Digital phased array architectures for radar and communications based on off-the-shelf wireless technologies

Abstract

This thesis is a continuation of the design and development of a three-dimensional 2.4 GHz digital phased array radar antenna. A commercial off-the-shelf quadrature modulator and demodulator were used as phase shifters in the digital transmit and receive arrays. The phase response characteristic of the demodulator was measured and the results show that the phase difference between the received phase and transmit phase is small. In order to increase the bandwidth of the phased array, a method of time-varying phase weights for linear frequency modulated signal was investigated. Using time-varying phase weights on transmit and receive give the best performance, but require the range information of the target. It is more practical to use time-varying phase weights on only one side (transmit or receive but not both), and constant phase weights on the other side. The simulation results showed that by using time-varying phase weights, the matched filter loss is not as severe as it is when using the conventional fixed weights technique. It was also found that this method is only effective for small scan angles when the time-bandwidth product is large. The approach to implement time-varying phase weights on transmit using commercial components such as direct digital synthesizer and quadrature modulator is discussed.