Short range radar sensor with six-port network and its applications

Abstract

A radar sensor with six-port network is proposed. The radar sensor is called ‘six-port radar sensor’. The MMIC type six-port network is designed using InGaP HBT process for minimization to generate DC offset voltages. Calibration method and process are proposed to obtain high accuracy in the radar sensor. The proposed method uses the calibration equations, which are derived from considering amplitude and phase errors resulting from both imperfections in the six-port network and different diode characteristics. Distance measurement shows that the six-port radar sensor can have high range accuracy in short range detection. The maximum detection error in the distance measurement is approximately 2 % from 0.5 m to 3 m. Tx leakage signal limits the maximum detectable range in the six-port radar sensor. A quasi circulator for obtaining high Tx leakage signal isolation is proposed to increase the maximum detectable range. The proposed circulator improves the receiving sensitivity of the radar sensor by 13 dB, and the maximum detectable range is increased from 1.5 m to 2.5 m with -10 dBm output power through a horn antenna. By using a MPA, measured distance can be increased. Measurement result shows that the sensor can detect to 3.75 m, which is the maximum range in the current measurement environment. The six-port radar sensor is proposed for simultaneous measurement of distance and relative dielectric permittivity. The dielectric permittivity profile is obtained by measuring complex reflection coefficients, which are simply calculated with DC output voltages from the six-port network. Amplitude errors of reflection coefficients are calibrated by the distance measurement. The dielectric permittivity profile and the distance information of a target are obtained with a 24 GHz six-port radar sensor. The size of the radar sensor is $3.6 \times 5.5 cm^2$, excluding a horn antenna and signal generator. The six-port radar sensor, which constitutes simple RF front-end usin...