Abstract
A frequency-domain system identification-based multiple-input multiple-output (FDSI-MIMO)-SAR algorithm using multiple phase center multiple azimuth beams is proposed to obtain high-resolution wide-swath (HRWS) imaging. Frequency-division multiple access is used in such a way that each transmitter emits a conventional linear frequency-modulated (LFM) waveform modulated by a different carrier frequency and the obtained range resolution corresponds to the total transmitted bandwidth. In this article, an MIMO-SAR problem is modeled, using the principle of displaced phase center, as multiple but separate multiple-input single-output (MISO) system identification problems. The channel impulse responses of the individual MISO problems are identified in the range dimension using an FDSI-based estimation algorithm in such a way that the estimated range profile is free of interrange cell interference. In addition, the proposed algorithm does not require separating the subband waveforms at the receiver as they are processed jointly without a need to add guard bands between the adjacent subbands, which would allow utilizing the available bandwidth to the maximum efficiency. The method of synthesizing a wide transmit antenna beam from a narrow antenna beam applied in single-input multiple-output (SIMO) SAR is extended to MIMO SAR to remove the sidelobes effects of the receive beams and hence leading to the desired signal-to-noise ratio. A pulse repetition frequency lower than the Doppler bandwidth is used to obtain wide swath without experiencing aliasing in the Doppler spectrum. Finally, both simulated and constructed raw data are used to validate the effectiveness of the proposed algorithm.
Highlights
S IMO SAR [1] and MIMO SAR [2] [3] [4] have been proposed to address the trade-off between the desired wide swath width and high cross-range resolution in conventional strip-map SAR
The following section shows the numerical results of our proposed frequency domain system identification (FDSI) estimation algorithm for MIMO SAR using a set of linear frequency modulated (LFM) waveforms and compares it with a conventional SISO SAR using an LFM waveform
The point spread function (PSF) of the proposed method is compared with the point spread function of the conventional LFM waveform to illustrate the free inter-range cell interference property as shown in Fig.3 in which the proposed method exhibits ideally a zero level side-lobes as the impulse response is measured directly unlike the case of the matched filter
Summary
MIMO SAR has been first introduced in [8] where it is stated that it is possible to obtain a high resolution wide swath image due to the extra phase centres introduced by the use of the multiple transmitters along with the multiple receiving channels. Multiple sub-band MIMO SAR emits multiple radar waveforms with different carrier frequencies simultaneously [7]. This would allow to increase the transmitted bandwidth significantly. An inter-range cell interference (IRCI) free based on cyclic prefix (CP) orthogonal frequency division multiplexing (OFDM) waveform is proposed in [16] but the use of cyclic prefix, which is removed at the receiver, does not allow the full utilisation of the transmitted energy.
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