New Concept Zero-IF Receiver For Pulse Compression Radar Systems

Active remote sensing radars have a lot of applications, including agriculture, mapping and research of ocean ice. In recent years, active research showed great potential in vital sign detection and early tumor detection. For different applications, different requirements are set for the radar source, especially the waveform, working frequency and bandwidth, have strong influence on the detection performances. In this dissertation, the DDS technique is used to generate baseband signals, which are quadrature modulated with a local oscillator to get a radio-frequency output. The DDS based signal generator uses a FPGA based memory controller, a DDR DRAM high-speed data memory, and a high-speed digital to analog converter. It can generate arbitrary baseband signals with frequencies up to125MHz and chirp signals with bandwidth up to250MHz.Flicker noise and DC offset have strong impacts on the performance of zero-IF receivers. In this paper, we propose a generalized approach to eliminate such impacts on zero-IF architecture pulse compression radars. The conventional low-pass filter in a zero-IF receiver is replaced with a pre-defined filter, to filter out the DC and low-frequency components from the demodulated radar signal. Simulation and experimental results demonstrate that, based on the prior knowledge of the radar signal and the pre-defined filter, the performance degradation, due to the complete filtering of the low-frequency components, can be recovered through a newly deduced compensation equation. Our approach can be widely used in the implementation of highly integrated, high-performance pulse compression radar systems in the future.The propagation of electromagnetic waves in a medium is dictated by material dispersion. The negative group velocity is observed in the vicinity of plasma frequency. It is pointed out that the occurrence of the negative group velocity is due to the distortion of the dispersion surface, and its front velocity remains subluminal. This result validates the viewpoints of Sommerfeld and Brillouin, that the front velocity in any medium would never be faster than the speed of light in free space.