The document discusses applying azimuth phase coding (APC) techniques to suppress range ambiguities in multichannel synthetic aperture radar (SAR) systems. It finds that while APC does not produce a simple Doppler shift in multichannel SAR signals as it does in conventional systems, it can still provide improved ambiguity suppression. The level of suppression depends on factors like the azimuth antenna pattern, oversampling ratio, and number of receive channels. When applied to example high-resolution wide-swath SAR systems, the reflector-based design achieved 3-8 dB of suppression compared to 0.7 dB for the planar design.

1. Ambiguity Suppression by Azimuth Phase Coding in Multichannel SAR Systems Folie DLR - Institut für Hochfrequenztechnik und Radarsysteme F. Bordoni , M. Younis, G. Krieger IGARSS 2011, 24-29 July, Vancouver, Canada

4. Review of the APC Technique APC is a technique for range ambiguity suppression, conceived for conventional (1 Tx and 1 Rx) SAR systems [Dall, Kusk 2004] azimuth sample number, order of range ambiguity, APC shift-factor APC residual phase [Dal04] J. Dall, A. Kusk, “Azimuth Phase Coding for Range Ambiguity Suppression in SAR”, IGARSS 2004. @ round-trip delay APC modulation phase Tx pulse number 3) Azimuth filtering over the processing bandwidth APC demodulation phase APC is based on three main steps: 1) Azimuth, i.e. pulse to pulse, phase modulation on Tx 2) Azimuth phase demodulation on Rx

6. Application to Multichannel Systems MULTICHANNEL PROCESSING N Rx az. signals sampled at PRF APC residual phase: 1 2 N Multichannel SAR system: 1 transmitter, N receivers  The behavior of the APC changes when applied to a multichannel system APC residual phase: reconstructed multichannel signal sampled at PRF eff =N PRF: PRF << B p

7. APC & Reconstructed Multichannel Signal The APC residual phase has no more a linear trend versus the azimuth sample (pulse) number  no shift of the Spectrum  The residual phase a “stair” shape (< ≠> Doppler shift):  The ambiguity spectrum: , , PRF (uniform PRF*) *PRF matched to the antenna length and No. of apertures > regular sampling in azimuth results

12. HRWS (High-Resolution Wide-Swath) SAR System promoted by the German Aerospace Centre (DLR) conceived to obtain high resolution and wide swaths (1 m resolution, 70 km swath width in stripmap mode) Different Rx azimuth patterns & multichannel reconstruction HRWS SAR Multichannel Systems Planar system: currently adopted design Reflector system: alternative design option, studied in DLR Parameter Planar Reflector Orbit height [km] 520 745 Carrier frequency [GHz] 9.600 9.650 Tx/Rx antenna total length [m] 8.75 Paraboloid diameter (elev., az.) [m] 10, 12 Total number of feeds (elev., az.) 60, 10 No. of az. Rx channels 7 10 PRF [Hz] 1750 2792 Processed bandwidth [Hz] 6252 5946 Oversampling factor 1.960 4.696