This paper proposes a novel design of a software-defined matched filter (MF) for digital
receivers of synthetic aperture radar (SAR). The block diagram of the proposed receiver is
described in detail. The purpose of this filter is to produce a SAR pulse with higher compression
ratio (CR) and lower side lobe level (SLL) than that produced by the conventional
MF. The proposed design is based on the idea of time windowing of the SAR pulse to
construct the transfer function of the receiver filter. The shape of the proposed time-domain
window is optimized to achieve the filter design goals including the minimization of the
SLL and the realization of the target value of the CR. The transmitted SAR pulse is, first,
subjected to linear frequency modulation and then subjected to the optimized window. The
width (time duration) of the proposed window is divided into equal time intervals. The
proposed time-domain window is constructed as a sequential continuous piecewise linear
segments. The instantaneous value of the time-domain window at the start of each time
interval is optimized so as to achieve the optimization goals. The width of the time-domain
window is shown to be proportional to the width of the compressed pulse after optimization.
The number of the time intervals into which the time duration of the window is
divided is shown to have a significant effect on the optimization results. The particle swarm
optimization (PSO) technique is then applied to get the window shape that minimizes the
SLL for a specific predetermined value of the pulse CR. It is shown that the iterations of
the PSO are fastly convergent and that the applied algorithm is computationally efficient.
Also, it is shown that the desired value of the pulse CR is achieved with accuracy of 100%.
Moreover, the achieved SLLs are about − 65 dB , −90 dB , −114 dB , and −133 dB for pulse
CR of 5, 3, 2, and 1.5, respectively. Finally, for practical implementation of the introduced
SAR pulse processing technique, the proposed optimized window is placed as a building block in a software-defined receiver of the SAR system. |
