ALBERT

Description: In this paper, an output-controllable digital predistortion (DPD) technique is proposed to partially inverse the nonlinear behavior of RF power amplifiers (PAs). Compared to the existing DPD, the proposed method changes the goal that the PA output must be exactly the same as the original input to a new one that the PA output can be arbitrarily controlled according to user's demand. The proposed approach largely expands the capability of DPD and thus provides more flexibility for system designers to effectively use DPD to manipulate the PA output in order to handle more application scenarios and objectively conduct further system optimization. Various application cases have been tested. The experimental results demonstrate that the proposed approach has great potential in future wireless communication system design.

Description: Any amplifier operated with a varying supply voltage is actually a three-port circuit, having two inputs and one output. When an amplifier is characterized as a three-port for dynamic supply voltage operation, three separate operating modes appear: linear L-mode and the two nonlinear modes C-mode and P-mode. Each of these modes, along with their relationships and differences, are identified, characterized, and discussed. Relations of these modes to the dynamic power supply transmitter techniques of envelope tracking and/or direct polar are presented. Measurements are reported that provide experimental verification for these amplifier operating modes.

Description: In this paper, a Doherty power amplifier for K-band point-to-point microwave radio, developed in TriQuint GaAs ${hbox{0.15-}}{mu{hbox {m}}}$ PWR pHEMT monolithic technology, is presented. Highly efficient driver stages on both the main and auxiliary branches have been designed and optimized to boost gain with minimal impact on power-added efficiency. The selected architecture enables a modular combination to reach higher power levels. Matching network structures have been designed, according to simple equivalent circuit approaches, to obtain the desired 10% fractional bandwidth. The fabricated power amplifier (PA) exhibits, at 24 GHz in continuous-wave conditions, an output power of 30.9 dBm, with a power-added efficiency of 38% at saturation and 20% at 6 dB of output power back-off, together with a gain of 12.5 dB. System-level characterization at 24 GHz, in very demanding conditions, with a 28-MHz channel 7.5-dB peak-to-average ratio modulated signal, showed full compliance with the standard emission mask, adopting a simple predistorter, with average output power of 23.5 dBm, and average efficiency above 14%. The measured performance favorably compare with other academic and commercial K-band PAs for similar applications.

Description: A novel single-source surface–volume–surface integral equation is proposed for accurate broadband resistance and inductance extraction in 3-D interconnects. The new equation originates in the volume integral equation (VIE) traditionally used for magneto-quasi-static modeling of current flow in 3-D wires. The latter is reduced to a surface integral equation by representing the electric field inside each conductor segment as a superposition of cylindrical waves emanating from the conductor's boundary. As no approximation is utilized and all underlying boundary conditions and pertinent equations are satisfied in the reduction, the new integral equation is rigorously equivalent to the solution of the traditional volume electric field integral equation. The rigorous nature of the proposed single-source surface integral equation is corroborated numerically. In this paper, a detailed description of the method of moments discretization for the proposed surface integral equation is also presented. Numerical solution of the proposed surface integral equation for a 12-conductor bond-wire package is used to demonstrate the accuracy of the method and its computational benefits compared to the traditional solution based on the VIE.

Description: This paper presents a method for pruning power amplifier (PA) behavioral models and digital predistorters based on compressed sampling theory. Using this method, the number of coefficients required by behavioral models and predistorters can be significantly reduced while achieving comparable performance in terms of both modeling accuracy and suppressing distortions. Hardware measurements obtained for a Doherty PA driven by a five-carrier 100-MHz wide long-term evolution-advanced signal demonstrate the capability of the proposed method to linearize a highly nonlinear PA prototype using a minimal number of coefficients, revealing the attractive properties of the proposed method and its desirable performance. Using the proposed technique, predistorters achieving similar linearization performance while requiring significantly less coefficients than the traditional models were demonstrated.

Description: This paper presents a new baseband equivalent (BBE) Volterra-series model suitable for the behavioral modeling and linearization of wideband RF power amplifiers (PAs). Starting with passband Volterra series, and following a number of signal transformations, a discrete expression relating the envelopes of the output and input signals to the carrier frequency was derived. The new BBE Volterra series reduces the number of kernels, and hence, avoids resorting to the pruning approaches commonly applied in the literature to the classical low-pass equivalent (LPE) Volterra formulation. The proposed baseband Volterra series has similar modeling and linearization performance to the full classical LPE Volterra series. It also outperforms the pruned LPE Volterra models, which use a dynamic deviation reduction approach, in terms of both linearization performance and complexity. The proposed BBE Volterra series was successfully used to linearize different PAs (200-W LDMOS Doherty and 45-W broadband GaN PA) driven with wideband and intra-band carrier aggregated signals (mixed LTE and WCDMA signals).

Description: A compact self-packaged dual-band filter structure using multilayer liquid crystal polymer technology is presented in this paper. The frequency and bandwidth of each passband can be more conveniently controlled by means of vertically embedded elements, i.e., metal patches, placed above the coupled folded multi-stepped impedance resonators. The packaged solution is connected to the outer environment through a coplanar waveguide that allows flip-chip interconnection to a host board. The proposed design is validated with the fabrication of two prototypes. The measured results show good agreement with the simulations.

Description: In the paper, the nonlinear model of a microwave transistor is extracted from large-signal measurements acquired under “dynamic-bias” operation. Specifically, the transistor is driven by low-frequency large signals while a high-frequency tickle is applied on top of them. The low-frequency large signals, along with the dc bias voltages, set the large-signal operating point which represents a dynamic-bias condition for the device under test. Thanks to this technique, one can get at once and separately the nonlinear currents and charges of the transistor as a result of a very few nonlinear measurements. Additionally, the proposed technique allows one to accurately reconstruct the time-domain waveforms at the device-under-test terminals while the frequency of the tickle can be set as high as the bandwidth of today's vector calibrated nonlinear measurement systems (i.e., 67 GHz). The approach, which is general and independent of device technology, is applied on a 0.15- $mu$ m GaAs pHEMT specifically designed for resistive cold-FET mixer applications.

Description: In this paper, an explicit and unconditionally stable finite-difference time-domain (FDTD) method is developed for electromagnetic analysis. Its time step is not restricted by the space step, and its accuracy is ensured for the time step chosen based on accuracy. The strength of the conventional explicit FDTD is thus preserved in avoiding a system matrix solution, while the shortcoming of the conventional FDTD is eliminated in the time step's dependence on space step. Numerical experiments in both 2-D and 3-D simulations have demonstrated the performance of the proposed method in stability and efficiency without sacrificing accuracy.

Description: A 0.7–1.0-GHz reconfigurable bandpass-to-bandstop filter with selectable 2- and 4-pole responses is presented. The proposed filter can act as a 2- or 4-pole bandpass or bandstop filter by changing the coupling paths using zero-value coupling coefficients. The 4-pole bandpass filter mode also includes bandwidth control. The filter is built on a Duroid substrate with $varepsilon_{ r}=10.2$ and $h=25$ mil. The center frequency tuning, as well as the bandpass-to-bandstop transformation and the selection of the number of poles are achieved using silicon varactor diodes and RF microelectromechanical systems switches. In the 2- and 4-pole bandpass modes, an insertion loss of 4.9–2.9 and 6.1–4.8 dB is measured at 0.71–0.99 and 0.72–1.01 GHz, respectively. The 4-pole bandpass mode also shows a bandwidth tuning of 28–85 MHz at 0.9 GHz. In the 2- and 4-pole bandstop modes, rejection levels of 24–28 and 32–41 dB are measured at 0.64–0.96 and 0.71–0.96 GHz, respectively. The application areas are in reconfigurable filters for wideband radios under high interference environments.

Description: An experimental approach to investigate the forward scattering sum rule for periodic structures is presented. This approach allows an upper bound on the total cross section integrated over a bandwidth from a simple static problem to be found. Based on energy conservation, the optical theorem is used to construct a relation between the total cross section and the forward scattering of periodic structures as well as single scatterers inside a parallel-plate waveguide. Dynamic measurements are performed using a parallel-plate waveguide and a parallel-plate capacitor is utilized to find the static polarizability. Convex optimization is introduced to identify the total cross section in the dynamic measurements and estimate an optimal lower bound on the polarizability for objects. The results show that the interactions between the electromagnetic field and an object over all wavelengths are given by the static polarizability of the object.

Description: In this paper, we present an efficient numerical algorithm to solve the vector wave equation in general cylindrically layered media. The method is based on the fact that appropriate choices of basis and weighting functions make it possible to separate the vector wave equation numerically. To this end, we present a set of curl-conforming vector basis functions in a 2-D doubly connected domain and another set of different vector weighting functions. The former is responsible for the avoidance of spurious solutions while the later provides a numerical separation. The proposed method is applied to calculate the propagation constants of the lower order guided and leaky modes of several cylindrically layered dielectric waveguides and the accuracy and efficiency of the method are investigated.

Description: Compact multi-port power combiners and dividers with filter characteristics are introduced. These components advantageously combine the functions of power distribution and filtering in a single component, thus reducing the number of components in a system and improving overall system performance. The design principle, which is entirely based on filter theory, is first presented for a symmetric filtering four-port combiner/divider and is then extended to an eight-port network. Measurements on a symmetric all-metal waveguide four-port prototype show excellent agreement with simulations and validate the general design approach. The experimental response of an asymmetric substrate integrated waveguide eight-port network agrees reasonably well with simulations and demonstrates that the basic four-port element can be extended to very compact multi-port combiner/dividers to cope with a variety of systems requirements.

