The Key Technologies In Optical True-time-delay Phased Array Receiver

The phased array radar has been widely used because of its higher speed of beam steering than traditional radar. However, it only works in relatively narrow bandwidth due to the aperture fill time, limiting the application in complex conditions in modern warfare. Combining with the microwave photonics, the optical phased array antenna system designed in this dissertation compensates the aperture fill time with optical true time delays and realizes the phase shift and the synthesis of microwave signals in optical domain. It increases the instantaneous bandwidth of the radar and eliminates the effect of beam squint. The dissertation discusses the design of the optical phased array systematically and the test results of our experimental demonstration, offering a valuable reference on the design and realization of such system.The impact on the beam pointing and gain caused by the phase and amplitude errors of the phase-shift network has been analyzed theoretically. The beam squint effect and the advantages brought by true time delay are explained with the beamforming theory. Besides, the essential radio over fiber (RoF) link is mathematically modeled. And figures of merit of the link are derived based on the analytical model. Also, the performance enhancement techniques for the link are introduced. Finally the design proposal and the optimization of parameters are put forward according to these theoretical analyses.The performance of the optical phased array is determined by the accuracy of the optical fiber delay line (OFDL). A novel high-precision optical delay fiber manufacture procedure with high reliability is proposed in this dissertation. An optical fiber polishing platform is designed along with the process of OFDL fabrication based on the platform. The length of optical fiber is precisely measured with a vector network analyzer (VNA). The resolution of the OFDL is 0.1 mm, limited by the VNA’s uncertainty of phase measurement at working frequency.Photonic-assisted time interleaving analog-to-digital conversion technique and the methods of channel mismatch estimation and correction are presented, realizing a directly sampling of the radar echo signal at radio frequency. The proposed technique is verified with experiment using a high-sampling rate oscilloscope. The experiment reaches a equivalent sampling rate of 40 GSa s-1 with four channel sampling parallelly. The signal-to-noise and distortion ratio (SINAD) is 40.3 dB and the spur-free dynamic rage (SFDR) is 57.6 dBc at 6.31 GHz. The ENOB of the ADC system is 6.4 bits, limited by the oscilloscope.The performance of our optical phased array antenna prototype is fully tested in 2-4 GHz. The worst RF gain, noise figure and third order SFDR of the all-optical RoF link are-39.5 dB,40.3 dB and 93.2 dB · Hz2/3, respectively. The insertion loss of the OFDL is calibrated to 7 dB. The maximum amplitude root-mean-square error (RMSE) of the OFDL is 0.55 dB and the maximum delay RMSE is 0.4 ps. The maximum beam pointing RMSE is 0.35° (beam scanning from -40° to 40°) excluding the fault state. The test results shows the OFDLs have good amplitude and phase accuracy, leading to high precision in beam pointing. In the same time, the optical phased array antenna system eliminates the beam squint effect and improves instantaneous bandwidth.