Reserch on the Coherent Phase Noise of Millimeter-Wave Doppler Radar
The phase noise is a very important index to wireless system, especially in millimeter-wave continuous wave radar systems. The phase noise of the signal, which is firstly leaked from transmitter and then mixed to intermediate frequency band by the local oscillator (Tx-IF), will worsen the sensitivity of supper heterodyne radar system used for Doppler velocity detection. In this paper, the coherent analysis is applied on the phase noise after nonlinear process, which shows that the phase noise of the Tx-IF is affected by those factors: the magnitude of the phase noise of the transmitter and that of the local oscillator, and the correlationship between each other. In practice, by reducing the phase noise of the transmitter and that of the local oscillator and ameliorating the correlationship of the two phase noises, the phase noise of the Tx-IF can be improved greatly. Such proposition is successfully applied in the design of a millimeter-wave Doppler radar working at 95 GHz. The experimental measurement shows that the sensitivity of this radar is better than -70 dBm.