Description: This paper presents a novel coupled line 180 $^{circ}$ hybrid with non-interspersed input/output ports. With the combination of a weak coupling parallel coupled line and strong coupling trans-directional coupler, a non-interspersed input/output ports coupled line 180 $^{circ}$ hybrid is obtained by using printed circuit board fabrication process, and reduced substrate area is achieved. The proposed hybrid owns the features of reducing the complexity of dc biasing for the next-stage active circuits. Moreover, it requires no bond wires, via-holes, or multilayer structures. The formula of the proposed hybrid is derived, and the characteristics of the hybrid are analyzed. Two prototypes are designed to verify the concept. One is arranged with the two couplers perpendicular to each other, and the other is constructed with the two couplers arranged in a line. The measured results are in good agreement with the simulated ones

Description: In this paper, an $E$ -plane waveguide power divider and a waveguide-to-microstrip transition are used to form a waveguide magic-T with four arms in the same $E$ -plane. The input port of the original $E$ -plane waveguide power divider acts as the difference port of the magic-T, and a waveguide-to-microstrip transition is utilized to realize the sum port. The four arms are in the same plane, and traditional matching elements, such as cones, wedges, pins, and irises are not needed. The proposed magic-T features easy connection, fabrication, and assembly. The principle and design procedure are described in detail. A $Ka$ -band $E$ -plane waveguide magic-T is designed, fabricated, and measured. A fractional bandwidth of 21% is achieved. The measured and simulated results show good amplitude, phase, and isolation characteristics validating the proposed magic-T.

Description: This paper presents a 90-nm fully integrated CMOS linear power amplifier (PA) using a coupled L-shape concentric vortical transformer (CL-CVT) for the fourth-generation long-term evolution (LTE) communication standard. Using the proposed output combining CL-CVT architecture, the outer diameter required by the power combiner is reduced by 66% compared to the distributed active transformer with similar performance. Moreover, the PA is able to efficiently combine four push–pull output stages and achieve nearly constant power over several LTE bands with a total chip area less than 1 ${hbox {mm}}^{2}$ . With a 1.2-V supply voltage, the PA delivers 27.3-dBm maximum output power with a peak drain efficiency of 47% at 2.4 GHz. Using a 20-MHz LTE 16-QAM test signal, the PA achieves 24.6% power-added efficiency at an output power level of 22 dBm and passes the spectral requirements defined by the LTE standard without using any pre-distortion or calibration techniques.

Description: This paper addresses, for the first time, the digital representation of spectrally periodic signal-interference microwave passive filters. Starting from the theoretical rational transfer function of a synthesized transmission-line signal-interference analog filter, the real-valued coefficients of its digital-domain filter counterpart are derived. This discrete-time formulation for this type of microwave filters allows to clarify some confusing concepts into them, such as filter order. Moreover, some particular phenomena observed in associated experimental proof-of-concept planar prototypes, such as the appearance of out-of-band/spurious resonance peaks, are also explained by this study as zero-pole quasi-cancellations. In addition, it is demonstrated here that the use of the adjective “transversal” for this class of microwave passive filters could be no rigorous as it is understood in a digital sense since its discrete-time modeling commonly obeys an infinite-impulse-response structure. For validation, the expounded theoretical framework is applied to three examples of signal-interference passive filters exhibiting quasi-elliptic-type single-passband, six-passband, and low-pass responses.

Description: In this study, we propose an auxiliary power regulator (APR) for the current-shared cascade (CSC) structure of the driver stages of RF CMOS power. Although the CSC structure provides a method to reduce the power consumption at the driver stages of a differential power amplifier (PA), it is difficult to obtain optimum levels of effective supply voltage for the first and second driver stages. Additionally, the transistor sizes of the first and second driver stages of the CSC structure must be identical to ensure the proper operation of the PA. Thus, in this work, we propose an APR structure that ensures the proper operation of a PA with different transistor sizes in its first and second driver stages. To prove the feasibility of the proposed technique, we designed the PA with a CSC structure using an APR. From the measured results, we successfully verify the feasibility of the proposed structure. Additionally, we provide experimental results for a typical CMOS PA to determine the optimum supply voltage for the second driver stage.

Description: The pin-to-pin electrostatic discharge (ESD) issue for a differential low-noise amplifier (LNA) was studied in this work. A new design of ESD protection diodes with an embedded silicon-controlled rectifier (SCR) was proposed to protect the gigahertz differential LNA. The proposed ESD protection design was modified from the conventional ESD protection design without adding any extra device. The SCR path was established directly from one differential input pad to the other differential input pad so the pin-to-pin ESD robustness can be improved. This design had been verified in a 65-nm CMOS process. Besides, this design had been further applied to a 24-GHz LNA in the same 65-nm CMOS process. Experimental results had shown that the proposed ESD protection design for the differential LNA can achieve excellent ESD robustness and good RF performances.

Description: This paper provides a formulation of the dual-tapped microstrip resonator. The formulation derives the $Q$ -factor of the resonator, and the maximum value of the $Q$ -factor while still satisfying oscillation conditions. It is shown that the optimized $Q$ -factor can be determined without changing the resonant frequency bandwidth. The phase-noise performance of a voltage-controlled oscillator (VCO) using a dual-tapped microstrip resonator can therefore be designed independent of the design of the oscillation bandwidth. This feature results in simple design of low phase-noise VCOs while maintaining the desired oscillation bandwidth. Experimental results of an X-band VCO employing the dual-tapped microstrip resonator verify the theoretical findings. The fabricated X-band VCO achieves an oscillation bandwidth of 11.86–12.09 GHz and phase noise lower than ${-}{hbox{114.4}}$ dBc/Hz at 100-kHz offset from the carrier. This VCO is one of the most low phase-noise planar X-band VCOs published to date.

Description: Co-design of 60-GHz wideband front-end integrated circuit (IC) with on-chip transmit/receive (T/R) switch in 65-nm CMOS is presented. Passive macro-modeling (pmm) is utilized to convert $S$ -parameter files from passive component electromagnetic simulations to state-space models in circuit netlist format that could be used in a commercial SPICE simulator for various analyses without convergence issues. The co-design of the on-chip switch and the low-noise amplifier (LNA)/power amplifier could achieve wideband matching and reduce the effects of insertion loss of the on-chip T/R switch. Combining with the gain-boosting technique in the LNA design and lumped-component-based design methodology, the implemented 60-GHz front-end IC with an on-chip T/R switch achieves 3-dB gain bandwidth (BW) of 12 GHz with a maximum gain of 17.8 dB and minimum noise figure of 5.6 dB in the receiver mode and 3-dB gain BW of 10 GHz with saturated output power of 5.6 dBm in the transmitter mode, and only consumes 1.0 mm $times$ 1.2 mm die area (including pads).

Description: This paper describes the analysis and design of saturated silicon–germanium (SiGe) heterojunction bipolar transistor (HBT) switches for millimeter-wave applications. A switch optimization procedure is developed based on detailed theoretical analysis and is then used to design multiple switch variants. The switches utilize IBM's 90-nm 9HP technology, which features SiGe HBTs with peak ${ f}_{ T}/{ f}_{max}$ of 300/350 GHz. Using a reverse-saturated configuration, a single-pole double-throw switch with a measured insertion loss of 1.05 dB and isolation of 22 dB is achieved at 94 GHz after de-embedding pad losses. The switch draws 5.2 mA from a 1.1-V supply, limiting power consumption to less than 6 mW. The switching speed is analyzed and the simulated turn-on and turn-off times are found to be less than 200 ps. A technique is also introduced to significantly increase the power-handling capabilities of saturated SiGe switches up to an input-referred 1-dB compression point of 22 dBm. Finally, the impact of RF stress on this novel configuration is investigated and initial measurements over a 48-h period show little performance degradation. These results demonstrate that SiGe-based switches may provide significant benefits to millimeter-wave systems.

Description: This paper presents a novel microstrip transmission line method for broadband relative permittivity measurement of planar dielectric substrate materials. The method requires three sets of $S$ -parameter measurements of the microstrip line together with an obstacle in three equidistant positions over the line. The measurement and simulation results for the broadband relative permittivity of high-frequency substrates, TLX-8, RF60A, CER10, and the widely used FR4 are presented. The errors are calculated based on the manufacturers' data sheet value. Both the simulation and measurement results are found to be within 16% of the data sheet values for CER10 and 10% for all other substrates. The proposed method can minimize errors due to the nonreproducibility of connectors and impedance mismatch problems, prevalent in transmission line methods. However, the method is highly sensitive to the positioning of the obstacle, which can be overcome through the use of high accuracy obstacle positioning methods.

Description: This paper introduces a new class of RF-to-dc rectifiers called the in-phase gate-boosting rectifier (IGR). An IGR utilizes an in-phase passive voltage multiplier (IPVM) to boost in-phase $V_{rm GS}$ swing from the driving $V_{rm DS}$ swing. This design simultaneously reduces the effective threshold voltage, forward resistance, and the reverse leakage current of the rectifying transistor. As a consequence, the sensitivity and the efficiency of a high-frequency rectifier can be improved. Furthermore, a $C_{G}$ -loaded IPVM presents low input conductance and is shunted with the drains/sources of the rectifying transistors. This makes the realization of the input matching network between the IGR core and the antenna easier, and achieves a higher voltage swing at the input terminals of the IGR core. The criteria, properties, and relating proofs of the IPVM are also discussed. A differential seven-stage millimeter-wave IGR is implemented in a 65-nm RF CMOS process. In this design, an interleaving internal threshold cancellation bias scheme is also introduced to further suppress the power consumption due to biasing circuitry without increasing the layout area. The implemented integrated circuit achieves a state-of-the-art $-$ 7-dBm sensitivity with 20% peak efficiency at 53 GHz and a bandwidth of 10 GHz from 46 to 56 GHz.

