Measurement of Distance down to Zero Meters by Standing Wave Radar

Various types of radars have been developed and used until now—such as Pulse, FM-CW, and Spread Spectrum. Additionally, another type of radar has been proposed recently. The radar measures distance by using standing wave and has been named as “Standing Wave Radar." Standing wave radar has a shorter minimum detectable range and higher accuracy compared to other types. However, the radar can not measure distance down to zero meters like other types of radars. Minimum detectable range of the standing wave radar depends on a usable frequency range. A wider frequency range is required if we need to measure shorter distance. We show a new method for measuring distance down to zero meters without expanding the frequency range. Specifically, we derive an analytic signal, which is a complex sinusoidal signal, by processing the signals obtained from multiple detectors, and we calculate and obtain distances by Fourier transform of the analytic signal. We then verify the validity of our method by simulations based on numerical calculation. The results show that it is possible to measure distance down to zero meters. In our method, measurement errors are caused by gain deviation of the detectors. They are several cm if the gain deviations are less than ±1%. Prevalent radars still have a common defect that they can not measure distance from zero to the minimum detectable range. We expect that the defect will be eliminated by putting our method into practical use.