Phase-Coded-Linear-Frequency-Modulated Waveform for a Low Cost High Resolution Radar System.

摘要

Low cost Radar Systems are difficult to realize due to their high peak: power requirement. High output power implies the need for unconventional and expensive power amplifiers such as magnetrons and travelling wave tubes. Peak: output power is reduced by increasing the pulse width of the transmitted signal with minimum output power obtained from a continuous waveform or infinite pulse width. However, the drawback to increasing the pulse width is deterioration in resolution. This thesis uses pulse compression to achieve the required resolution. It combines two compression schemes: phase modulation and frequency modulation. Phase modulation is used to reject ambiguous targets while frequency modulation is used to achieve the finest resolution. Convolution of the phase modulated and frequency modulated waveforms yields a waveform which has the fine resolution property of the frequency modulated signal and the ambiguous target rejection property of the phase modulated signal. Target detection is done by correlation, and both types of pulse compression schemes have an auto-correlation response which approximates a delta function. Convolution is the only scheme which preserves the delta function auto-correlation response of the resulting waveform upon combination of the frequency and phase modulated signals. The Radar System demonstrated in this thesis also has a speed detection capability and this can be used to separate moving targets from stationery ones. Measured target speed is directly proportional to the frequency (Doppler) shift caused by moving targets and is obtained in this thesis by observing the phase shift over successive echoes. Since serial Doppler processing is done on correlated values, it has a higher CNR at the Doppler frequency than parallel Doppler processing performed on the received signal.