Description: We present a novel non-contact metrology approach for on-wafer characterization of sub-millimeter-wave devices, components, and integrated circuits. Unlike existing contact probes that rely on small metallic tips that make physical contact with the device on the chip, the new non-contact probes are based on electromagnetic coupling of vector network analyzer (VNA) test ports into the coplanar waveguide environment of integrated devices and circuits. Efficient signal coupling is achieved via a quasi-optical link between the VNA ports and planar antennas that are monolithically integrated with the test device. Experimental validation of the non-contact device metrology system is presented for the first time to demonstrate the accuracy and repeatability of proposed approach for the 325–500-GHz (WR2.2) and 500–750-GHz (WR1.5) bands.

Description: Most conventional wideband digital predistortion (DPD) techniques require the use of a very high-speed analog-to- digital converter (ADC) in the feedback path. This paper proposes a novel technique, termed under-sampling restoration digital predistortion (USR-DPD), to linearize wideband power amplifiers (PAs) with ADCs that operate at sampling rates much lower than required by Nyquist limits for the predistorted band (under-sampling ADCs). The USR processing is implemented in an iterative way to restore full-band PA output information from the under-sampled output signal, allowing memory DPD models to be successfully extracted. The USR-DPD can operate in two modes: without and with a band-limiting filter in the feedback path. In comparison with conventional DPD techniques, the requirement for ADC sampling frequency can be significantly reduced using the USR-DPD approach. Experimental tests were realized for two PAs with numerous signals (10-, 20-, 40-, and 60-MHz long-term evolution signals) using different ADC sampling frequencies. The DPD with the under-sampling ADC could achieve comparable performances to its counterpart with a full-rate ADC, while using 3–5 times lower sampling frequency, and around $-{hbox{50-dBc}}$ adjacent channel power ratios were achieved.

Description: A 16-element phased-array receiver has been developed for advanced W-band automotive radars. The phased-array receiver is based on a single SiGe chip with RF beamforming capabilities, which is packaged using low-cost bond-wire techniques and attached to a 16-element linear microstrip array. The antenna results in a directivity of 29.3 dB and a gain of 28.0 dB at 77–81 GHz, and can be scanned to $pm {hbox{50}}^{circ}$ in the azimuth plane in $sim {hbox {1}}^{circ}$ steps. The packaging details are presented together with the steps taken to ensure a wideband impedance match and low coupling between the phased-array channels. Gain measurements done at 79 GHz agree well with simulations. The 16-element phased array receiver was used with a 2-element frequency-modulated continuous-wave transmitter at 76.5–77 GHz and high-resolution millimeter-wave images were obtained. The work shows that complex millimeter-wave phased arrays can be packaged using traditional bond-wire techniques, and can be a powerful solution for advanced automotive radars.

Description: This paper presents a hybrid radar system that incorporates a linear frequency-modulated continuous-wave (FMCW) mode and an interferometry mode for indoor human localization and life activity monitoring applications. The unique operating principle and signal processing method allow the radar to work at two different modes for different purposes. The FMCW mode is responsible for range detection while the interferometry mode is responsible for life activities (respiration, heart beat, body motion, and gesture) monitoring. Such cooperation is built on each mode's own strength. Beam scanning is employed to determine azimuth information, which enables the system to plot 360 $^{circ}$ 2-D maps on which the room layout and objects' location can be clearly identified. Additionally, the transmitted chirp signal is coherent in phase, which is very sensitive to physiological motion and allows the proposed technique to distinguish human from nearby stationary clutters even when the human subjects are sitting still. Hence, the proposed radar is able to continuously track the location of individuals and monitor their life activities regardless of the complex indoor environment. A series of experiments have been carried out to demonstrate the proposed versatile life activity monitoring system.

Description: A compact 680-GHz waveguide orthomode transducer (OMT) and circular horn combination has been designed, tested, and characterized in a radar transceiver's duplexer. The duplexing capability is implemented by a hybrid waveguide quasi optical solution, combining a linear polarization OMT and an external grating polarizer. Isolation between the OMT's orthogonal ports' flanges was measured with a vector network analyzer to exceed 33 dB over a $〉$ 10% bandwidth between 630 and 710 GHz. Calibrated Y-factor measurements using a mixer attached to the OMT ports reveal losses through the transmit and receive paths that sum to an average of 4.7 dB of two-way loss over 660–690 GHz. This is consistent with radar sensitivity measurements comparing the new OMT/horn with a quasi-optical wire grid beam splitter. Moreover, the radar performance assessment validates the OMT as a suitable compact substitute of the wire grid for the JPL's short-range 680-GHz imaging radar.

Description: This paper presents the design of two combined linear power amplifiers for 7-GHz microwave backhaul, realized in 0.25- $mu$ m GaN on SiC monolithic technology. Both modules are based on a combined class-AB structure conceived for maximum back-off efficiency and reduced phase distortion, which are important requirements in backhaul systems. Different second harmonic loads are exploited in the two power amplifiers, leading to different performance in terms of output power, bandwidth and efficiency. The two stages exhibit a saturated output power in excess of 35 and 36 dBm on 16% and 26% of fractional bandwidth, respectively; moreover, the measured average efficiency in the presence of modulated signals with 7.4-dB peak-to-average power ratio is 18% and 25%. Simulations and experimental results demonstrate that the second-harmonic load has little influence on the linearity of the proposed amplifiers. Compliance with the spectrum emission mask defined for the targeted application has been achieved through low-order polynomial digital predistortion, thus demonstrating the high linearity of the stages. A comparison with a Doherty amplifier realized in the same technology and for the same application shows that the two proposed stages need a simpler predistorter to achieve the linearity required by standard specifications.

Description: A simple equivalent circuit model with empirical equations describing the peripheral feeding ports of conical-line power combiners is presented. The model allows the entire structure to be designed using transverse electromagnetic circuit theory without the need for any full-wave simulations. A summary of the model extraction process is given and the accuracy of the proposed model is confirmed by favorable comparisons with full-wave simulations. The circuit based design method is used to design a compact conical-line combiner showing measured performance similar to the current state of the art combiners in this technology, while being significantly smaller.

Description: A new microwave device called the cascaded type of coupled resonator decoupling network (C-CRDN) is proposed in this paper. The four-port device can be used to reduce the interference between two radio systems that work in adjacent or even contiguous frequency bands. A C-CRDN is cascaded between the two antennas to be decoupled and the I/O ports of their radio systems, respectively. The coupling matrix of a C-CRDN can be designed to meet the required isolation and return-loss specifications. To prove the concept, a fourth- and sixth-order C-CRDN using coaxial combline cavities are designed, fabricated, and measured according to the characteristics of a testing array that consists of two high-gain sleeve dipoles working in the adjacent time-division long-term evolution and wireless fidelity bands. The measured results have demonstrated that the proposed C-CRDN can effectively mitigate the coexistence interference between the two collocated systems by providing at least 20-dB isolation improvement and enhanced matching performance. The proposed technique is general and can find many applications in heterogeneous wireless systems.

Description: Wireless body area network (WBAN) applications benefit extensively from the advantages offered by unique features of ultra-wideband (UWB) wireless communication, such as high data rate, low power consumption, and simple transmitter design. A major disadvantage in using UWB for WBAN applications is the complexities introduced by UWB receivers, such as high power consumption, poor receiver performance due to low sensitivity, and complex hardware implementation. This paper presents hardware implementation of a new communication system, where UWB is used for high data-rate transmission from sensor nodes and a 433-MHz industrial, scientific, and medical (ISM) band receiver is used for receiving low data-rate control messages at the sensor nodes. A full network system for WBAN applications has been implemented including a unique medium access control protocol. The proposed WBAN system is designed to dynamically control the pulses per bit value used for the UWB data communication using control messages received via the narrowband feedback link (i.e., the 433-MHz ISM link). This leads to dynamic bit error rate (BER) and power control at the sensor nodes, which improves the reliability of communication and power efficiency of sensor nodes under dynamic channel conditions. The performance of the system is evaluated in terms of BER, sensor initialization delay, and power consumption. This novel dual-band architecture utilizes the unique advantages offered by UWB communication and narrowband technology to enable high data rate, low-complexity hardware design, low power consumption, and small form factor for WBAN sensor systems.

Description: For predictive simulation of high-speed electronic components, an accurate and numerically efficient hot electron transport model is solved simultaneously with Maxwell's full-wave vector field equations. The transport model is based on ideal Fermi gas kinetics and incorporates electronic band structure as well as the essential electron scattering mechanisms. It couples self-consistently to full-wave electromagnetics through a field discretization scheme based on the relationship between Delaunay and Voronoi meshes. Three-dimensional simulations of different GaAs transistor designs produce dc and high-frequency results that compare well with measured data.

Description: Accurate admittance-transformer (Y-TF) feeds along with short-circuited stub-embedded resonators (SCSERs) are proposed in this study to design the improved parallel coupled-line (PCL) filters with structure-inherent transmission zeros (TZs). The proposed Y-TF feeds for flexible terminations are thoroughly analyzed and found more accurate than conventional approximate tapped-line feedings. Specifically, two basic parallel-coupled bandpass filters with conventional $lambda/2$ stepped-impedance resonators are first successfully implemented to validate the proposed Y-TF feedings. The ideal frequency responses of the two filters by a circuit simulator are compared with those transformed from the coupling matrix. Furthermore, an SCSER-based filter with multiple TZs is designed to verify the feasibility of the described design procedure. The adopted resonating components are composed of two short-circuited stepped-impedance stubs and multiple open-circuited ones all extended from a common joining point. The interstage couplings of the filter are achieved by the short-ended PCLs, while the input/output couplings are realized by the proposed Y-TF feedings. Through the fabrication of the proposed filters, the measured results along with the simulated ones validate the theoretical derivations.

