A 24 GHz Microwave Sensor With Built-in Calibration Capability Designed in MMIC Technology

A microwave sensor realized in monolithic technology, intended for permittivity estimation with the use of a highly sensitive coupled-line section, is presented in this paper. It also contains a dedicated measurement circuitry realized as a five-port correlator, therefore, a simple scalar power measurement can be utilized to obtain vector signal corresponding to the measured material without the usage of an external vector network analyzer. To suppress systematic measurement errors arising from the manufactured circuit's imperfections it is equipped with an integrated calibration block, the parameters of which can be simply tuned with two biasing voltages. The sensor is calibrated following a recently reported procedure, which requires neither known nor specific calibration values, in contrast to other methods with much stronger constraints. It is shown for the first time, that a measurement system incorporating a multiport correlator can be successfully calibrated with such arbitrarily chosen settings of the calibration block. To experimentally validate correctness of the calibration's convergence, the developed sensor is calibrated multiple times with different sets of the calibration block's settings, each time resulting in the same output values. It proves that the approach to calibration of measurement systems incorporating the multiport correlator can be significantly simplified with no impact on calibration accuracy. Finally, the measurement of the sensor's response for two dielectric samples clearly demonstrates the advantages of the utilized calibration.