The Research Of Several Topics In ISAR Imaging

Inverse Synthetic Aperture Radar (ISAR) is attracting more and more attention in the world, and is becoming a new research field in signal processing. This paper pays more attention to two problems in ISAR imaging, which are the research of Bistatic ISAR imaging and the phase imbalance compensation in ISAR quadrature demodulation.Traditionally, ISAR is monostatic, that is, one antenna is used for both transmitting and receiving signals. This configuration has several disadvantages on limited radar range and vulnerable feature in electronic warfare. These disadvantages can be overcome by Bistatic ISAR due to the separation of the transmitter and the receiver. After introducing the concept and advantages of Bistatic ISAR and then the mature techniques of monostatic ISAR imaging, we provide the mathematic model of Bistatic ISAR. As for the provided echo signal, after reasonable assumptions and rigorous mathematic derivation, we get the formula of Bistatic ISAR imaging and also formula of azimuth resolution. By comparing with the monostatic ISAR case, we find that, Bistatic ISAR can be basically equivalent to one monostatic ISAR which is located along the angle bisector of the bistatic angle. Therefore we can apply mature techniques and algorithm of monostatic ISAR to bistatic situation. Then we conduct simulation experiments. Assuming that the target has three kinds of moving behaviors which are only rotation, moving on azimuth and moving on range, Range-Doppler imaging algorithm is applied for ISAR imaging with translation compensation for the latter two cases. Simulation results validate our theory of Bistatic ISAR imaging and also the feasibility of applying the mature monostatic ISAR imaging algorithm, which is the classic Range-Doppler algorithm, to Bistatic ISAR imaging.I/Q channel imbalance in quadrature demodulation is one of the major concerns in the design of ISAR receivers. The amplitude and phase mismatches result in the additional mirror signal, which acts as a correlated interference superimposed on the desired signal and, hence, degrades the whole system's performance significantly. In this paper, we first analyze the effects of I/Q channels imbalance in detail, and focus on the relationship between the mirror signal and imbalance effect. Then a new digital method for phase imbalance compensation is proposed. The phase mismatch is adaptively estimated and compensated by optimizing the matched filtering results without requiring any testing signals or measurement circuits. The method is based on the principle that when the phase mismatch is compensated perfectly, the entropy of the range-resolved image will reach the minimum or the contrast will reach the maximum. In addition, the simulation results indicate that the I/Q phase mismatch can be effectively compensated during the normal operation of the ISAR receivers, even in the rapidly changing case, as long as a linear system model for the imbalance is valid.