Description: Analysis and applications of coupled cross-shaped resonator (CCSR) for fixed and fully reconfigurable differential bandpass filters (BPFs) design are focused in this paper. CCSRs with open and capacitive terminations are presented and discussed. One differential BPF named Filter I centered at 4.5 GHz with fixed differential-mode (DM) and common-mode (CM) responses using CCSR with open termination; and another one named Filter II using capacitive termination and loaded lumped capacitors offers fully reconfigurable DM center frequency, bandwidth and intuitive CM suppression control are proposed with very compact size $(0.01lambda_{0}^{2})$ . Such that ultra-wide DM center frequency tuning range of 82% fractional tuning range with both constant absolute bandwidth (ABW) and constant fractional bandwidth (FBW), easy control of CM suppression level and rejected range are achieved, respectively. Their experimental characterizations are in good agreement with theoretical analysis validating a simple approach of fixed and fully reconfigurable differential BPFs design.

Description: Compact planar crossovers with a wide passband are proposed. By cascoding two quarter-wavelength branch-line couplers, a wide passband can be obtained. Moreover, the even-odd mode and the fourfold symmetry are adopted to derive the analytical equations. According to the derived formulas, the transmission lines' impedances $Z_{1}$ , $Z_{2}$ , and $Z_{A}$ , which may influence the performance of the operating fractional bandwidth (FBW), should be properly selected. In terms of experimental verification, the circuit size of the fabricated crossover is $0.23lambda_{g}times 0.23lambda_{g}$ . Moreover, the FBW of the developed crossover is the 59% 1-dB insertion-loss relative bandwidth corresponds to the $S_{31}$ parameter, whereas the 55% 15-dB one refers to the $S_{21}$ parameter. In addition, four bandstop filters can be added at four ports of the proposed crossover to achieve a wide stopband performance.

Description: This paper presents a fully integrated eight-way power-combining amplifier for 110–134-GHz applications in an advanced 90-nm silicon–germanium HBT technology. The eight-way amplifier is implemented using four-stage common-emitter single-ended power amplifiers (PAs) as building blocks, and reactive $lambda /4$ impedance transformation networks are used for power combining. The single-ended PA breakout has a small-signal gain of 20 dB at 116 GHz, and saturation output power ( $ { P}_{rm sat}$ ) of 12.5–13.8 dBm at 114–130 GHz. The eight-way power-combining PA achieves a small-signal gain of 15 dB at 116 GHz, and $ { P}_{rm sat}$ of 20–20.8 dBm at 114–126 GHz with a power-added efficiency of 7.6%–6.3%. The eight-way amplifier occupies 4.95 $ {hbox {mm}}^{2}$ (including pads) and consumes a maximum current of 980 mA from a 1.6-V supply. To our knowledge, this is the highest power silicon-based D-band amplifier to date.

Description: This paper reports on two power amplifier (PA) monolithic microwave integrated circuits (MMICs) operating at frequencies around 220 GHz. The PAs use 250-nm InP HBTs and thin-film microstrip technology formed with a benzocyclobutene dielectric. Both PAs utilize a two-emitter-finger HBT unit-cell with each finger having an emitter area of ${hbox{0.25}}times {hbox{6}}~mu{hbox {m}}^{2}$ . The single-stage amplifier MMIC has six two-emitter HBTs in parallel for a total emitter area of ${hbox{18}}~mu{hbox {m}}^{2}$ . This amplifier has $sim {hbox {5 dB}}$ of small-signal gain from 210 to 230 GHz. It has demonstrated saturated output power of 90 mW at 210 and power-added efficiency (PAE) of 10%. This is the highest PAE number demonstrated at these frequencies. The two-stage PA uses three single-stage PAs, one as a driver and two in a balanced configuration in the second stage. The total output emitter area is ${hbox{18}}~mu{hbox {m}}^{2}$ . This PA demonstrated saturated output $〉{hbox {100 mW}}$ and PAE $geq {hbox{4}}{%}$ from 210 to 225 GHz.

Description: Accurately modeling the memory effects is critical in modeling and nonlinearity pre-compensation for wideband radio frequency (RF) power amplifiers (PAs) with strong memory effects. In this paper, the memory effects are divided into two categories: lagging memory effect and leading memory effect, which are defined based on the input samples located after and before the current output samples, separately. Considering the above two types of memory effects, a generalized two-box cascaded (GTBC) nonlinear behavioral model for RF PAs with strong memory effects is proposed: one box for a static nonlinearity block that is used to include the strong static nonlinearities and the other box for a dynamic nonlinearity block which is used to predict the mild dynamic nonlinearities. The modeling accuracy of the proposed model, in terms of the normalized mean square error (NMSE) and the memory effect intensity (MEI), is compared to the generalized memory polynomial (GMP), the augmented Hammerstein (AH) and the enhanced Hammerstein (EH) models for a 450–470 MHz Doherty PA with a three-carrier WCMDA input signal and a 895–935 MHz inverse Class-F Doherty PA with a single-carrier FDD-LTE OFDM input signal. The validation demonstrates that the proposed model leads to high-accuracy with fewer modeling coefficients and floating point operations (FLOPs).

Description: Two novel adaptive steady-state criteria are proposed to adaptively determine whether the steady state has been achieved in finite-difference time-domain (FDTD) method. The proposed criteria are established by the total electromagnetic energy in the computational region. To reduce the computational burden of electromagnetic energy calculation, a new approach is presented to replace the volume integral of energy with a surface integral. In addition, after newly defined attenuation coefficient and stability coefficient, novel adaptive steady-state criteria are proposed to overcome the premature convergence, nonmonotonicity, and nonconvergence challenges, which are serious in traditional adaptive steady-state criteria. At the end of this paper, numerical examples are given to demonstrate the effectiveness and superiority of our proposed criteria.

Description: This paper presents a divide-by-4 (D4) and divide-by-8 (D8) regenerative frequency dividers (RFDs) with the quadrature and the octet outputs. The topologies of the D4 and D8 RFDs use the even-harmonic mixers and the current-mode-logic (CML) loop dividers to achieve high division ratio and wide locking ranges. The modified Gilbert cells with quadrature- and octet-phases local-oscillator switching transistors are adopted to perform 2 $times$ and 4 $times$ subharmonic mixing with good conversion efficiency. The divide-by-2 and D4 CML loop dividers are used to obtain wide frequency range and the quadrature and the octet outputs. The D4 and D8 RFDs were fabricated by using a 90-nm CMOS process. With consuming 10.8 and 17.8 mW of dc power, the measured locking ranges of the D4 and D8 dividers are 13.2–18.4 and 16.8–26 GHz, respectively. Over the whole locking range, the two dividers with the phase deviation between the quadrature and the octet signals to be less than 2.2 $^{circ}$ and 4.4 $^{circ}$ , respectively. The proposed circuits achieve wide locking ranges and accurate output phases, making them very attractive for application into a multi-phase generator.

Description: A theoretical comparison of fundamental limitations on the output power of balanced diode mixers and even harmonic mixers is presented in this paper. The modulator operation is employed for the formulation. Additionally, the maximum output power, the output power at the 1-dB gain compression point, and the conversion loss of both mixers are formulated. It is theoretically confirmed that even harmonic mixers exhibit output power saturation when there is a high local oscillator power, although balanced diode mixers exhibit no saturation. This saturation is caused by restrictions in the built-in voltage of diodes, and even harmonic mixers therefore have lower output power capability when compared to balanced diode mixers. Derived formulas are confirmed by performing experimental investigations at 100 MHz.

Description: Dielectric spectroscopy (DS) is an important technique for scientific and technological investigations in various areas. DS sensitivity and operating frequency ranges are critical for many applications, including lab-on-chip development where sample volumes are small with a wide range of dynamic processes to probe. In this work, we present the design and operation considerations of radio-frequency (RF) interferometers that are based on power-dividers (PDs) and quadrature-hybrids (QHs). Such interferometers are proposed to address the sensitivity and frequency tuning challenges of current DS techniques. Verified algorithms together with mathematical models are presented to quantify material properties from scattering parameters for three common transmission line sensing structures, i.e., coplanar waveguides (CPWs), conductor-backed CPWs, and microstrip lines. A high-sensitivity and stable QH-based interferometer is demonstrated by measuring glucose–water solution at a concentration level that is ten times lower than some recent RF sensors while our sample volume is $sim$ 1 nL. Composition analysis of ternary mixture solutions are also demonstrated with a PD-based interferometer. Further work is needed to address issues like system automation, model improvement at high frequencies, and interferometer scaling.

Description: An analytical formulation for relative dielectric constant retrieval is reconstructed to establish a relationship between the response of a spiral microstrip resonator and effective relative dielectric constant of a lossy superstrate, such as biological tissue. To do so, an analytical equation is modified by constructing functions for the two unknowns, the filling factor $A$ and effective length $l_{rm eff}$ of the resonator. This is done by simulating the resonator with digital phantoms of varying permittivity. The values of $A$ and $l_{{rm eff}}$ are determined for each phantom from the resulting S-parameter response, using particle swarm optimization. Multiple nonlinear regression is applied to produce equations for $A$ and $l_{{rm eff}}$ , expressed as a function of frequency and the phantom's relative dielectric constant. These equations are combined to form a new nonlinear analytical equation, which is then solved using the Newton–Raphson iterative method, for both simulations and measurements of physical phantoms. To verify the reconstructed dielectric constant, the dielectric properties of the physical phantoms are determined with commercial high temperature open-ended coaxial probe. The dielectric properties are reconstructed by the described method, with less than 3.67% error with respect to the measurements.

