Pulse Radar system and FMCW radar system have already been practically used in the society as the distance measurement systems utilizing radar beam while the industrial use of them is often limited by the conditions of the Radio Transmission Regulation that stipulates mainly the allowable range of the beam intensity and the sweep band in each country. In this paper, a method to measure a short distance even in the narrow-band width is proposed and it utilizes the circuit to mix the wave reflected by the object with a transmitted wave. And also an in-phase signal and a quadrature signal of those mixed waves are utilized. As a technical reference to support the availability of the method, a case study with RF circuit model using a diode model is presented here with showing the possible achievement of measurement error ±2mm or less in a short distance 2m or less in the simulated bandwidth of 76MHz in 24.15 GHz band.