Fiber Delay For Phased Array Antenna System Performance Analysis And Design Realization

Phased array antenna (PAA) is an enabling technology in modern radar and communication systems. Phased array antennas offer many advantages including steering without physical movement, high scan flexibility in two dimensions, precise elemental phase and amplitude control to obtain low spatial sidelobes. Instead of microwave phase shifters, the optical true time delay lines based on the optical techniques have the properties of light weight and low volume, which especially adapt to the airborne application. Furthermore, the optical delay lines can provide the immunity to electromagnetic interference and the squint-free wide instantaneous bandwidth required in the high-performance radar systems. In this thesis, the characteristics related to the optical true time delay line have been analyzed first, then a 4-bit optical true-time-delay feeder incorporating an integrated electro-absorption modulation DFB laser for X-band phased array antennas has been implemented. Experiment results are in excellent agreement with our design criterions.The architecture of a binary fiber optic delay line composed of optical switches has been adopted to implement the system. The system provides 24 discrete delay increments for achieving 4bit resolution in setting the microwave phase front. The maximum time-delay error is less than 3ps. We use an integrated electro-absorption modulation (EAM) distributed feedback (DFB) laser as optical source. Compared to the electro-optic modulator, the electro-absorption modulator (EOM) provides higher signal-to-noise (SN) ratio. Since the EAM is easily monolithic integrated with DFB laser, the insertion loss of the system is less than that with electro-optic modulator. The complexity of the system is reduced as well. The implemented system provides smaller size than existing RF (Radio Frequency) delay lines.