Description: This paper reports a full-rate direct decision-feedback-equalization (DFE) receiver with circuit techniques to widen the data eye opening with competitive power and area efficiencies. Specifically, a current-reuse active-inductor (AI) linear equalizer is merged into a clocked-one-tap DFE core for joint-elimination of pre-cursor and long-tail post-cursors. Unlike the passive-inductor designs that are bulky and untunable, the AI linear equalizer offers orthogonally tunable low- and high-frequency de-emphasis. The clocked-one-tap DFE resolves the first post-cursor via return-to-zero feedback data patterns for sharper data transition (i.e., horizontal eye opening), and is followed by a D-flip-flop slicer to maximize the data height (i.e., vertical eye opening). A 10-Gb/s DFE receiver was fabricated in 65-nm CMOS. Measured over an 84-cm printed circuit board differential trace with 23.3-dB channel loss at Nyquist frequency (5 GHz), the achieved figure-of-merit is 0.027 pJ/bit/dB (power consumption/date rate/channel loss). At 10 $^{-12}$ bit error rate under ${hbox{2}}^{7}-{hbox{1}}$ pseudorandom binary sequence, the horizontal and vertical eye opening are 59.6% and 189.3 mV, respectively. The die size is 0.002 mm $^{2}$ .

Description: This paper presents an unilateralization technique for distributed amplifiers (DAs) based on the transformer coupling between the gate and drain lines. Theoretical analysis of the DA indicates that the voltage waves in the gate and drain lines can be described by a system of linear partial differential equations. The transformer coupling between the lines allows for cancellation of the reverse transmission coefficient of the system. There is an optimal value for the coupling coefficient between the lines that unilateralizes the DA. This optimal coupling coefficient is derived in terms of the gate–drain capacitance and capacitances of the gate and drain lines. Using the proposed technique, two monolithic microwave integrated circuit DAs are designed and implemented in a 0.1- $mu{hbox {m}}$ GaAs pHEMT process. The first DA provides average gain of 10 dB and 3-dB bandwidth (BW) of 39 GHz. The amplifier exhibits the minimum noise figure (NF) of 2.3 dB and the maximum output 1-dB compression point $({ P}_{1 {rm {dB}}})$ of 14.0 dBm, while consuming 80 mW from a 2-V supply. The second amplifier, composed of two cascaded coupled-line DAs, provides average gain of 19.2 dB, 3-dB BW of 37.5 GHz, the minimum NF of 2.3 dB, and the maximum ${ P}_{1 {rm {dB}}}$ of 12.6 dBm. It consumes 131 mW from a 2-V supply. The designed amplifiers can operate with supply voltages as low as 0.5 V to reduce power consumption, while their gain, BW, and NF are preserved. The maximum ratio of gain-bandwidth product to power consumption ${rm GBW/P}_{rm dc}$ of 11.9 GHz/mW is provided by the cascaded DA.

Description: This paper presents a fully integrated 5.8-GHz dedicated short-range communication transceiver with a 10- $mu{hbox {A}}$ interference-aware wake-up receiver (WuRx) for Chinese electronic toll collection system terminals that can operate with a low standby and operating current consumption. To reduce the current consumption, a high-gain RF envelope detector using a voltage-boosting method is proposed for both the WuRx and receiver (Rx) while the proposed high-power ASK modulator extends output dynamic range in low power consumption. Additionally, a delay-based bandpass filter is adopted in the WuRx to filter out interference from automotive applications, thus increasing the battery lifetime by reducing the probability of a false wake-up. The proposed transceiver is fabricated using 0.13- $mu{hbox {m}}$ CMOS technology with a chip size of 2.8 ${hbox {mm}}^{2}$ for the target frequency range of 5.8 GHz. The measured results demonstrate sensitivities of $-$ 44 and $-$ 61 dBm for the WuRx and Rx, dissipating currents of 10 $mu{hbox {A}}$ and 19 mA from 3.3-V supply voltage, respectively. The transmitter exhibits a normal output power of $+$ 5 dBm at an operating current of 46 mA.

Description: A methodology for the harmonic-balance analysis and design of rotary-traveling wave oscillator is presented. Two different implementations are compared. The first one is the standard configuration based on a distributed transmission lines. The second one is a new configuration based on a differential nonlinear transmission line (NLTL), which enables the generation of square waveforms with reduced number of stages, while still maintaining the capability to produce multiphase signals. The possible coexistence of oscillation modes is investigated with a detailed bifurcation analysis versus practical parameters such as the device bias voltage. The phase-noise spectrum is predicted from the variance of the common phase deviation. The parameters that determine this variance are identified with the conversion-matrix approach. The two prototypes, based on a distributed transmission line and a differential NLTL, have been manufactured and characterized experimentally, obtaining very good agreement between simulations and measurements.

Description: A new design methodology is presented for the planar implementation of a classical Marchand balun. A novel intuitive analysis shows that the Marchand configuration can be designed optimally to eliminate the phenomenon of “trace separation,” which is frequently observed in planar implementations. The new theory shows that this unbalancing effect is caused by the parasitic transmission line formed between the inner strip and ground, which is not considered in Marchand's original coaxial structures. Compact design equations are derived, based on which a new innovative structure is proposed and fabricated. This demonstrates the elimination of trace separation and achieves flat equal port split over a double octave bandwidth, performing up to 10 GHz, using an industry standard single-layer thin-film process having a continuous unpatterned ground plane. Popular planar variants of Marchand's original structures are also designed and fabricated to verify the new design equations. These structures are compared in terms of bandwidth, trace separation, and balanced port impedances.

Description: Describes the above-named upcoming special issue or section. May include topics to be covered or calls for papers.

Description: This paper reports the first LC voltage-controlled oscillator (LC-VCO) in CMOS utilizing a novel nontraditional compact inductor with integrated vertical nano particles magnetic core (Ni–Zn–Cu) to improve the figure-of-merit (FOM) of the VCO circuit. The new magnetic-enhanced inductor, fabricated in an integrated-circuit back-end using a CMOS-compatible process, improves inductance density ( $L$ -density) and quality factor ( $Q$ -factor) up to 7 GHz. A 1.36–1.86-GHz VCO with a nano-ferrite-integrated inductor was fabricated in a 180-nm RF CMOS. Measurements show that the magnetic-cored inductor improves the $L$ -density and $Q$ -factor by 49.8% and 59.2% at 1.8 GHz, respectively, while reducing the size by 26%. The VCO achieves reduced power consumption of 2.7 mW at a 1.8-V supply, low phase noise of less than $-{hbox{121}}$ , and $-{hbox{126 dBc/Hz}} $ at 100-kHz and 1-MHz frequencies offset, and a high FOM of 202 dBc/Hz. This prototype VCO demonstrates that the new vertical-nano-magnetic-cored inductor technology is a potential solution to high-performance low-cost compact RF systems-on-chip.

Description: Millimeter-precision meter-distance real-time indoor ranging capability is challenging due to multipath reflections in a rich scattering environment. Traditional continuous wave (CW) phase-based ranging methods, although simple and flexible, are vulnerable to phase offsets and interferences. We improve the previous CW approach by passive broadband harmonic nonlinear-transmission-line (NLTL) tags. Since phase information is now contained within the second harmonic rather than the fundamental frequency, interferences and phase errors caused by direct reflections of the interrogating signal are greatly reduced. By the broadband property of NLTL, a heuristic multi-frequency CW method is formulated to resolve the phase integer ambiguity and to further improve ranging accuracy and robustness even under large phase errors. We present theoretical and simulation analyses, followed by experimental verification.

Description: In this paper, a symmetric four-port microwave varactor based 90 $^{circ}$ directional coupler with tunable coupling ratios and reconfigurable responses is presented. The proposed coupler is designed based on the modified structure of a crossover, where varactors are loaded. By applying suitable biasing voltages to the varactors, the power-dividing ratios between the two output ports (i.e., port 2 and port 3) of the coupler can be easily controlled. Moreover, it is found that the realizable power ratio using the proposed structure is very flexible (it could be extremely large or small). Therefore, under the special case when the coupling ratio is tuned to be 1, the proposed coupler is reconfigured to be a crossover. Good isolation and return-loss performance have been maintained for different power-dividing ratios. To theoretically analyze the proposed device, closed-form design equations are derived using the even–odd mode method. Based on these analytical equations, an experimental prototype working at 1 GHz is designed, fabricated, and characterized. The measurement results match well with the simulation and theoretical results, validating the proposed design theory.

Description: By adding a complex isolation component between two 90 $^{circ}$ transmission lines at an arbitrary phase angle from the input terminal, a small Wilkinson power divider provides physical separation and electrical isolation between two output ports. General design equations for the complex isolation component are derived from even- and odd-mode analysis. Parallel and series RLC circuits are chosen to realize complex isolation components, respectively. Considering the bandwidths of $S_{22}$ , $S_{33}$ , and $S_{32}$ , inductors in both parallel and series RLC components are omitted to get the widest bandwidths; mathematical proof and design examples are also presented in this paper. A coupled line section with a compensating capacitor is introduced to reduce the circuit size, where characteristic impedances between even and odd mode are different in the coupled line section, and their electrical lengths are also different in inhomogeneous medium. Mathematical equations and simulation examples prove that the compensating capacitor compensates the characteristic impedance difference in the homogeneous medium and the electrical length difference in the inhomogeneous medium. Finally, an experimental circuit shows good agreement with the theoretical simulation.

