prototype feedhorn has been constructed and measured. These experimental results are then compared to the theoretical predictions which agree satisfactorily closely.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Progr. Rept.; p 57-67
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  • 9
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    A VLBI survey at 2.29 GHz (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The Deep Space Network (DSN) is establishing a high-accuracy VLBI celestial reference frame. The results of a search for suitable radio sources to be used in constructing this frame are given. The VLBI observations using DSN baselines at 2.29 GHz with fringe spacings of about 3 milliarcseconds have been performed on 1398 radio sources spread over the entire sky. Of those, 917 sources were detected including 93% of the identifed BL Lacertae objects, 86% of Quasars and 36% of galaxies. The resulting catalog of compact radio sources is also useful for various astrophysical studies and in the formation of VLBI celestial reference frames.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Progr. Rept.; p 1-10
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  • 10
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    A new 70-meter antenna quadripod with reduced RF blockage (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The new subreflector mount (quadripod) for the 64-meter to 70-meter antenna extension project was the result of many trial designs aimed at reducing radio frequency spherical and plane wave blockage and minimizing structural weight while satisfying strength and natural frequency requirements. An optimum design emerged which has a gain improvement of 0.32 dB over the present 64-meter design. Some of the trial designs made and the final optimum configuration selected are described.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Progr. Rept.; p 24-30
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  • 11
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    16-QAM and trellis-coded 16-QAM on nonlinear channels (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The use of 16-QAM on bandlimited nonlinear satellite channels, in uncoded and trellis-coded form, for bandwidth efficient modulation (ideally 4 bps/Hz) is discussed. To avoid severe degradation due to AM/AM and AM/PM distortion, or to avoid the need for large back-off, predistorting the 16-QAM constellation at the modulator is considered. Performance for varying back-off settings for uncoded and coded 16-QAM is simulated, and it is found that the four-state trellis code has a coding gain of about 8 dB, larger than expected based on linear channel analysis, while the 16-state code gains only marginally beyond this.
    Keywords: COMMUNICATIONS AND RADAR
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  • 12
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    2400 bit/s DMSK modem for mobile satellite service (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The letter describes the implementation of a differentially coherent receiver suitable for bursty signal transmission over fading channels. To meet the severe system phase response requirement, this implementation is conducted at baseband. Means of frequency correction (AFC) is also shown. This receiver is simple and can easily be fabricated using VLSI technology.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Electronics Letters (ISSN 0013-5194); 21; 965
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  • 13
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    An optimized bandwidth efficient demand assigned protocol for integrated Mobile Satellite Services (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper describes the design of a demand assigned protocol based on bandwidth efficiency for integrated services of a Mobile Satellite System (MSS). An MSS provides data (closed-ended) and voice (open-ended) communications services for a large number of mobile users dispersed over a wide geographical area. Each mobile requests its desired service through a designated set of channels to a network management center. Either pure or slotted ALOHA random access scheme can be used to make connection requests, while data and voice communications are demand assigned. All channels have equal bandwidth and can be adaptively used for reservation requests, data connections or voice connections to maximize the bandwidth utilization. In this paper, perfect communications channels are assumed. It has been shown that, for the case considered, using the slotted ALOHA scheme for making connection requests can save about 30 percent on the total number of channels over using the pure ALHOA scheme.
    Keywords: COMMUNICATIONS AND RADAR
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  • 14
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    Further results on rate 1/N convolutional code constructions with minimum required SNR criterion (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: New good (K, 1/N) convolutional codes for 8 or = to K or = to 13 and 2 or = to N or = to 8 were found and tabulated which require minimum signal-to-noise ratio (SNR) for given desired bit error rates (BER) with Viterbi decoding. The transfer function bound was used for the BER evaluations. These low-rate codes are expected to have a number of applications, especially for systems having large bandwidth-bit time products such as deep space and spread spectrum communication systems.
    Keywords: COMMUNICATIONS AND RADAR
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  • 15
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    Land vehicle antennas for satellite mobile communications (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Antenna designs applicable to future satellite mobile vehicle communications are examined. Microstrip disk, quadrifilar helix, cylindrical microstrip, and inverted V and U crossed-dipole low gain antennas (3-5 dBic) that provide omnidirectional coverage are described. Diagrams of medium gain antenna (9-12 dBic) concepts are presented; the antennas are classified into three types: (1) electronically steered with digital phase shifters; (2) electronically switched with switchable power divider/combiner; and (3) mechanically steered with motor. The operating characteristics of a conformal antenna with electronic beam steering and a nonconformal design with mechanical steering are evaluated with respect to isolation levels in a multiple satellite system. Vehicle antenna pointing systems and antenna system costs are investigated.
    Keywords: COMMUNICATIONS AND RADAR
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  • 16
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    FH/MFSK performance in multitone jamming (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The performance of frequency-hopped (FH) M-ary frequency-shift keyed (MFSK) signals in partial-band noise as analyzed in the open literature. The previous research is extended to the usually more effective class of multitone jamming. Some objectives researched are: (1) To categorize several different multitone jamming strategies; (2) To analyze the performance of FH/MSFK signaling, both uncoded with diversity, assuming a noncoherent energy detection metric with linear combining and perfect jamming state side information, in the presence of worst case interference for each of these multitone categories; and (3) To compare the effectiveness of the various multitone jamming techniques, and contrast the results with the partial band noise jamming case.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Journal on Selected Areas in Communications (ISSN 0733-8716); SAC-3; 627-643
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  • 17
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    Erasure information for a Reed-Solomon decoder (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Many Reed-Solomon decoders, including the one decoding the outer code for Voyager data from Uranus, assume that all symbols have the same chance of being correct or incorrect. Insome cases, like in a burst of incorrect symbols, this is not the case, and a Reed-Solomon decoder could make use of this. The use of information about bit quality sent to the Reed-Solomon from an (inner) Viterbi decoder is examined, as well as information about the error status of adjacent symbols in decoding interleaved Reed-Solomon encoded symbols. It is discovered that, in a region of interest, only about 0.04 dB can gained.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 39-44
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  • 18
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    Decoding convolutionally encoded images (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Maximum Likelihood Convolutional Decoding, which is used by the Deep Space Network for short constraint-length convolutional codes, assumes that all strings of information bits are equally likely. In some cases, like image data, this is not the case. The use of information about an adjacent pixel in decoding convolutionally encoded Voyager images is examined. It is discovered that, in a region of interest, as much as 2 dB may be gained.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 34-38
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  • 19
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    In search of a 2-dB coding gain (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A recent code search found a (15,1/5), a (14,1/6), and a (15,1/6) convolutional code which, when concatenated with a 10-bit (1023,959) Reed-Solomon (RS) code, achieves a bit-error rate (BER) of 0.000001 at a bit signal-to-noise ratio (SNR) of 0.50 dB, 0.47 dB and 0.42 B, respectively. All of these three codes outperform the Voyager communication system, our baseline, which achieves a BER of 10.000001 at bit SNR of 2.53 db, by more than 2 dB. The 2 dB coding improvement goal was exceeded.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 26-33
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  • 20
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    The Spectrum Orbit Utilization Program (SOUP) used for DBS plan analysis at RARC '83 (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper describes the history, functions, and usage of the program that was used to analyze the plans for direct broadcast satellite service developed in the course of the 1983 Regional Administrative Radio Conference for ITU Region 2. Given the requirements for direct broadcast service by the administrations, the conference delegates (1) developed the appropriate technical parameters; (2) made tentative assignments to the orbit locations, frequencies, and polarizations of space stations, (3) calculated the interferences and margins of such assignments through the use of the Spectrum Orbit Utilization Program (SOUP); and (4) iterated this procedure until an acceptable plan was found.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Journal on Selected Areas in Communications (ISSN 0733-8716); SAC-3; 44-49
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  • 21
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    Experimental results supporting the determination of service quality objectives for DBS systems (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A summary of the results of a joint United States and Canadian program on subjective measurements of the picture degradation caused by noise and interference on an NTSC encoded color television signal is given in this paper. The effects of system noise, cochannel and adjacent channel interference, and both single entry and aggregate as well as a combination of these types of interference were subjectively evaluated by expert and nonexpert viewers under reference conditions. These results were used to develop the rationale used at RARC '83 to establish the service quality objective for planning the DBS service for the American continents.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Journal on Selected Areas in Communications (ISSN 0733-8716); SAC-3; 87-99
