Ambiguity Suppression by Azimuth Phase Coding in Multichannel SAR Systems

Abstract

The current generation of spaceborne synthetic aperture radar (SAR) systems suffers from a tradeoff between the achievable spatial resolution and swath width. This has motivated intensive research both on more flexible SAR systems, using multiple transmit/receive channels, and on techniques for removing the ambiguities. Among these techniques, the azimuth phase coding (APC), recently proposed to suppress range ambiguities in conventional SAR systems, stands out for its negligible implementation complexity and its effectiveness for point and distributed ambiguities. This paper investigates the possibility of applying the APC technique to the new, forthcoming generation of multichannel SAR systems, based on digital beamforming on receive. The extension of APC to multichannel SAR systems is mathematically described. Specific merit figures are defined to quantify the APC performance. A numerical analysis is developed to characterize the influence on the APC behaviors of the main SAR system parameters. Finally, an example of APC performance is provided, by considering two multichannel SAR systems based on a planar and a reflector antenna. Index Terms-Azimuth phase coding (APC), digital beamforming (DBF), synthetic aperture radar (SAR).

A Performance Evaluation of SAR-GMTI Missions for Maritime Applications

“…Therefore, the performance is expected to degrade for the case of nonhomegeneous ambiguous returns, especially close to coastal areas. A way to circumvent these impairments is to consider a future SAR-GMTI mission concept exploiting azimuth phase coding (APC) in combination with digital beamforming, such that a high-resolution wide swath (HRWS) mode can be operated [36].…”

Ambiguity suppression by Azimuth Phase Coding in multichannel SAR systems

“…Here, a proper spectral combination of the signals at each channel allows retrieving the overall band of interest [3]. When the APC modulation/demodulation is applied, independent on the specific multichannel reconstruction approach, the azimuth signal on each single Rx channel experiences the same residual phases and Doppler shift, given by (1) and (2) no more a linear trend versus the azimuth sample number and the properties of APC are no more guaranteed [8]. This assertion could be better explained by considering, without loss of generality, a SAR system based on a planar array antenna, operating with a uniform PRF.…”

“…The APC modulation/demodulation produces the same residual phase, given by (1), on each of the N receivers. Thus, the residual phase on the reconstructed signal has a "stair-shape" [8]:…”

Improved Azimuth Multichannel SAR Imaging for Configurations With Redundant Measurements

“…However, this technique also poses restrictions on system configurations and observations. For optimum performance, the system parameters and operating pulse repetition frequency (PRF) should be strictly programmed in order to obtain a signal that is equivalently sampled as a single-aperture signal with the same effective sampling rate [7]- [10]. When the PRF deviates from the optimal sampling frequency, the DPCA system will generate nonuniform samples, leading to serious ambiguity in subsequent imaging step.…”