Description: Two- and four-pole 0.7–1.1-GHz tunable bandpass-to-bandstop filters with bandwidth control are presented. The bandpass-to-bandstop transformation and the bandwidth control are achieved by adjusting the coupling coefficients in an asymmetrically loaded microstrip resonator. The source/load and input/output coupling coefficients are controlled using an RF microelectromechanical systems (RF MEMS) switch and a series coupling varactor, respectively. The two- and four-pole filters are built on a Duroid substrate with $varepsilon_{ r}=6.15$ and $h=25 {hbox{mil}}$ . The tuning for the center frequency and the bandwidth is done using silicon varactor diodes, and RF MEMS switches are used for the bandpass-to-bandstop transformation. In the bandpass mode of the two-pole filter, a center frequency tuning of 0.78–1.10 GHz is achieved with a tunable 1-dB bandwidth of 68–120 MHz at 0.95 GHz. The rejection level of the two-pole bandstop mode is higher than 30 dB. The bandpass mode in the four-pole filter has a center frequency tuning of 0.76–1.08 GHz and a tunable 1-dB bandwidth of 64–115 MHz at 0.94 GHz. The rejection level of the four-pole bandstop mode is larger than 40 dB. The application areas are in wideband cognitive radios under high interference environments.

Description: In this paper, we present design and analysis of an innovative low-jitter low-phase-noise 10-GHz sub-harmonically injection-locked phase-locked loop (PLL) with self-aligned delay-locked loop in 65-nm CMOS technology. With the proposed innovative topology, the phase between the injection signal and the voltage-controlled oscillator in the PLL can be dynamically aligned to minimize the jitter over the variations. A modified theoretical model of the sub-harmonically injection-locked PLL with self-aligned injection is developed for the design methodology. The in-band phase noise of the sub-harmonically injection-locked PLL can be significantly improved using the self-aligned sub-harmonically injection-locked technique. The design considerations of the locking range, loop bandwidth, and frequency division ratio are addressed. At 10 GHz, the measured phase noise of the proposed PLL with self-aligned injection at 1-MHz offset is $-$ 130.2 dBc/Hz with a root-mean-square jitter of 44 fs. The total dc power consumption is 62.7 mW. From ${hbox{10}} ^{circ}{hbox{C}}$ to ${hbox{70}} ^{circ}{hbox{C}}$ , the measured phase noise at 1-MHz offset and jitter are better than $-{hbox{129 dBc/Hz}}$ and 48 fs, respectively. This work demonstrates excellent performance and good robustness over the variations, and it can be compared to the previously reported state-of-the-art sub-harmonically injection-locked PLLs.

Description: We demonstrate direct quadrature modulator and demodulator monolithic microwave integrated circuits for future terahertz communications at 300 GHz based on the quadrature phase-shift keying (QPSK) modulation format. For the modulating and demodulating signal, we employed half-Gilbert cell mixers, which provide balanced signaling and moderate performance in conversion efficiency with a simple circuit configuration. In order to maintain the balance performance of the modulator and demodulator, passive baluns and couplers are implemented with thin-film microstrip lines, which exhibit less insertion loss than inverted microstrip lines (IMSLs), while the active mixers are based on IMSLs for short interconnections. The half-Gilbert-cell mixers have a wide enough operation bandwidth for high-throughput communications of more than 10% at 300 GHz. According to the static constellation of the modulator, imbalance is expected to be less than approximately $pm {hbox{0.6 dB}} angle {hbox {4}}^{circ}$ . A nonchip back-to-back experiment was conducted at up to 60 Gb/s, and 50-Gb/s operation was verified with a low bit error rate on the order of ${hbox{10}}^{-8}$ or less. The results demonstrate that the QPSK modulation scheme can be applied to double the data rate at terahertz frequencies.

Description: We present, for the first time, an efficient adjoint variable method (AVM) for estimating second-order sensitivities exploiting time-domain transmission-line modeling. For a structure with ${mbi n}$ designable parameters, the complete Hessian matrix of any desired objective function is estimated using ${mbi n}$ extra simulations as compared to $O({mbi n}^2)$ using the traditional finite-difference approaches. Our approach is illustrated through estimating the second-order sensitivities for energy functions and scattering parameter with respect to dimensions and material properties of metallic and dielectric discontinuities. The results achieved using our AVM approach are verified using the expensive finite-difference approaches.

Description: This paper presents, for the first time, the design and implementation of a planar tunable crossover. This crossover is derived from the conventional two-section branch-line crossover by substituting its three vertical transmission lines with the two fixed capacitors and one tunable capacitor to realize the tunable passband. By designing its horizontal transmission lines as coupled lines and replacing its vertical transmission lines by three capacitors, the circuit size is greatly reduced. Closed-form equations for design parameters are derived to simplify design procedure of the proposed crossover. For verification, a crossover with tunable frequency of 1.2–2.4 GHz is designed based on the given design closed-form equations. Finally, a microstrip tunable crossover with one varactor diode 1sv277 is fabricated and measured. The measured results are in good agreement with the simulated ones. The results show that the passband can be tuned in a frequency range from 1.29 to 2.06 GHz, yielding 46% tuning range with better than 20-dB return loss and isolation, while the insertion loss varies from 0.59 to 1.22 dB. The crossover occupies a small size of $0.25 lambda{ g} times 0.04 lambda { g}$ , which is only 8% of the area of conventional two-section branch-line crossover.

Description: This paper presents a novel method for designing Gysel power dividers with arbitrary power-division ratios as well as filtering responses. A coupling structure is utilized to replace the quarter-wavelength microstrip line in the power divider. By altering the coupling strength, the power ratio can be arbitrarily controlled with the highest ratio of 10:1. Furthermore, the coupling structures enable the filtering function of the power divider. Two transmission zeros are created near the passband edges, resulting in high-selectivity quasi-elliptic responses. Theoretical analysis is carried out, and closed-form equations are derived based on circuit theory and transmission line theory. For demonstration, three filtering Gysel power dividers are implemented with different power-division ratios (1:1, 3:1, and 10:1). In all of these circuits, power splitting and bandpass filtering functions are observed with good performance. Comparisons of the measured and simulated results are presented to verify the theoretical predications.

Description: The stopbands of microstrip filters were extended by additional stubs to alter the resonant frequencies of the 2nd and 3rd harmonics, making the resonators stagger tuned. The stubs also change the voltage distributions in the resonators, modifying the coupling coefficients. Equations for estimating the frequency shifts are given, and the operating principle of the voltage redistributions is discussed. Harmonics were suppressed to better than $-$ 34 dB in measured filters with 22%, 15%, and 8% bandwidth, with no measurable increase in passband attenuation.

Description: A compact single-layer substrate integrated waveguide (SIW) monopulse network for $Ku$ -band tracking system applications is investigated and demonstrated in this work. The feeding network and the monopulse comparator are integrated into a substrate with a structure size of $8.2lambda_{0}times 9lambda_{0}$ at center frequency while 32 output ports are welded perpendicularly for connecting active transmit/receive modules. The optimal design of a 3-dB coupler with metallic slots and phase shifter with dual steps is presented. The relative frequency bandwidth ( $vert{ S}11vert$ , $vert{ S}22vert$ , and $vert{ S}33vert〈10 {hbox {dB}}$ ) of the network is 6%, in which the phase imbalance of all ports is less than 5.5° [root mean square (rms)], the power imbalance is about 0.5 dB (rms). The insertion losses are about 3–5 dB and the isolations between the three channels are all better than 25 dB. The good performances of this SIW-based monopulse network are validated by measurements, showing the advantages of low cost, light weight, easy fabrication, etc. It presents an excellent candidate for $Ku$ -band tracking systems or up-band millimeter-wave systems.

Description: A class of dual-band bandpass filters (BPFs) have been exactly synthesized and practically designed by an equivalent circuit formed by a modified transversal array and its related filtering function. Either open- or short-circuited stepped-impedance resonators (SIRs) are mutually coupled as the basic filter block. By the Richard's transformation, the even-/odd-mode bisection circuits are made equal to their corresponding LC circuits. Combining these two parts together, an equivalent circuit of the proposed dual-band filter is obtained, which consists of a transversal structure and a $Pi$ -shaped inductor/capacitor network. With the addition of this $Pi$ -shaped network as the source-load coupling circuit, transmission zeros (TZs) can be generated on both sides of the desired passband to further improve the out-of-band rejection. To model and synthesize this class of equivalent circuit, a generic filtering function is derived by introducing a new filtering design parameter $varepsilon_{o}$ , namely, the out-of-band rejection factor. With the use of $varepsilon_{o}$ , the filtering function is modified to have a controllable out-of-band rejection while the bandwidth and TZ location of the filter are fixed. Two filter prototypes with open- and short-circuited SIRs are synthesized, designed, and fabricated in the last part to have supported both the proposed filter structure and the filtering design principle.

Description: We have successfully developed high-efficiency and high-power microwave amplifiers using a GaN field-effect transistor (FET) on a low-resistivity (LR) Si substrate for the first time. By introducing the LR Si substrate whose resistivity is less sensitive over temperature, the efficiency characteristics in high-temperature operation were significantly improved. In order to overcome the RF loss increase due to the utilization of the LR Si substrate, we have optimized the device structure of the FET by using an RC loss model accounting for drain-to-source capacitance $(C_{rm ds})$ and substrate resistance. High-efficiency characteristics were realized by optimizing the buffer structure and electrode structure. Furthermore, we have investigated efficiency improvement by second harmonic termination. The developed single-ended amplifier realized the saturation output power $(P_{rm sat})$ of 54 dBm, the linear gain (GL) of 19 dB, and the high efficiency of 33.5% at 8-dB back-off output power level under a WCDMA signal condition of 2.14 GHz at 50-V operation. The inverted Doherty amplifier using a pair of the 250-W GaN FETs delivered the $P_{rm sat}$ of 57.3 dBm with the GL of 15.5 dB under a pulsed continuous wave signal condition of 2.14 GHz, and demonstrated the digital pre-distortion linearization characteristics with the high efficiency of 48% and the adjacent channel leakage power ratio of $-{hbox{55 dBc}}$ at 50 dBm. These results are comparable to the best performance among the ever reported GaN on SiC FET high-power amplifiers.