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  • 22
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    Birds and insects as radar targets - A review (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A review of radar cross-section measurements of birds and insects is presented. A brief discussion of some possible theoretical models is also given and comparisons made with the measurements. The comparisons suggest that most targets are, at present, better modeled by a prolate spheroid having a length-to-width ratio between 3 and 10 than by the often used equivalent weight water sphere. In addition, many targets observed with linear horizontal polarization have maximum cross sections much better estimated by a resonant half-wave dipole than by a water sphere. Also considered are birds and insects in the aggregate as a local radar 'clutter' source. Order-of-magnitude estimates are given for many reasonable target number densities. These estimates are then used to predict X-band volume reflectivities. Other topics that are of interest to the radar engineer are discussed, including the doppler bandwidth due to the internal motions of a single bird, the radar cross-section probability densities of single birds and insects, the variability of the functional form of the probability density functions, and the Fourier spectra of single birds and insects.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE, Proceedings (ISSN 0018-9219); 73; 205-227
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  • 23
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    Convolutional coding combined with continuous phase modulation (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Background theory and specific coding designs for combined coding/modulation schemes utilizing convolutional codes and continuous-phase modulation (CPM) are presented. In this paper the case of r = 1/2 coding onto a 4-ary CPM is emphasized, with short-constraint length codes presented for continuous-phase FSK, double-raised-cosine, and triple-raised-cosine modulation. Coding buys several decibels of coding gain over the Gaussian channel, with an attendant increase of bandwidth. Performance comparisons in the power-bandwidth tradeoff with other approaches are made.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-33; 20-29
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  • 24
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    Spread spectrum communications. Volume 1, 2 & 3 (1985)
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    Publication Date: 2011-08-19
    Description: The design and operation of spread-spectrum (SS) communication systems are examined in an introductory text intended for graduate engineering students and practicing engineers. Chapters are devoted to an overview of SS systems, the historical origins of SS, basic concepts and system models, antijam communication systems, pseudonoise generators, coherent direct-sequence systems, noncoherent frequency-hopped systems, coherent and differentially coherent modulation techniques, pseudonoise acquisition and tracking in direct-sequence receivers, time and frequency synchronization of frequency-hopped receivers, low-probability-of-intercept communication, and multiple-access communication. Graphs, diagrams, and photographs are provided.
    Keywords: COMMUNICATIONS AND RADAR
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  • 25
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    A retransmission protocol for the message service of a land mobile satellite experiment (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The objectives of NASA's land mobile satellite experiments are discussed. The assigned multiple access protocol combined with a retransmission scheme is to provide reliable transmission of data messages from mobiles to base stations (BSs). The sequences for communication between mobiles and BSs, mobiles and the network management center (NMC), and BSs and NMC are examined, and an example of mobiles/BSs communication is provided. The performance of the retransmission protocol and data message reservation and message channels delays are analyzed. A bit error rate of 0.001 is observed for satellite channels in a mobile environment and the message error probability is between 0-0.1.
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  • 26
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    Generation, modulation and reception of orthogonally polarized signals (1985)
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    Publication Date: 2011-08-19
    Description: The radiating electromagnetic field of a dipole antenna is considered. By allowing the dipole to rotate about its midpoint, one can construct an entire set of signal polarizations wherein distinct members of the set are mutually orthogonal. It is shown how these signals can be modulated and demodulated to convey information. These ideas are then generalized, and both balanced, as well as unbalanced quadrapole modulations are defined. Methods of receiver synchronization to such signals are described, as well as their potential application to multiple access and anti-jam communications.
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  • 27
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    An adaptive quantization method for burst mode synthetic aperture radar data (1985)
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    Publication Date: 2011-08-19
    Description: Synthetic aperture radar (SAR) has high data rate because it collects and processes the data coherently. The data rate limitation of the system has to be satisfied while maintaining good image quality. Thus, a quantizer with minimum data rate and high SNR should be employed. An adaptive quantization method is proposed for the burst mode SAR. This adaptive quantizer uses uniformly quantized data to select a subset of bits which is equivalent to changing the step size of the uniform quantizer. A simple implementation which uses the previous burst data to compute the local statistics for the bit selection is presented. The use of previous burst simplifies the implementation because it does not require storage or delay; however, an abrupt change in the terrain could result in incorrect bit selection. An error analysis of this implementation and comparison of two burst mode SAR images formed using the uniformly quantized and adaptively quantized data is presented.
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  • 28
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    Analysis of elliptical and circular microstrip antennas using moment method (1985)
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    Publication Date: 2011-08-19
    Description: A method of calculating the input impedance of either a circular or a slightly elliptical microstrip antenna excited by a coaxial probe is presented. Using the reaction integral equation and the exact dyadic Green's function, the finite substrate thickness is taken into account in the formulation. Good agreement with experimental results for an elliptical patch is obtained and a design procedure for a circularly polarized antenna is presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-33; 954-959
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  • 29
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    On the probability density function of the squared envelope of a sum of random phase vectors (1985)
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    Publication Date: 2011-08-19
    Description: Weber et al. (1980) have found that a generic problem arises in the study of multiuser FHMA/MFSK systems. According to this problem, the presence of the other channel users acts as interference to reception of the desired user's transmission. The present investigation is concerned with a recursive solution in which the recursion parameter is the number of vectors in the sum. A mathematical characterization of such a solution is presented, taking into account the simple two-vector case in which a well-known closed form result is possible. Some numerical results are also discussed. It is pointed out that the considered recursive solution provides a break in the bottleneck associated with the exact computation of the error probability performance of multiuser FHMA/MFSK systems and single access MFSK systems corrupted by multitone jamming.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-33; 993-996
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  • 30
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    Comments on 'A technique for improving the efficiency of M-ary signaling' (1985)
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    Publication Date: 2011-08-19
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-33; 877
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  • 31
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    Performance of a normalized energy metric without jammer state information for an FH/MFSK system in worst case partial band jamming (1985)
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    Publication Date: 2011-08-19
    Description: For a frequency-hopped noncoherent MFSK communication system without jammer state information (JSI) in a worst case partial band jamming environment, it is well known that the use of a conventional unquantized metric results in very poor performance. In this paper, a 'normalized' unquantized energy metric is suggested for such a system. It is shown that with this metric, one can save 2-3 dB in required signal energy over the system with hard decision metric without JSI for the same desired performance. When this very robust metric is compared to the conventional unquantized energy metric with JSI, the loss in required signal energy is shown to be small. Thus, the use of this normalized metric provides performance comparable to systems for which JSI is known. Cutoff rate and bit error rate with dual-k coding are used for the performance measures.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-33; 869-877
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    Double symbol error rates for differential detection of narrow-band FM (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper evaluates the double symbol error rate (average probability of two consecutive symbol errors) in differentially detected narrow-band FM. Numerical results are presented for the special case of MSK with a Gaussian IF receive filter. It is shown that, not unlike similar results previously obtained for the single error probability of such systems, large inaccuracies in predicted performance can occur when intersymbol interference is ignored.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-33; 394-398
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  • 33
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    Dual-band reactively loaded microstrip antenna (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A previously derived theory is applied to a microstrip antenna with a reactive load to produce a dual-band radiator. A model consisting of a rectangular patch radiator loaded with a variable length short-circuited coaxial stub was investigated experimentally. Comparisons of theoretical predictions and experimental data are made for the impedance and resonant frequencies as a function of the position of the load, the length of the stub, and the characteristic impedance of the stub.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-33; 556-561
