Real-time photonic detection of direction and chirp rate for blind microwave LFM signals

De-chirp reception serves as a fundamental technique for direction detection of linear frequency modulated (LFM) signals. However, precise estimation of the chirp rate is crucial to ensure accurate de-chirping and subsequent angular estimation. In this paper, a novel photonic scheme for the real-time direction detection and chirp rate estimation in blind microwave LFM signals with unknown chirp rates is proposed and experimentally demonstrated. The proposed system is mainly built by two parallel dual-drive Mach-Zehnder modulators (DDMZMs) with a specially designed antenna array, where a fixed delay is introduced at one terminal to preprocess its received signal. The delayed signal is evenly split to drive both DDMZMs in parallel, along with the received signals from two additional antennas. After photodetection and low-pass filtering, the desired low-frequency output signals can be obtained. By analyzing these signals, the required direction and chirp rate of the received blind LFM signals can be determined. Benefitting from the specified antenna configuration, the proposed scheme can simultaneously extract the chirp rate and direction of the blind LFM signals with better resolution and broader range. Experiment results demonstrate that the direction ranging from −85.5° to 76.6° with the error smaller than 2°, and the chirp rate with the error smaller than 1.8 Hz/ps can be achieved for the blind LFM signals across varying time-bandwidth product values.