Description: A digitally assisted amplitude calibration technique suitable for wideband phase-locked loops (PLLs) is presented in this paper. By operating the voltage-controlled oscillator in the current-limited region with a tunable bias scheme, an amplitude control mechanism is incorporated in the PLL system for performance optimization. Due to the use of a sequential search algorithm for amplitude calibration, the risk of locking failure is alleviated while maintaining a reasonable settling time. Using a 65-nm CMOS process, a 5-GHz wideband PLL with the proposed amplitude calibration is fabricated for a demonstration. Within the phase-locked frequency range from 4.6 to 6 GHz, the experimental results indicate output power variations of less than 2 dB as the calibration function is activated. Operating at an output frequency of 5 GHz, the measured output power and phase noise at 1-MHz offset frequency are $-$ 3.63 dBm and $-$ 105.8 dBc/Hz, respectively.

Description: We present the design and experimental demonstration of a magnetic screen, which can pattern magnetic field into 256 programmable spots of small sub-wavelength dimension. A design methodology is outlined for designing a near-field plate to achieve a desired focus, and its implementation is discussed. Simulation using a full-wave electromagnetic solver clearly demonstrates focused magnetic field spots and that the presented structure has a stronger magnetic field compared with a conventional coil at the same focusing distance. A sample of thickness 2.1 mm with 16 layers, in which there are 32 unclosed loops for focusing on each of the eight layers and optimized guiding strips on the other eight layers, is fabricated and measured. The measurement results agree well with the simulation results. Finally, the response of the magnetic screen in the time domain is measured and computed showing the screen can be operated under pulse excitation. Such a device, capable of producing a programmable focused magnetic field, will find applications in biomedical devices, near-field imaging systems, data storage, and electromechanical actuators.

Description: This paper proposes a hybrid class-AB/class-B voltage-controlled oscillator (VCO) with low voltage, low power, and a wide tuning range. The class-AB VCO core is designed to ensure robust start-up of the class-B VCO core. Featuring a high-efficiency class-B VCO core, the combination of class-AB/class-B VCO cores consumes low dc power. Based on the proposed architecture, the fabricated 0.18- $mu{hbox {m}}$ CMOS VCO exhibits a measured tuning range of 25.6%. Operating at a low supply voltage of 0.75 V, the hybrid class-AB/class-B VCO cores consume a low total dc power of 2.4 mW. In this bias condition, the measured average value of phase noise for all frequency ranges is $-$ 101.4 dBc/Hz at 1-MHz offset from the carriers. Compared to recently published wide-tuning range VCOs, the proposed hybrid class-AB/class-B VCO simultaneously achieves a low supply voltage, a low dc power dissipation, and wide tuning range, leading to a good figure-of-merit including the tuning range $({rm FOM}_{ T})$ . In addition, the theories for analyzing the VCO are given in detail, and the mechanisms are validated by experiments.

Description: A digitally modulated CMOS power amplifier (DPA) for a polar transmitter with a high dynamic range is presented. To improve local oscillator (LO) leakage, which limits the minimum output power of the DPA, the unit amplifier cell of the DPA employs a balanced mixer-type LO canceller at the power stage and a virtual ground is introduced in the layout of the output-power combining networks. A high dynamic range of the output power is simply achieved by adjusting gate-bias voltage of a cascode transistor in each power amplifier (PA) cell using a digitally controlled bias generator. This architecture allows a few-mA drain current at a low Tx power level without degrading the linearity. An array of unit PA cells is segmented to have a 10-bit amplitude resolution, and the bias generator is designed to have 8-bit control of the average output power. The peak output power is 24.4 dBm with an overall efficiency of 43% at 800 MHz. The total output dynamic range is 102.8 dB. A simple static pre-distortion helps the DPA achieve an average efficiency of 35% with a root mean square error vector magnitude of 3.59% while delivering linear output power of 22 dBm for WCDMA. The range of the digital transmit-power control for the WCDMA signal is 49.7 dB. This chip is fabricated in a 65-nm RF CMOS process.

Description: This paper presents a linear Doherty power amplifier (PA) with enhanced back-off efficiency mode for handset applications. For linear Doherty operation, we analyze the gain modulation as well as the cancellation of the third-order intermodulation distortion in order to improve the linearity. A compact design method is also discussed to implement on a single chip for a handset. The proposed Doherty PA delivers good performance with regard to the third-generation (3G)/fourth-generation (4G) modulation signals. A switched-load power-mode PA is adopted in the proposed Doherty PA to enhance the efficiency in the low-power region with over 10-dB back-off. For demonstration purposes, the PA is implemented using an InGaP/GaAs heterojunction bipolar transistor and AlGaAs/InGaAs pseudomorphic high electron-mobility transistor process. The PA is tested at 1.85 GHz using both a long-term evolution signal with 16-quadrature amplitude modulation, 7.5-dB peak-to-average power ratio, and 10-MHz bandwidth (BW) and a wideband code division multiple access signal with 3.3-dB PAPR and 3.84-MHz BW. The proposed linear Doherty PA with an enhanced back-off efficiency mode delivers good performance in both the high- and low-power modes, implying that the dual-power-mode Doherty PA configuration can be a promising candidate for extending the battery life of handheld devices in 3G and 4G wireless communication systems.

Description: For application in radiometry or noise measurement systems, an integrated active hot–cold load (AHCL) operating in the $W$ -band (75–110 GHz) is presented and realized as monolithic millimeter-wave integrated circuit (MMIC). It makes use of a novel circuit topology that employs only a single active noise source and monolithic integrated switches to provide a cold and a hot noise reference temperature. The AHCL provides a measured cold temperature of only 230 K and a hot temperature of 860 K around 94 GHz, thus enabling two-point radiometric calibration and absolute power measurements. The noise source of the AHCL has been fabricated as a two-port test structure too. In that configuration, it has been measured as a low-noise amplifier with a noise figure of 2.5 dB at 94 GHz proving its good noise performance. As a standalone active cold load (ACL), an excellent noise power of only 190 K at 93 GHz is achieved. The AHCL and ACL MMICs have been fabricated in 100-nm gate-length metamorphic high electron-mobility transistor technology.

Description: This paper presents an analog circuit scheme to steer phased-array receivers in the direction of an incoming signal. The proposed circuit technique utilizes a coupled-oscillator array along with a coupled-phased-locked loop to auto-align an N-element receive array towards the direction of the incident RF signal. A four-element receiver array is implemented in 45-nm CMOS SOI process and achieves auto-steering range of $pm 35^{circ}$ from broadside. A three-element version of the array demonstrates higher auto-steering angle covering $pm 70^{circ}$ range. The receiver also performs signal demodulation for the incident modulated RF signal, allowing high-data rate communication. A 60-Mbps 64-QAM modulated RF signal is demodulated with error-vector-magnitude (EVM) less than 4% across the steering angle range. The chip area is 3.45 mm $^{2}$ including a pad frame with 30-mW/element power consumption. To the best of authors' knowledge, this is the first demonstration of an analog self-steering array in an integrated circuit.

Description: In this paper, the MOS transistor (MOST) moderate-inversion (MI)–weak-inversion (WI) region is shown to be the optimum design zone for CMOS 2.4-GHz common-source low-noise amplifiers (CS-LNAs) focused on low power consumption applications. This statement is supported by a systematic study where the MOST is analyzed in all-inversion regions using an exhaustive CS-LNA noise-figure (NF)–power-consumption optimization technique with power gain constraint. Effects of bias choke resistance and MOST capacitances are carefully included in the study to obtain more accurate results, especially for the MI–WI region. NF, power consumption, and gain versus the inversion region are described with design space maps, providing the designer with a deep insight of their tradeoffs. The Pareto-optimal design frontier obtained by calculation—showing the MI–WI region as the optimum design zone—is reverified by extensive electrical simulations of a high number of designs. Finally, one 90-nm 2.4-GHz CS-LNA Pareto optimal design is implemented. It achieves the best figure of merit considering under-milliwatt CS-LNAs published designs, consuming 684 $mu{hbox{W}}$ , an NF of 4.36 dB, a power gain of 9.7 dB, and a third-order intermodulation intercept point of ${-}{hbox{4 }}$ dBm with load and source resistances of 50 $Omega$ .

Description: This paper proposes a new class of multisine excitations that allows efficient characterization of nonlinear circuits. By offsetting the frequency of tones, one can distinguish between different intermodulation products in a multisine response. This property leads to many applications for nonlinear circuit characterization, such as in-band distortion measurements, memory effects characterization, and model performance assessment. Some applications are highlighted in this paper, focusing especially on the characterization of memory effects. The effectiveness of the approach is demonstrated with a series of measurement results.

Description: This paper presents a novel power amplifier (PA) architecture for amplifying dual-carrier signals with simultaneous high efficiency and high linearity. This dual-carrier PA is based on two high-efficiency PAs and an innovative RF carrier combiner, which is a diplexer implemented with bandstop filters (BSFs). This special BSF diplexer is capable of combining two carriers with ultra-narrow frequency spacings, e.g., down to 0.25% fractional bandwidth, while maintaining a low combining loss of $〈$ 1 dB. Compared to conventional diplexers implemented with bandpass filters, this new technology leads to minimized resource usage for achieving the same combining performance. The integrated PA exhibits excellent performance when amplifying dual-carrier signals in terms of linearity and efficiency. Specifically, third-order intermodulations of $〈$ 40 dBc were measured with 70.2% (60.8%) power-added efficiency for carrier spacing of 10 MHz (5 MHz).