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  • 34
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    VLBI collimation-tower technique for time-delay studies of a large ground-station communications antenna (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A need for an accurate but inexpensive method for measuring and evaluating time delays of large ground antennas for VLBI applications motivated the development of the collimation tower technique. Supporting analytical work which was performed primarily to verify time delay measurement results obtained for a large antenna when the transmitter was at a collimation distance of 1/25 of the usual far field criterion is discussed. Comparisons of theoretical and experimental results are also given.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-33; 549-556
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    Development and use of the computer software package for planning the 12 GHz broadcasting-satellite service at RARC '83 (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The 1983 Regional Administrative Radio Conference (RARC '83) had mainly the objective to draw up a plan of detailed frequency assignments and orbital positions for the 12 GHz broadcasting-satellite service (BSS) in ITU Region 2 (the Western Hemisphere) and associated feeder links (earth-to-space) in the 17 GHz band. It was found that for RARC '83 new planning methods and procedures would be needed. The new requirements made it necessary to develop a new generation of planning software. Attention is given to the development of the computer programs to be used at the conference, the package of computer programs, and the use of the computer programs.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Journal on Selected Areas in Communications (ISSN 0733-8716); SAC-3; 36-43
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  • 36
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    New short constraint length, rate 1/N convolutional codes which minimize the required SNR for given desired bit error rates (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: It is pointed out that for a convolutional coding system, the Bit Error Rate (BER) at the Viterbi decoder output is upper-bounded by the transfer function bound. A large number of rate 1/N convolutional codes have been reported. The criteria used for determining the quality of a code in code search procedures, however, may not be very suited for cases in which the required BER is in the moderate range. For this reason, it may be best to select the code with the aim to minimize the required SNR for a given disired BER. Partial code searching techniques are presented, and a table listing the code search results is provided.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-33; 171-177
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    Vector diffraction analysis of reflector antennas with mesh surfaces (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Reflector antennas with mesh surfaces are used extensively in many satellite and ground antenna systems. A strip-aperture modeling of commonly used mesh surfaces is presented which provides considerable versatility in characterizing the mesh cells. The mesh transmission coefficients are constructed using a Floquet-modal expansion in conjuction with two dominant aperture modes. To account for the mesh local coordinates, the Eulerian angle transformation is invoked to obtain the total induced current on the curved reflector surface. General formulas are presented to show how the solid surface induced current is modified due to the transmission through the mesh. The effects of a variety of mesh configurations on both the co-polar and cross-polar patterns of reflector antennas are studied by numerically evaluating the vector diffraction integral using the Jacobi-Bessel expansion. For some special cases, a comparison is made with the results of the commonly used wire-grid formulation. Many of the numerical data are tailored to the dimensions of a conceptually designed mesh deployable offset reflector of the land mobile satellite system (LMSS).
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-33; 76-90
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  • 38
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    Discharge pulse phenomenology (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A model was developed which places radiation induced discharge pulse results into a unified conceptual framework. Only two phenomena are required to interpret all space and laboratory results: (1) radiation produces large electrostatic fields inside insulators via the trapping of a net space charge density; and (2) the electrostatic fields initiate discharge streamer plasmas similar to those investigated in high voltage electrical insulation materials; these streamer plasmas generate the pulsing phenomena. The apparent variability and diversity of results seen is an inherent feature of the plasma streamer mechanism acting in the electric fields which is created by irradiation of the dielectrics. The implications of the model are extensive and lead to constraints over what can be done about spacecraft pulsing.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Lewis Research Center Spacecraft Environ. Interactions Technol., 1983; p 483-509
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  • 39
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    Characteristics of EMI generated by negative metal-positive dielectric voltage stresses due to spacecraft charging (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Charging of spacecraft surfaces by the environmental plasma can result in differential potentials between metallic structure and adjacent dielectric surfaces in which the relative polarity of the voltage stress is either negative dielectric/positive metal or negative metal/positive dielectric. Negative metal/positive dielectric is a stress condition that may arise if relatively large areas of spacecraft surface metals are shadowed from solar UV and/or if the UV intensity is reduced as in the situation in which the spacecraft is entering into or leaving eclipse. The results of experimental studies of negative metal/positive dielectric systems are given. Information is given on: enhanced electron emission I-V curves; e(3) corona noise vs e(3) steady-state current; the localized nature of e(3) and negative metal arc discharge currents; negative metal arc discharges at stress thresholds below 1 kilovolt; negative metal arc discharge characteristics; dependence of blowoff arc discharge current on spacecraft capacitance to space (linear dimension); and damage to second surface mirrors due to negative metal arcs.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Lewis Research Center Spacecraft Environ. Interactions Technol., 1983; p 437-452
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  • 40
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    Novel applications of the NASA/GSFC Viterbi decoder hardware simulator (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The NASA/GSFC developed an all digital, real time, programmable Viterbi decoder simulator operating at rates up to 6 Msps. With this simulator, the bit error rate (BER) performance of convolutionally encoded/Viterbi decoded Shuttle-TDRSS return link channels under pulsed radio frequency interference (RFI) conditions has been predicted. The principles of the simulator are described with special emphasis on the channel simulator and the essential interaction between CLASS software and the simulator. The sensitivity of coded BER as function of several illustrative RFI parameters is discussed for two typical Shuttle-TDRSS return link configurations.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Johnson Space Center Space Shuttle Tech. Conf., Pt. 2; p 821-830
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    Electronics systems test laboratory testing of shuttle communications systems (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Shuttle communications and tracking systems space to space and space to ground compatibility and performance evaluations are conducted in the NASA Johnson Space Center Electronics Systems Test Laboratory (ESTL). This evaluation is accomplished through systems verification/certification tests using orbiter communications hardware in conjunction with other shuttle communications and tracking external elements to evaluate end to end system compatibility and to verify/certify that overall system performance meets program requirements before manned flight usage. In this role, the ESTL serves as a multielement major ground test facility. The ESTL capability and program concept are discussed. The system test philosophy for the complex communications channels is described in terms of the major phases. Results of space to space and space to ground systems tests are presented. Several examples of the ESTL's unique capabilities to locate and help resolve potential problems are discussed in detail.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Space Shuttle Tech. Conf., Pt. 2; p 831-849
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  • 42
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    The Communications link analysis and simulation system (CLASS) (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The Communications Link Analysis and Simulation System (CLASS) is a comprehensive, computerized communications and tracking system analysis tool under development by the Networks Directorate of the NASA/GSFC. The primary use of this system is to provide the capability to predict the performance of the Tracking and Data Relay Satellite system (TDRSS) User Communications and Tracking links through the TDRSS. The general capabilities and operational philosophy of the current and final versions of the CLASS are described along with some examples of analyses which have been performed utilizing the capabilities of this system.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Johnson Space Center Space Shuttle Tech. Conf., Pt. 2; p 787-797
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    Shuttle payload S-band communications system (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The Shuttle payload S-band communications system design, operational capabilities, and performance are described in detail. System design requirements, overall system and configuration and operation, and laboratory/flight test results are presented. Payload communications requirements development is discussed in terms of evolvement of requirements as well as the resulting technical challenges encountered in meeting the initial requirements. Initial design approaches are described along with cost-saving initiatives that subsequently had to be made. The resulting system implementation that was finally adopted is presented along with a functional description of the system operation. A description of system test results, problems encountered, how the problems were solved, and the system flight experience to date is presented. Finally, a summary of the advancements made and the lessons learned is discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Space Shuttle Tech. Conf., Pt. 2; p 767-776
