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The synthetic aperture radar (SAR) imaging relies on the coherent sum of the received signals. Consequently, phase shifts along the beamwidth and bandwidth of the antenna radiation pattern can have a relevant impact on the final image. Previous studies have focused on other sources of image quality degradation, such as antenna mispositioning, frequency uncertainty, or antenna gain pattern effect. This article demonstrates that the phase of the antenna radiation pattern plays a critical role in the quality of the computed electromagnetic images. For this purpose, three different situations have been analyzed: 1) the phase shift changes across the angular range; 2) the nonlinear phase displacement across the working frequency band; and 3) antenna phase center drift across the bandwidth. Systematic simulations have been carried out modeling these phase shifts for different antennas and enabling to establish rules of thumb for the thresholds in all of the previous cases.

This article presents a processing technique that mitigates the impact of positioning errors on the quality of the images retrieved using handheld (or portable) scanners based on synthetic aperture radar (SAR). These systems rely on the use of tracking systems to combine the information acquired at multiple positions to achieve high-resolution images. This is especially challenging at millimeter-wave (mmWave) frequencies in the absence of high-accuracy tracking systems external to the handheld scanner. To this end, the proposed technique employs a hybrid coherent–incoherent SAR processing method especially suited for mitigating the impact of positioning errors from tracking systems performing simultaneous localization and mapping (SLAM). The proposed technique was experimentally validated using a handheld scanner comprising a compact radar module and a tracking camera that performs SLAM. Results show that if fully coherent processing is used, the quality of the obtained images is greatly degraded, and if fully incoherent processing is considered, there is a significant resolution loss, which prevents accurately imaging the shape of the targets. In contrast, using the presented method, it is possible to successfully image the targets, mitigating the impact of positioning errors from the tracking camera.