SAR image formation with embedded QPSK via LFM waveform guardbands

Quadrature phase shift keying (QPSK) modulation is embedded to transmit data to a communications receiver via the guardbands (and perhaps beyond) of a linear frequency modulated (LFM) signal for synthetic aperture radar (SAR). We show that the combined signal sharing the spectrum can be used to form SAR images, i.e., there's no need to filter out the communications signal in the radar receiver. The communications signal itself is used in the image formation. We investigate the effect of parameterizing radar signal to noise power ratio (SNR), radar power to communications power ratio (RCR), and LFM to communications bandwidth ratio (LCBR) to the images. We also look at the effect of shifting the communications carrier away from the LFM spectrum on the SAR image.