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    TDRSS S-shuttle unique receiver equipment (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Beginning with STS-9, the Tracking and Date Relay Satellite system (TDRSS) will start providing S- and Ku-band communications and tracking support to the Space Shuttle and its payloads. The most significant element of this support takes place at the TDRSS White Sands Ground Terminal, which processes the Shuttle return link S- and Ku-band signals. While Ku-band hardware available to other TDRSS users is also applied to Ku-Shuttle, stringent S-Shuttle link margins have precluded the application of the standard TDRSS S-band processing equipment to S-Shuttle. It was therfore found necessary to develop a unique S-Shuttle Receiver that embodies state-of-the-art digital technology and processing techniques. This receiver, developed by Motorola, Inc., enhances link margins by 1.5 dB relative to the standard S-band equipment and its bit error rate performance is within a few tenths of a dB of theory. An overview description of the Space Shuttle Receiver Equipment (SSRE) is presented which includes the presentation of block diagrams and salient design features. Selected, measured performance results are also presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Johnson Space Center Space Shuttle Tech. Conf., Pt. 2; p 777-786
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  • 45
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    Shuttle ku-band communications/radar technical concepts (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Technical data on the Shuttle Orbiter K sub u-band communications/radar system are presented. The more challenging aspects of the system design and development are emphasized. The technical problems encountered and the advancements made in solving them are discussed. The radar functions are presented first. Requirements and design/implementation approaches are discussed. Advanced features are explained, including Doppler measurement, frequency diversity, multiple pulse repetition frequencies and pulse widths, and multiple modes. The communications functions that are presented include advances made because of the requirements for multiple communications modes. Spread spectrum, quadrature phase shift keying (QPSK), variable bit rates, and other advanced techniques are discussed. Performance results and conclusions reached are outlined.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Space Shuttle Tech. Conf., Pt. 2; p 757-766
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  • 46
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    Shuttle S-band communications technical concepts (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Using the S-band communications system, shuttle orbiter can communicate directly with the Earth via the Ground Spaceflight Tracking and Data Network (GSTDN) or via the Tracking and Data Relay Satellite System (TDRSS). The S-band frequencies provide the primary links for direct Earth and TDRSS communications during all launch and entry/landing phases of shuttle missions. On orbit, S-band links are used when TDRSS Ku-band is not available, when conditions require orbiter attitudes unfavorable to Ku-band communications, or when the payload bay doors are closed. the S-band communications functional requirements, the orbiter hardware configuration, and the NASA S-band communications network are described. The requirements and implementation concepts which resulted in techniques for shuttle S-band hardware development discussed include: (1) digital voice delta modulation; (2) convolutional coding/Viterbi decoding; (3) critical modulation index for phase modulation using a Costas loop (phase-shift keying) receiver; (4) optimum digital data modulation parameters for continuous-wave frequency modulation; (5) intermodulation effects of subcarrier ranging and time-division multiplexing data channels; (6) radiofrequency coverage; and (7) despreading techniques under poor signal-to-noise conditions. Channel performance is reviewed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Space Shuttle Tech. Conf., Pt. 2; p 720-756
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  • 47
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    DSN 34-meter Antenna Optics Analysis for Wideband SETI Investigations (1985)
    In:  CASI
    Details
    Publication Date: 2014-09-18
    Description: A DSN 34-meter symmetric Cassegrain antenna configuration is examined for wideband use over the frequency range of 1 to 10 GHz, rather than only at the narrow-band operational design frequencies of 2.295 GHz (S-band) and 8.448 GHz (X-band). Aperture efficiency and surface efficiency are calculated as the components determining the gain of the antenna. Noise temperature contributions arise from the ground, atmosphere, and quadripod scattering. These components are calculated as a function of frequency elevation angle to determine a G/T (gain/system noise temperature) figure-of-merit for a nominal 34-meter antenna configuration. A computational method was developed which will enable design of a multi-horn antenna feed system to optimally cover the 1 to 10 GHz frequency range.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 202-219
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  • 48
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    Performance of the Dsa's Subcarrier Demodulation Digital Loop (1985)
    In:  CASI
    Details
    Publication Date: 2014-09-18
    Description: The subcarrier demodulation digital loop is part of the baseband assembly. The subcarrier demodulator is a fourth-order Costas-type loop corresponding to a type 2 analog loop in terms of steady state response. The expected value and the variance of the error signal are determined as functions of the input SNR. A Nyquist sampling rate of the input signal is assumed. From the integro-difference equations a mixed s/z domain block diagram is obtained. From the loop's transfer function a set of gains for the loop filter is obtained. Also, a set of state equations is presented for future reference. Finally, the noise-equivalent bandwidths are calculated for normalized computation times of 0, 0.25 and 0.5. The subcarrier demodulator analyzed tracks a parabolic phase input with finite steady state error. Since at each update instant the loop gains are adjusted to compensate for the variations in SNR of the input signal, the noise-equivalent bandwidth is maintained constant.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 180-194
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  • 49
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    Reed-solomon Code Synchronization Revisited (1985)
    In:  CASI
    Details
    Publication Date: 2014-09-18
    Description: A concatenated coding consisting of an inner (7, 1/2) convolutional code and an outer (255, 223) Reed-Solomon code was recommended by the Consultative Committee for Space Data Systems for cross-supported space missions. The Reed-Solomon code that was chosen makes use of the Berlekamp encoding algorithm. Some peculiarities of this code that could give rise to synchronization problems are examined. Suggestions are given to alleviate these problems.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 91-96
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    Further Results on Rate 1/N Convolutional Code Constructions with Minimum Required SNR Criterion (1985)
    In:  CASI
    Details
    Publication Date: 2014-09-18
    Description: New good (K, 1/N) convolutional codes for 8 or = to K or = to 13 and 2 or = to N or = to 8 were found and tabulated which require minimum signal-to-noise ratio (SNR) for given desired bit error rates (BER) with Viterbi decoding. The transfer function bound was used for the BER evaluations. These low-rate codes are expected to have a number of applications, especially for systems having large bandwidth-bit time products such as deep space and spread spectrum communication systems.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 97-102
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    Microwave Surface Resistivity of Several Materials at Ambient Temperature (1985)
    In:  CASI
    Details
    Publication Date: 2014-09-18
    Description: Microwave surface resistivity of a number of metal and other sample materials was measured at X-band, approximately 8400 MHz. The method of measurement uses a TE sub 011 mode circular waveguide cavity resonator wherein the sample is used as one end of the cavity. This method has been used previously in JPL work with good results. Microwave reflection loss and noise arising from the dissipative loss are given, for materials having negligible transmission leakage.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 8-11
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    A Software Simulation Study of a Sequential Decoder Using the Fano Algorithm (1985)
    In:  CASI
    Details
    Publication Date: 2014-08-26
    Description: A set of subroutines was developed to simulate the performance of a sequential decoder based on the Fano algorithm. This simulation can be used to verify the coding performance of the International Cometary Explorer (ICE) communication link. The probability of frame deletion can be measured as a function of the number of computations allowed per frame and of E(b)/N(o). Both hard and soft quantized inputs are considered.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. Data Acquisition Rept.; p 40-41
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    Relating the Planetary Ephemerides and the Radio Reference Frame (1985)
    In:  CASI
    Details
    Publication Date: 2014-08-26
    Description: The positions of Venus, Mars, and Jupiter were obtained in the VLBI radio reference frame by measuring the position of a satellite (natural or artificial) of each planet relative to an extragalactic source in the radio catalogue. From the results for Mars and Venus it is concluded that the offset in right ascension of the radio frame from the dynamical equinox defined in DE200 is 0.00 sec +/- 0.04 sec. The observations for Jupiter imply a correction to its position from DE200 of -0.18 sec +/- 0.04 sec in right ascension and -0.06 +/- 0.05 sec in declination on 1983 April 29. The right ascension of Jupiter relative to the inner planets has been measured independently using Doppler tracking data near Jupiter encounter from Pioneers 10 and 11 and from Voyagers 1 and 2 by tying the tracking station positions, through previous spacecraft missions, to the DE200 ephemerides of the inner planets. This technique yielded a correction to Jupiter's right ascension of -0.22 +/- 0.05 sec, in good agreement with the results from the direct radio measurements.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. Data Acquisition Rept.; p 1-8
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    Symbol Stream Combining in a Convolutionally Coded System (1985)
    In:  CASI
    Details
    Publication Date: 2014-08-27
    Description: Symbol stream combining has been proposed as a method for arraying signals received at different antennas. If convolutional coding and Viterbi decoding are used, it is shown that a Viterbi decoder based on the proposed weighted sum of symbol streams yields maximum likelihood decisions.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. Data Acquisition Rept.; p 47-50
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    Synchronizing Heavily Encoded Data in Bad Weather (1985)
    In:  CASI
    Details
    Publication Date: 2014-08-26
