A high-stable photonics-based linearly frequency-modulated (LFM) signal generation approach for radar applications is proposed and experimentally demonstrated. A broadband LFM signal is generated by a photonic frequency quadrupler consisting of a Mach-Zehnder modulator and a fiber Bragg grating (FBG)-based optical notch filter. The stability of the generated signal is improved by using modulator bias control, laser wavelength control, and FBG temperature control. An experiment is performed. A Ka-band LFM signal with an instantaneous bandwidth of 4 GHz is generated. Meanwhile, inverse synthetic aperture radar (ISAR) imaging and target distance measurement are implemented by using a generated 1-GHz bandwidth LFM signal. The LFM signal remains stable during the four-hour experiment.
Higher calibration accuracy is essential to W-band phased array antennas due to their short wavelength. However, the feed amplitude and phase of the antenna unit usually deviates from its theoretical value because of the production and assembly of the phased array antenna. For this reason, the antennas should be calibrated to guarantee their performance. In order to solve this practical problem, an amplitude and phase calibration method based on the space feed characteristics of T/R modules is proposed in this paper. The proposed method can achieve high-precision alignment of the auxiliary antenna and the center of the tested front, and meanwhile obtain the true amplitude-phase distribution of the W-band phased array antenna. The proposed method effectively realizes the precise beam pointing of the W-band phased array antenna.
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