Abstract
For future spaceborne synthetic aperture radar (SAR) missions, digital beamforming (DBF) on receive in elevation to form a sharp high receive beam will be adopted to improve the signal to noise ratio (SNR) level and suppress range ambiguities. However, in some special cases, range ambiguities may be received by grating lobes with the high receive beam gain, and range ambiguities would not be well suppressed and even may be increased. In this paper, a new receiving approach based on analog beamforming (ABF) and DBF is proposed. According to the spaceborne SAR imaging geometry and the selected pulse repetition frequency (PRF), the antenna patterns of all subapertures of the whole receive antenna in elevation are adjusted by ABF at first. Afterwards, signals from all subapertures in elevation are combined by a real time DBF processor onboard. Since grating lobes could be suppressed by the antenna pattern of the subapertures via ABF, range ambiguities would be well suppressed even if ambiguities are received by grating lobes. Simulation results validate the proposed approach.
Highlights
Future spaceborne synthetic aperture radar (SAR) systems require the high resolution wide swath imaging capacity [1,2,3]
In addition to overcoming the contradictive pulse repetition frequency (PRF) requirement, improving the signal to noise ratio (SNR) level and suppressing range ambiguities are very important for spaceborne high resolution wide swath imaging
To improve the SNR level and suppress range ambiguities, a large size of the planar receive antenna is adopted in elevation
Summary
Future spaceborne synthetic aperture radar (SAR) systems require the high resolution wide swath imaging capacity [1,2,3]. In addition to overcoming the contradictive PRF requirement, improving the signal to noise ratio (SNR) level and suppressing range ambiguities are very important for spaceborne high resolution wide swath imaging. Besides adopting the large size of the planar antenna with multiple subapertures, the large size of the reflector antenna is suggested for the DBF operation in elevation [10,11,12] This DBF on receive scheme is to form a narrow sharp receive beam which follows the radar pulse as it travels on the ground. In some special cases depending on the relationship between the operated PRF and the side looking SAR imaging geometry, parts of range ambiguities are received by grating lobes with the high antenna gain, which may result in the seriously increased range ambiguity to signal ratio (RASR).
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