    Description: Deep space missions choose a data rate to ensure reliable communication under most conditions. Certain critical data can be more heavily encoded, to be decoded under particularly bad atmospheric conditions. It is shown that, in such a system, finding and synchronizing critical data will not be a problem.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. Data Acquisition Rept.; p 38-39
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    Bit Error Rate of Coherent M-ary PSK (1985)
    In:  CASI
    Details
    Publication Date: 2014-08-26
    Description: The bit error rate (BER) for the coherent detection of M-ary PSK signals with Gray code bit mapping is considered. A closed-form expression for the exact BER of M-ary PSK is presented. Tight upper and lower bounds on BER are also obtained for M-ary PSK with larger M.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. Data Acquisition Rept.; p 31-37
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    Thin Route Project (1985)
    In:  CASI
    Details
    Publication Date: 2014-08-26
    Description: An overview of NASA efforts to improve on the number of carriers for satellite communication systems is presented. A brief history of satellite telecommunication systems and their use in linking underdeveloped areas, along with a brief explanation of the necessary hardware is also given.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA Ames Summer High School Apprenticeship Res. Program; p 47-51
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    Lack of Communication (1985)
    In:  CASI
    Details
    Publication Date: 2014-08-23
    Description: Attempts at establishing dependable lines of communication with isolated third world nations are outlined. INTELSAT as well as the Application Technology Satellites systems are mentioned. A prototype system called Thin Route is proposed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA Ames Summer High School Apprenticeship Res. Program; p 5-6
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    Strategies for FH/MFSK signaling with diversity in worst-case partial-band noise (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Optimum diversity and worst-case partial-band noise jamming conditions have been derived for noncoherent energy detection of frequency-hopped (FH) M-ary frequency-shift keyed (MFSK) signals using a soft-chip decision suboptimum linear combining metric with perfect jamming-state side information. However, the assumption implicit in previous publications is that the error is first maximized over the jammer's partial-band duty factor for arbitrary diversity, and the result is then minimized over the amount of diversity. This paper shows that if the order of optimization is reversed, different conditions and performance are produced; that is, the previous solution is not a saddlepoint. This introduces some game-theoretic considerations for the communicator and the jammer, the risks and advantages of which are explored.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Journal on Selected Areas in Communications (ISSN 0733-8716); SAC-3; 622-626
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    Propagation considerations in land mobile satellite transmission (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It appears likely that the Land Mobile Satellite Services (LMSS) will be authorized by the FCC for operation in the 800 to 900 MHz (UHF) and possibly near 1500 MHz (L-band). Propagation problems are clearly an important factor in the effectiveness of this service, but useful measurements are few, and produced contradictory interpretations. A first order overview of existing measurements is presented with particular attention to the first two NASA balloon to mobile vehicle propagation experiments. Some physical insight into the interpretation of propagation effects in LMSS transmissions is provided.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Microwave Journal (ISSN 0026-2897); 28; 111
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    Scattering from thin dielectric disks (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A solution was obtained for scattering from thin dielectric disks by approximating the currents induced inside the disk with the currents which would exist inside a dielectric slab of the same thickness, orientation and dielectic properties. This approximation reduces to an electrostatic approximation when the disk thickness, T, is small compared to the wavelength of the incident radiation and the approximation yields a conventional physical optics solution when the dimension, A, characteristic of the geometrical cross section of the disk (e.g., the diameter of a circular disk) is large compared to wavelength. When the ratio A/T sufficiently large the disk will always be in one or the other of these regimes, T lambda or kA1. Consequently, when A/T is large this solution provides a conventional approximation for the scattered fields which can be applied at all frequencies. As a check on this conclusion, a comparison was made between the theoretical and measured radar cross section of thin dielectric disks. Agreement was found for thin disks with both large and small values of kA.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-33; 1410-141
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    Microwave holography of large reflector antennas - Simulation algorithms (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The performance of large reflector antennas can be improved by identifying the location and amount of their surface distortions and correcting them. To determine the accuracy of the constructed surface profiles, simulation studies are used to incorporate both the effects of systematic and random distortions, particularly the effects of the displaced surface panels. In this paper, different simulation models are investigated, emphasizing a model based on the vector diffraction analysis of a curved reflector with displaced panels. The simulated far-field patterns are then used to reconstruct the location and amount of displacement of the surface panels by employing a fast Fourier transform/iterative procedure. The sensitivity of the microwave holography technique based on the number of far-field sampled points, level of distortions, polarizations, illumination tapers, etc., is also examined.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-33; 1194-120
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    Directivity optimization of a reflector antenna with cluster feeds - A closed-form solution (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The directivity of a reflector antenna deteriorates as the feed moves away from the focal point for beam scanning. This deterioration can be substantially reduced if a cluster feed instead of single feed is used to control a beam. A closed-form solution is presented for the cluster excitation to achieve the optimum directivity. For an offset 108 lambda parabolic reflector scanning 10 beamwidths, the optimum directivity achieved by a 19-element (seven-element) cluster is 12 dB (8 dB) higher than that of a single element. Comparison of the optimum-directivity design and the popular conjugate field matching design is made. When the cluster spacing d is greater than 1 lambda, it is found that the optimum directivity is higher than that of conjugate field matching (CFM) scheme by an insignificant amount, although the excitations of two designs can be quite different. For d less than 0.5 lambda, the optimum design may exhibit the supergain phenomenon, namely extremely high directivities achieved by an oscillatory cluster excitation.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-33; 1163-117
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    Fade margin calculation for channels impaired by Rician fading (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Excess path loss due to multipath severely restricts the performance of power limited mobile networks such as those using satellite-aided links. To reduce multipath related losses, the higher elevation angle of the spacecraft can be exploited by utilizing mobile antennas which reduce the strength of the multipath reflections in favor of the line-of-sight signal. The presence of a strong and stable path in a fading link will change the envelope statistics of the received waveform from Rayleigh to a more favorable Rician distribution. It is determined that the excess path loss, or fade margin, of a Rician channel when coherent detection of binary phase shift keying (BPSK) or quaternary phase shift keying (QPSK) signals is considered. The results are presented parametrically such that they can be applied to a wide range of propagation characteristics from heavy fading to nonfading situations. Furthermore, similar results are also given for the case where only limited coverage is provided.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Vehicular Technology (ISSN 0018-9545); VT-34; 41-44
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    Effects of deterministic surface distortions on reflector antenna performance (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Systematic distortions of reflector antenna surfaces can cause antenna radiation patterns to be undesirably different from those of perfectly smooth reflector surfaces. In this paper, a simulation model for systematic distortions is described which permits an efficient computation of the effects of distortions in the reflector pattern. The model uses a vector diffraction physical optics analysis for the determination of both the co-polar and cross-polar fields. An interpolation scheme is also presented for the description of reflector surfaces which are prescribed by discrete points. Representative numerical results are presented for reflectors with sinusoidally and thermally distorted surfaces. Finally, comparisons are made between the measured and calculated patterns of a slowly-varying distorted offset parabolic reflector.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Annales des Telecommunications (ISSN 0003-4347); 40; 350-360
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  • 66
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    Signal processing in SETI (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It is believed that the Galaxy might contain ten billion potential life sites. In view of the physical inaccessibility of extraterrestrial life on account of the vast distances involved, a logical first step in a search for extraterrestrial intelligence (SETI) appears to be an attempt to detect signals already being radiated. The characteristics of the signals to be expected are discussed together with the search strategy of a NASA program. It is pointed out that all presently planned searches will use existing radio-astronomy antennas. If no extraterrestrial intelligence signals are discovered, society will have to decide whether SETI justifies a dedicated facility of much greater collecting area. Attention is given to a multichannel spectrum analyzer, CW signal detection, pulse detection, the pattern detector, and details of SETI system operation.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Computer (ISSN 0018-9162); 18; 37-47
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  • 67
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    Error and erasure probabilities for Galileo uplink code (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The Galileo uplink Frame Erasure probability and Undetected Frame Error probability are derived. The performance meets desired specification under normal operations. The Galileo command system will work well even in an emergency condition, where the bit error rate into the command decoder is 1.00 X 0.001 (although Galileo's command threshold error rate is 1.00 X 0.00001).
