Six-Port Receiver and Frequency Measurement for Radar Applications at 35 GHz

The application of six-port technology in the receiving part of a radar front-end is described in this contribution. This receiver allows measuring magnitude and phase of the radar signal without the need of down-conversion. According to the applications and the availability of the devices needed for assembling the prototype sensor, the frequency of operation was set to 35 GHz. The structure of the six-port as well as the calibration and measurement algorithms are described in detail. The accuracy of the phase measurement is 2-10 degrees depending on the power level of the signal. Another key element of the proposed radar sensor is a direct frequency counter. Using this circuit it is possible to measure the frequency of operation with a resolution of 20 bits within 120 microseconds. The accuracy of the distance reading of the radar is directly related to the accuracy of the frequency measurement and has reached 0.1 mm.