Signal Generating Techniques For Multi-Beam Phased Array

Radar and sonar systems are widely used in such applications, as environmental surveying/imaging and target positioning/detection. To test and calibrate receiving channel processing of a radar or sonar system in a laboratory environment one needs to emulate phased array receiving signals; to let a radar or sonar system transmit power toward a certain direction, one needs to generate phased array driving signals. Hence it is highly desired to develop phased array signal generating techniques. Particularly for practical systems with irregular array shape, large number of signal channels and signal waveform flexibility, designing and building a phased array signal generator is quite challenging.This thesis studies phased array signal generating techniques, in the context of multi-beam sonar systems, to emulate receiving signals or generate driving signals of a phased array of large channel number, with a low-cost, low-power and small-size design. Two approaches are developed:one based on a D flip-flop loop and the other based on a time-division multiplexing digital-to-analog converter (DAC). The D flip-flop loop-based approach adopts a loop circuit formed by multiple shift registers and inverters, generating multiple square-wave signals of equal time-delay/initial phase differences, which are then reshaped to sine waves via low-pass filtering. The effect of time-delay precision on the beamforming performance is also analyzed, and it is shown that when the clock frequency is high enough, it is feasible to combine multiple D flip-flop loops of different clock sources into a signal generator of even more channels. The time-division multiplexing DAC-based appraoch uses judiciously-designed timing signals to control a mutli-channel switch to demultiplex the DAC output into individual channel signals, which can also be reshaped via low-pass filtering.The above approaches are different from the traditional ones using one DAC for each indiviual channel, and can be readily realized as engineering devices. Testing results of the performances of a realized device, such as channel to channel phase and amplitude consistency, crosstalk in-between channels, phase and frequency errors between the output signals and the expected signals, demonstrate that the developed approaches can meet the need of design of a general multi-beam measurement system. When the number of signal channels is large, the development here has significant advantages in regard to cost, space and power required; the time-division multiplexing DAC-based approach has more flexibility in signal waveform design.Lastly, a few schemes for phased transmission of multiple simultaneous beams are discussed, for the purpose of high resolution imaging system design. Those approaches can improve the image update rates while maintaining high imaging resolution; in the meantime transmission power in-between pre-formed beams can be greatly suppressed.