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 165-179
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    Mark 4A project training evaluation (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A participant evaluation of a Deep Space Network (DSN) is described. The Mark IVA project is an implementation to upgrade the tracking and data acquisition systems of the dSN. Approximately six hundred DSN operations and engineering maintenance personnel were surveyed. The survey obtained a convenience sample including trained people within the population in order to learn what training had taken place and to what effect. The survey questionnaire used modifications of standard rating scales to evaluate over one hundred items in four training dimensions. The scope of the evaluation included Mark IVA vendor training, a systems familiarization training seminar, engineering training classes, a on-the-job training. Measures of central tendency were made from participant rating responses. Chi square tests of statistical significance were performed on the data. The evaluation results indicated that the effects of different Mark INA training methods could be measured according to certain ratings of technical training effectiveness, and that the Mark IVA technical training has exhibited positive effects on the abilities of DSN personnel to operate and maintain new Mark IVA equipment systems.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 134-164
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  • 69
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    The MU radar: Current status and first results (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The MU (Middle and Upper Atmosphere) radar is a 46.5 MHz pulse modulated monostatic Doppler radar with an active phased array system. The nominal beam width is 3.6 deg, and the peak radiation power is 1 MW with maximum average power of 50 kW. A brief description of the system and the initial observational results are presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Handbook for MAP, Vol. 18; 5 p
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  • 70
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    Evaluate interference in digital channels (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Any future mobile satellite service (MSS) which is to provide simultaneous mobile communications for a large number of users will have to make very efficient use of the spectrum. As the spectrum available for an MSS is limited, the system's channels should be packed as closely together as possible, with minimum-width guard bands. In addition the employment of frequency reuse schemes is an important factor. Difficulties regarding these solutions are related to the introduction of interference in the link. A balance must be achieved between the competing aims of spectrum conservation and low interference. While the interference phenomenon in narrowband FM voice channels is reasonably well understood, very little effort, however, has been devoted to the problem in digital radios. Attention is given to work, which illuminates the effects of cochannel and adjacent channel interference on digital FM (FSK) radios.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Microwaves & RF (ISSN 0745-2993); 24; 97
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  • 71
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    Direct-detection optical communication with color coded pulse position modulation signaling (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The performance characteristics of a direct-detection optical communication system which is based on a laser transmitter which produces single light pulses at selected nonoverlapping optical center frequencies are discussed. The signal format, called color coded pulse position modulation (CCPPM), uses more of the total available response bandwidth characteristics of the photodetector than does ordinary PPM signaling. The advantages of CCPPM signaling are obtained at the expense of an increased optical bandwidth of the transmitted signal and a more complicated transmitter and receiver structure. When the signal format is used in conjunction with block length Reed-Solomon codes, high data rates and reliable high-speed optical communications under conditions of optimal energy efficiency are obtained.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-33; 273-276
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  • 72
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    Long-delayed radio echoes - Mechanisms and observations (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Experiments carried out in Alaska with the object of observing long-delayed radio echoes (LDE) are described. The results are subjected to critical sonogram analysis, together with data form previous experiments carried out at Stanford and elsewhere. It is concluded that, although strong supporting evidence for sporadic LDE phenomena has accumulated over the late 50 years, and a variety of plausible mechanisms have been proposed, stringent analysis of records such as those discussed in the paper almost invariably reveal alternative possible explanations for them. Further detailed experimentation is required on mechanisms, for which the phenomenon seems best established, e.g., round-the-world echoes and other forms of guided propagation.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 1523-153
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  • 73
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    Acousto-optic techniques for real SAR imaging (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Recent advancements in the development of the Real Time Acousto-optic SAR Processor are presented. In particular, the technique for introducing the azimuth reference function into the processor via an acousto-optic Bragg cell is discussed. This approach permits the reference function to be stored in electronic memory, thus giving the processor the flexibility needed to adapt rapidly to changes in the radar/target geometry. The architecture is described and results are presented which show the applicability of the technique to both spot-light and strip-map SAR.
    Keywords: COMMUNICATIONS AND RADAR
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    Bit synchronization of differentially detected MSK and GMSK (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The filter-square bit synchronizer has been previously proposed and shown to give near optimum performance for coherent PSK systems. In this paper, the same bit synchronization scheme is analyzed for a differentially detected GMSK system. It is shown that the filter-square bit synchronizer can successfully work in a differential phase detection receiver. By making linear approximations appropriate for high loop signal-to-noise ratio operation (the usual case of interest in tracking), it is demonstrated that the mean-square bit sync jitter of differentially detected GMSK system reveals striking similarities both qualitatively and quantitatively in comparison with that of a coherent PSK system.
    Keywords: COMMUNICATIONS AND RADAR
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    Combined trellis coding with asymmetric modulations (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The use of asymmetric signal constellations combined with optimized trellis coding to improve the performance of coded systems without increasing the average or peak power, or changing the bandwidth constraints of a system is discussed. The trellis code, asymmetric signal set, and Viterbi decoder of the system model are examined. The procedures for assigning signals to state transitions of the trellis code are described; the performance of the trellis coding system is evaluated. Examples of AM, QAM, and MPSK modulations with short memory trellis codes are presented.
