Ground Penetrating Radar (GPR) sections commonly suffer from strong scattered energy and weak reflectors, with distorted lateral continuity. This is mainly due to the gradual variation of moisture with depth, dense lateral sampling of common-offset GPR traces (which are considered as zero-offset data), along with the small wave-length of the electromagnetic (EM) waves which is comparable to the size of the shallow subsurface dielectric heterogeneities. Focusing of the diffractions requires efficient migration which, in the presence of highly heterogeneous subsurface formations, can be improved by a detailed migration velocity model. Such a velocity model is difficult to develop, since the common-offset antenna array is mostly used for its reduced time and cost in both the data acquisition and processing stages. In such cases, migration processes are based on limited information from velocity analysis of clear diffractions, cores or other ground truth knowledge, often leading to insufficient imaging. We propose a methodology to obtain GPR sections with focused diffractions that is based on multipath summation, using weighted stacking (summation) of constant velocity migrated sections over a predefined velocity range. The success of this method depends on the assignment of an appropriate weight, for each constant velocity migrated section to contribute to the final stack, and the optimal width of the velocity range used. Additionally, we introduce a post-multipath summation processing step, which consists of time-varying spectral whitening, to deal with the decrease of the dominant frequency due to attenuation effects and the additional degraded resolution expected by the constant migration summed images. This imaging strategy leads to GPR sections with sufficiently focused diffractions, enhancing both the lateral and the temporal resolution, without the need to explicitly build a migration velocity model.