Description: This paper compares on-wafer thru-reflect-line (TRL) and off-wafer short-open-load-thru (SOLT) and line-reflect-reflect-match (LRRM) vector-network-analyzer probe-tip calibrations for amplifier characterization and parasitic-extraction calibrations for transistor characterization on silicon integrated circuits at millimeter-wave frequencies. We show that on-wafer calibrations generally outperform off-wafer and LRRM probe-tip calibrations at millimeter-wave frequencies. However, certain parasitic-extraction algorithms designed specifically to remove contact pads, transmission-lines, and access vias correct for much of the error in off-wafer calibrations.

Description: This paper proposes a new dual-band baseband equivalent (BBE) Volterra model devised to predict the behavior of dual-band power amplifiers (PAs) and/or to linearize their response. A series of derivations were applied to the original continuous passband Volterra-series expression to uncover a simple formulation that related the BBE envelopes of the output signals in each band to those at the input in the discrete domain. This yielded an inherently low-complexity dual-band Volterra-series model that does not require the empirical pruning commonly applied to the low-pass equivalent Volterra series. The proposed model was successfully applied to digitally predistort and linearize a dual-band 45-W class-AB GaN PA driven with different dual-band dual-standard test signals. For each band, the model necessitated less than 25 coefficients to reduce the adjacent channel leakage power ratio ACLR by up to 25 dB.

Description: This paper, for the first time, analyzes in detail the kink phenomenon in ${ S}_{22}$ as observed in GaN HEMT technology. To gain a comprehensive understanding, the kink effect (KE) is studied with respect to temperature and bias conditions. The achieved results clearly show that the dependence of the KE on the operating condition should be mainly ascribed to the transconductance, which plays a determinant role in the appearance of this effect. Furthermore, the analysis is extended to investigate the peak in the magnitude of ${ h}_{21}$ showing its disappearance at low drain–source voltage, due to the increase of the intrinsic output conductance. The importance of this investigation originates from the fact that an accurate and complete characterization of these anomalous phenomena enables microwave engineers to properly take them into account during the modeling and design phases.

Description: In this paper, a new type of microwave microfluidic sensor is proposed to detect and determine the dielectric properties of common liquids. The technique is based on perturbation theory, in which the resonant frequency and quality factor of the microwave resonator depend on the dielectric properties of the resonator. A microstrip split-ring resonator with two gaps is adopted for the design of the sensors (i.e., a double split-ring resonator). This resonator is both compact and planar, making it suitable for a lab-on-a-chip approach. Several types of solvents are tested with two types of capillaries to verify sensor performance. At 3 GHz, very good agreement is demonstrated between simulated and measured results.

Description: The measurement of complex permittivity of materials is of significant importance in scientific research and industrial applications. In this paper, we introduce the strongly coupled magnetic resonance previously used in high-efficiency midrange wireless power transfer to the noncontact measurement of the complex permittivity of materials. Theoretical analysis, full-wave simulation, and experimental measurements will show that the introduced high- ${ Q}$ -factor resonance can be used to effectively improve both the measurement sensitivity and the impedance matching to the instrument, avoiding the major weaknesses of the traditional magnetic induction method. The measurement setup can be easily calibrated for both solid and liquid materials and can provide the flexibility in noncontact measurement at a variable distance. We expect a wide range of applications to emerge from this novel approach.

Description: In this paper, we explore the accuracy limits of a finite-element time-domain (TD) method applied to the Maxwell equations, based on a discontinuous Galerkin scheme in space, and a leap-frog temporal integration. The dispersion and dissipation properties of the method are investigated, as well as the anisotropy of the errors. The results of this novel analysis are represented in a practical and comprehensible manner, useful for the application of the method, and for the understanding of the behavior of the errors in discontinuous Gelerkin TD methods. A comparison with the finite-difference TD method, in terms of computational cost, is also included.

Description: In this paper, a novel planar bandpass filter is proposed, designed, and implemented with a hybrid structure of substrate integrated waveguide (SIW) and coplanar waveguide (CPW), which has the advantages of good passband and stopband performance inherited from SIW and miniaturized size accompanying with the CPW. Additional design flexibility is introduced by the hybrid structure for efficiently controlling the mixed electric and magnetic coupling, and then planar bandpass filters with controllable transmission zeros and quasi-elliptic response can be achieved. Several prototypes with single and dual SIW cavities are fabricated. The measured results verified the performance of the proposed planar bandpass filters, such as low passband insertion loss, sharp roll-off characteristics at transition band, etc.

Description: This paper presents a tunable bandpass filter with a reconfigurable-pole response. 2-, 3-, and 4-pole states can be obtained based on employing series resonators with RF switches. The synthesis for the proposed filter is established, and the bandwidth for each pole state can be selected based on theory. The filter is built on a Duroid substrate with $varepsilon_{ r}=10.2$ and $h=25 {hbox{mil}}$ . The tuning for the center frequency is done using Schottky diodes, and the selection of the filter poles is achieved using RF microelectromechanical systems switches. A tuning of 0.73–1.03 GHz is achieved with a 1-dB fractional bandwidth of 3.9%–5.2%. The rejection levels at 200-MHz offset frequency of 2-, 3-, and 4-pole states are 28, 36, and 45 dB, respectively. This filter topology can find applications in reconfigurable radios with dynamic rejection levels.

Description: This paper reports the RF packaging design for electrooptic modulators operating in the millimeter-wave domain and discusses the RF and optical performances of the module. An ${hbox{LiNbO}}_{3}$ phase modulator has been integrated in a compact housing offering a 1.0-mm RF coaxial input connector. A coplanar waveguide on a low dielectric-loss alumina substrate has been designed to transition the RF field from the connector to the modulator. A RF insertion loss in the 1–2.5-dB range has been measured for the module over the 70–110-GHz bandwidth. A half-wave voltage comprised between 8.6 V at dc and 20 V at 110 GHz was calculated based on the observation of the optical modulation sidebands over the entire 110-GHz bandwidth. The optical insertion loss of the module was measured at 2.8 dB.

Description: This paper addresses noise and sensitivity issues in remote sensing and detection of vital signs based on a continuous wave biomedical radar operating at multiple harmonic carrier frequencies or channels. This Doppler radar makes use of a single mixer, taking advantage of the inherent nonlinearity and harmonic characteristics of the mixer. Other system building elements such as antennas, amplifiers, and circulators can also operate at and comply with multiple harmonic frequencies or channels requirements, which makes the system compact. Noise is one of the most important factors that affect the sensitivity of this type of system. The total noise is the combined contribution of thermal noise, residual phase noise, and flicker noise. Flicker noise is found to be the critical parameter for the baseband detection. Experimental results show that with the use of the harmonic radar technique, the flicker noise can be reduced by 20 dB around 1-Hz baseband frequency compared with the counterpart in a conventional radar operating at single frequency. The noise and sensitivity of a harmonic radar system operating at 12 and 24 GHz for vital signs detection are studied theoretically and experimentally. It is proven that the harmonic radar solution is able to increase detection sensitivity by increasing the signal-to-noise ratio. The performance of the harmonic radar is tested experimentally with a moving plate and also a real patient. For the heartbeat detection, an oximeter giving the oxygen saturation of blood and heart rate is used as the reference.

Description: A fully model-based nonlinear embedding device model including low- and high-frequency dispersion effects is implemented for the Angelov device model and successfully demonstrated for load modulation power-amplifier (PA) applications. Using this nonlinear embedding device model, any desired PA mode of operation at the current source plane can be projected to the external reference planes to synthesize the required multi-harmonic source and load terminations. A 2-D identification of the intrinsic PA operation modes is performed first at the current source reference planes. For intrinsic modes defined without lossy parasitics, most of the required source impedance terminations will exhibit a substantial negative resistance after projection to the external reference planes. These terminations can then be implemented by active harmonic injection at the input. It is verified experimentally for a 15-W GaN HEMT class-AB mode that, using the second harmonic injection synthesized by the embedding device model at the input, yields an improved drain efficiency of up to 5% in agreement with the simulation. A figure-of-merit is also introduced to evaluate the efficacy of the nonlinear embedding PA design methodology in achieving the targeted intrinsic mode operation given the model accuracy.

Description: The two major challenges associated with the conversion of a wireless system operating in air to an implantable version, antenna detuning and biocompatibility, are addressed in a coherent way. An RF identification (RFID)-based biomedical telemetry system designed for free-space operation was chosen as the starting reference. A new pin-compatible space-saving antenna with a ground plane was designed, fabricated, and tested to replace the original “free-space” antenna in the active RFID tag without making any other changes to the tag circuit, such that the tag would function well when it is placed under rat skin and fat. Biocompatibility and potential antenna detuning due to rat tissue variations were addressed in the design process, without significantly increasing the tag physical height, by applying a thin coating of biocompatible material directly over the antenna. The operation of the medical telemetry system was successfully demonstrated, with the tag placed under rat skin and fat, and its range of 60–72 cm was found to be sufficient to support medical research experiments conducted with rats in cages. Due to the biocompatible coating over the antenna, antenna matching is very insensitive to changes in tissue dielectric constants and thickness. The footprint of the new antenna is 33% less than that of the original antenna, its measured 10-dB return-loss bandwidth is 100 MHz or 11%, and overall efficiency is 0.82% at 920 MHz.