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    Criteria for site selection and frequency allocation (keynote paper), part 5 (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Technical aspects of mesosphere-stratosphere-troposphere (MST) Radar on site and frequency selection were discussed. Recommendations on site selections are presented. Tests of interference will be conducted before selecting a site. A small directional antenna may be suitable to simulate sidelobe sensitivity of radars however, sophisticated data-processing methods make system sensitivity extremely good. The use of the complete data system to look for interference is recommended. There is the difficulty of allocation of frequencies -- almost continuous use by these radars will be made when the band 40 to 60 MHz is allocated to other services.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program: Handbook for MAP. Vol. 14; p 234-244
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    Antenna Technology for QUASAT application (1985)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: A hybrid growth version of the advanced Sunflower, or precision deployable, antenna was adopted as the configuration proposed for the QUASAT very long baseline interferometry mission. The antenna consists of rigid panels of graphite-epoxy facesheets covering aluminum honeycomb sandwich. The six main folding panels are hinged to a cantilevered support ring attached to the periphery of the center section. Six pairs of intermediate panels are located between these panels and are hinged to each other and to the main panels. The flight configuration, antenna weight, a mass properties, frequency, and contour tolerance are discussed. The advantages of the solid antenna surface cover an all-mesh contour are examined.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Langley Research Center Large Space Antenna Systems Technol., 1984; p 251-270
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    QUASAT: An orbiting very long baseline interferometer program using large space antenna systems (1985)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: QUASAT, which stands for QUASAR SATELLITE, is the name given to a new mission being studied by NASA. The QUASAT mission concept involves a free flying Earth orbiting large radio telescope, which will observe astronomical radio sources simultaneously with ground radio telescopes. The primary goal of QUASAT is to provide a system capable of collecting radio frequency data which will lead to a better understanding of extremely high energy events taking place in a variety of celestial objects including quasars, galactic nuclei, interstellar masers, radio stars and pulsars. QUASAT's unique scientific contribution will be the increased resolution in the emission brightness profile maps of the celestial objects.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Langley Research Center Large Space Antenna Systems Technol., 1984; p 117-125
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    Advanced 2-frequency ocean sensing radar using high resolution antenna beams (1985)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The opportunity to use a large space antenna system for remote sensing applications permits the creation of an advanced ocean sensing radar that combines the abilities of previously developed techniques. The 15 meter antenna will permit much higher angular and spatial resolution at the surface that will lead to techniques of observing ocean wave heights and the directional spectrum that had not previously been feasible from space. At the same time, sensors to measure ocean surface winds can be in operation and the data from both can be combined to increase the accuracy of each individual sensor. The existing capabilities and sensor techniques with typical data characteristics for the individual measurement of sea surface quantities are outlined.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Large Space Antenna Systems Technol., 1984; p 109-115
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  • 80
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    Alternatives for satellite sound broadcast systems at HF and VHF (1985)
    In:  CASI
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    Publication Date: 2017-10-02
    Description: The National Aeronautics and Space Administration and the United States Information Agency (USIA) are currently engaged in a joint program to assess the technical and economic feasibility of direct sound broadcast satellite systems to meet USIA mission needs. The cooperative effort calls for a series of interrelated studies to provide the respective Agency managements with information on the potential role of direct broadcast satellites. Initial studies focused on HF propagation phenomena and broadcast coverage requirements. These studies served as the basis for parallel systems studies currently in progress. The systems studies are to provide a data base on various satellite configurations and systems concepts capable of supporting potential broadcast requirements ranging from a small fraction to a substantial addition to USIA requirements. Antenna concepts for LEO and GEO orbits are briefly described.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Langley Research Center Large Space Antenna Systems Technol., 1984; p 27-37
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  • 81
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    Low-frequency microwave radiometer for N-ROSS (1985)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The all weather, global determination of sea surface temperature (SST) has been identified as a requirement needed to support naval operations. The target SST accuracy is + or - 1.0 K with a surface resolution of 10 km. Investigations of the phenomenology and technology of remote passive microwave sensing of the ocean environment over the past decade have demonstrated that this objective is presently attainable. Preliminary specification and trade off studies were conducted to define the frequency, polarization, scan geometry, antenna size, and other esstential parameters of the low frequency microwave radiometer (LFMR). It will be a dual polarized, dual frequency system at 5.2 and 10.4 GHz using a 4.9 meter deployable mesh surface antenna. It is to be flown on the Navy-Remote Ocean Sensing System (N-ROSS) satellite scheduled to be launched in late 1988.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Langley Research Center Large Space Antenna Systems Technol., 1984; p 87-95
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    Characterization of MMIC devices for active array antennas (1985)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: Certain aspects of monlithic microwave integrated circuit (MMIC) interconnectivity were investigated. Considerations that lead to preserving the inherently reproducible characteristics of the MMIC are proposed. It is shown that at radio frequencies (RF) greater than 20 GHz, the transition from the MMIC device to other transmission media must be an accurate RF match. It is proposed that the RF match is sufficiently critical to include the transition as part of the delivered MMIC package. The model to analyze several transitions is presented. This model consists of a succession of abrupt discontinuities in printed circuit transmission lines. The analysis of these discontinuities is achieved by the Spectral Galerkin technique, to establish the modes and mode that special effects should be coordinated by the active array antenna industry toward standardization of MMIC packaging and characterization.
    Keywords: COMMUNICATIONS AND RADAR
    Type: RADC Proc. of the 1984 Antenna Appl. Symp.; p 57-82
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  • 83
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    A uniform GTD analysis of the EM diffraction by a thin dielectric/ferrite half-plane and related configurations (1985)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: A uniform geometrical theory of diffraction (UTD) solution is developed for the problem of the diffraction by a thin dielectric/ferrite half plane when it is excited by a plane, cylindrical, or surface wave field. Both transverse electric and transverse magnetic cases are considered. The solution of this problem is synthesized from the solutions to the related problems of EM diffraction by configurations involving perfectly conducting electric and magnetic walls covered by a dielectric/ferrite half-plane of one half the thickness of the original half-plane.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-181251 , NAS 1.26:181251 , REPT-716199-5
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    Airborne antenna radiation pattern code user's manual (1985)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The use of a newly developed computer code to analyze the radiation patterns of antennas mounted on a ellipsoid and in the presence of a set of finite flat plates is described. It is shown how the code allows the user to simulate a wide variety of complex electromagnetic radiation problems using the ellipsoid/plates model. The code has the capacity of calculating radiation patterns around an arbitrary conical cut specified by the user. The organization of the code, definition of input and output data, and numerous practical examples are also presented. The analysis is based on the Uniform Geometrical Theory of Diffraction (UTD), and most of the computed patterns are compared with experimental results to show the accuracy of this solution.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-181249 , NAS 1.26:181249 , REPT-716199-4
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    Intelligence/Electronic Warfare (IEW) direction-finding and fix estimation analysis report. Volume 2: Trailblazer (1985)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: An analysis of the direction finding (DF) and fix estimation algorithms in TRAILBLAZER is presented. The TRAILBLAZER software analyzed is old and not currently used in the field. However, the algorithms analyzed are used in other current IEW systems. The underlying algorithm assumptions (including unmodeled errors) are examined along with their appropriateness for TRAILBLAZER. Coding and documentation problems are then discussed. A detailed error budget is presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-181138 , NAS 1.26:181138 , JPL-D-180-VOL-2 , AD-A180468
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    Wind dynamic range video camera (1985)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: A television camera apparatus is disclosed in which bright objects are attenuated to fit within the dynamic range of the system, while dim objects are not. The apparatus receives linearly polarized light from an object scene, the light being passed by a beam splitter and focused on the output plane of a liquid crystal light valve. The light valve is oriented such that, with no excitation from the cathode ray tube, all light is rotated 90 deg and focused on the input plane of the video sensor. The light is then converted to an electrical signal, which is amplified and used to excite the CRT. The resulting image is collected and focused by a lens onto the light valve which rotates the polarization vector of the light to an extent proportional to the light intensity from the CRT. The overall effect is to selectively attenuate the image pattern focused on the sensor.
    Keywords: COMMUNICATIONS AND RADAR
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    Radiofrequency testing of satellite segment of simulated 30/20 GHz satellite communications system (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A laboratory communications system has been developed that can serve as a test bed for the evaluation of advanced microwave (30/20 GHz) components produced under NASA technology programs. The system will ultimately permit the transmission of a stream of high-rate (220 Mbps) digital data from the originating user, through a ground terminal, through a hardware-simulated satellite, to a receiving ground station, to the receiving user. This report contains the results of radiofrequency testing of the satellite portion of that system. Data presented include output spurious responses, attainable signal-to-noise ratios, a baseline power budget, usable frequency bands, phase and amplitude response data for each of the frequency bands, and the effects of power level variation.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-87163 , E-2797 , NAS 1.15:87163
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    Gain-adaptive vector quantization for medium-rate speech coding (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A class of adaptive vector quantizers (VQs) that can dynamically adjust the 'gain' of codevectors according to the input signal level is introduced. The encoder uses a gain estimator to determine a suitable normalization of each input vector prior to VQ coding. The normalized vectors have reduced dynamic range and can then be more efficiently coded. At the receiver, the VQ decoder output is multiplied by the estimated gain. Both forward and backward adaptation are considered and several different gain estimators are compared and evaluated. An approach to optimizing the design of gain estimators is introduced. Some of the more obvious techniques for achieving gain adaptation are substantially less effective than the use of optimized gain estimators. A novel design technique that is needed to generate the appropriate gain-normalized codebook for the vector quantizer is introduced. Experimental results show that a significant gain in segmental SNR can be obtained over nonadaptive VQ with a negligible increase in complexity.
