Maintenance of broadband detection in photonic time-stretched coherent radar employing phase diversity.

Frequency response fluctuation in a radar system distorts the envelope of the output signal after matched filtering, thereby impairing its broadband detection performance. Simulations are made under various types and degrees of fluctuation. The results prove that the peak power and range resolution of broadband detection suffer different levels of deterioration. Moreover, simulation results also show that two outputs with orthogonal phase diversity have complementary variation trends and their combination can effectively enhance the broadband detection performance. Based on theoretical analysis, we employ the combination of two orthogonal phase diversity to achieve broadband detection in the photonic time-stretched coherent radar. Compared with using an ordinary modulator, a dual-output-Mach-Zehnder-modulator-based system makes the dispersion-penalty-induced frequency response fluctuation decrease by 9.7 dB. For single target detection, the peak power is increased by 6.7 dB and the range resolution is improved from 8.4 cm to 4.8 cm. For two-target detection, a 6-cm spatial interval is distinguished reliably.