    Keywords: COMMUNICATIONS AND RADAR
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    I/Q reversal phenomena in 4-phase modified Costas Loops (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A method for predicting the occurrence of I/Q reversals in unbalanced QPSK 4-phase modified Costas Loops is discussed. Potential causes for the reversal of in-phase and quadrature outputs of the unbalanced QPSK demodulator during acquisition and tracking are studied. The design of the unbalance QPSK demodulator and loop characteristics are described. The effect of an anomalous condition during a transient interval or demod/remod operation on data source output is examined. Filtering and hard-limiting effects, and the demodulator loop S-curve stability during tracking are evaluated.
    Keywords: COMMUNICATIONS AND RADAR
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    A multiple scattering theory for EM wave propagation in a dense random medium (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: For a dense medium of randomly distributed scatterers an integral formulation for the total coherent field has been developed. This formulation accounts for the multiple scattering of electromagnetic waves including both the twoand three-particle terms. It is shown that under the Markovian assumption the total coherent field and the effective field have the same effective wave number. As an illustration of this theory, the effective wave number and the extinction coefficient are derived in terms of the polarizability tensor and the pair distribution function for randomly distributed small spherical scatterers. It is found that the contribution of the three-particle term increases with the particle size, the volume fraction, the frequency and the permittivity of the particle. This increase is more significant with frequency and particle size than with other parameters.
    Keywords: COMMUNICATIONS AND RADAR
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  • 91
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    Noncoherent sampling technique for communications parameter estimations (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: This paper presents a method of noncoherent demodulation of the PSK signal for signal distortion analysis at the RF interface. The received RF signal is downconverted and noncoherently sampled for further off-line processing. Any mismatch in phase and frequency is then compensated for by the software using the estimation techniques to extract the baseband waveform, which is needed in measuring various signal parameters. In this way, various kinds of modulated signals can be treated uniformly, independent of modulation format, and additional distortions introduced by the receiver or the hardware measurement instruments can thus be eliminated. Quantization errors incurred by digital sampling and ensuing software manipulations are analyzed and related numerical results are presented also.
    Keywords: COMMUNICATIONS AND RADAR
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  • 92
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    Asymptotic high frequency analysis of the electromagnetic backscattering from an inlet model consisting of piecewise linearly tapered sections (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Electromagnetic backscattering from an open ended three dimensional inlet model is analyzed and computed patterns are compared with results of experimental measurements. The model is comprised of two sections. The first section consists of a linearly tapered waveguide with a rectangular opening at one end and the other end is connected to the second section which is a uniform rectangular waveguide with a planar perfectly conducting termination. The model is electrically large so that many propagating modes are excited. The method of analysis contains conventional aperture integration and modal techniques combined with high frequency techniques, which employ concepts such as modal rays, geometrical theory of diffraction and equivalent currents. For the cases considered, it is shown that only a few of the many propagating modes contribute appreciably to the backscattered field. These modes are selected according to their modal ray angle directions.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-176844 , NAS 1.26:176844 , OSU-TR-716148-6
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  • 93
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    Consideration of radar target glint from ST during OMV rendezvous (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The nature of radar target glint and the factors upon which it depends when using the Hubble Space Telescope as a radar target is discussed. An analysis of the glint problem using a 35 MHz or 94 MHz radar on the orbital maneuvering vehicle is explored. A strategy for overcoming glint is suggested.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-86533 , NAS 1.15:86533
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  • 94
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    Analysis of airborne antenna systems using geometrical theory of diffraction and moment method computer codes (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Computer codes have been developed to analyze antennas on aircraft and in the presence of scatterers. The purpose of this study is to use these codes to develop accurate computer models of various aircraft and antenna systems. The antenna systems analyzed are a P-3B L-Band antenna, an A-7E UHF relay pod antenna, and traffic advisory antenna system installed on a Bell Long Ranger helicopter. Computer results are compared to measured ones with good agreement. These codes can be used in the design stage of an antenna system to determine the optimum antenna location and save valuable time and costly flight hours.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-181248 , NAS 1.26:181248 , REPT-716199-6
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  • 95
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    On the convergence of an iterative formulation of the electromagnetic scattering from an infinite grating of thin wires (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Contraction theory is applied to an iterative formulation of electromagnetic scattering from periodic structures and a computational method for insuring convergence is developed. A short history of spectral (or k-space) formulation is presented with an emphasis on application to periodic surfaces. The mathematical background for formulating an iterative equation is covered using straightforward single variable examples including an extension to vector spaces. To insure a convergent solution of the iterative equation, a process called the contraction corrector method is developed. Convergence properties of previously presented iterative solutions to one-dimensional problems are examined utilizing contraction theory and the general conditions for achieving a convergent solution are explored. The contraction corrector method is then applied to several scattering problems including an infinite grating of thin wires with the solution data compared to previous works.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-177235 , NAS 1.26:177235
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  • 96
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    On the electromagnetic scattering from infinite rectangular conducting grids (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The study and development of two numerical techniques for the analysis of electromagnetic scattering from a rectangular wire mesh are described. Both techniques follow from one basic formulation and they are both solved in the spectral domain. These techniques were developed as a result of an investigation towards more efficient numerical computation for mesh scattering. These techniques are efficient for the following reasons: (a1) make use of the Fast Fourier Transform; (b2) they avoid any convolution problems by converting integrodifferential equations into algebraic equations; and (c3) they do not require inversions of any matrices. The first method, the SIT or Spectral Iteration Technique, is applied for regions where the spacing between wires is not less than two wavelengths. The second method, the SDCG or Spectral Domain Conjugate Gradient approach, can be used for any spacing between adjacent wires. A study of electromagnetic wave properties, such as reflection coefficient, induced currents and aperture fields, as functions of frequency, angle of incidence, polarization and thickness of wires is presented. Examples and comparisons or results with other methods are also included to support the validity of the new algorithms.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-177236 , NAS 1.26:177236
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    Angular power spectrums and their relationship to autocorrelation functions of aperture antennas (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Normalized angular power spectrum representations have been derived for linear and circular aperture antennas in terms of their autocorrelation functions. Examples of their use are given.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-87630 , NAS 1.15:87630
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  • 98
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    Secondary pattern computation of an offset reflector antenna (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Reflector antennas are widely used in communications satellite systems because they provide high gain at low cost. In analyzing reflector antennas the computation of the secondary pattern is the main concern. A computer program for calculating the secondary pattern of an offset reflector has been developed and implemented at the NASA Lewis Research Center. The theoretical foundation for this program is based on the use of geometrical optics to describe the fields from the feed to the reflector surface and to the aperture plane. The resulting aperture field distribution is then transformed to the far-field zone by the fast Fourier transform algorithm. Comparing this technique with other well-known techniques (the geometrical theory of diffraction, physical optics (Jacobi-Bessel), etc.) shows good agreement for large (diameter of 100 lambda or greater) reflector antennas.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-87160 , E-2791 , NAS 1.15:87160
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  • 99
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    Analog FM/FM versus digital color TV transmission aboard space station (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Langley Research Center is developing an integrated fault tolerant network to support data, voice, and video communications aboard Space Station. The question of transmitting the video data via dedicated analog channels or converting it to the digital domain for consistancy with the test of the data is addressed. The recommendations in this paper are based on a comparison in the signal-to-noise ratio (SNR), the type of video processing required aboard Space Station, the applicability to Space Station, and how they integrate into the network.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-87578 , NAS 1.15:87578
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  • 100
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    Secondary pattern computation of an arbitrarily shaped main reflector (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The secondary pattern of a perfectly conducting offset main reflector being illuminated by a point feed at an arbitrary location is studied. The method of analysis is based upon the application of the Fast Fourier Transform (FFT) to the aperture fields obtained using geometrical optics (GO) and geometrical theory of diffraction (GTD). Key features of the present work are (1) the reflector surface is completely arbitrary, (2) the incident field from the feed is most general with arbitrary polarization and location, and (3) the edge diffraction is calculated by either UAT or by UTD. Comparison of this technique for an offset parabolic reflector with the Jacobi-Bessel and Fourier-Bessel techniques shows good agreement. Near field, far field, and scan data of a large refelctor are presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-87162 , E-2796 , NAS 1.15:87162
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