$F$ -Band Differential Microstrip Patch Antenna Array and Waveguide to Differential Microstrip Line Transition for FMCW Radar Sensor

This paper describes a differential microstrip patch antenna array and a rectangular waveguide to coupled differential microstrip line transition operating at 122 GHz. The antenna array is realized in series-fed topology/architecture and is very suitable for MIMO radar applications. This on-board antenna provides a high antenna gain and radiation efficiency at millimeter-wave frequencies. The rectangular waveguide transition with low insertion loss offers the facilities to characterize the on-board antenna and can also be utilized in a radar system in combination with a horn antenna. The measured bandwidth of the antenna array is 7 GHz with a maximum gain of 12.98 dBi at 122 GHz. The waveguide transition has a bandwidth of 20 GHz at 10-dB return loss. Radar measurements were performed using radar sensors that were equipped with the developed antenna array as well as the waveguide transition in combination with horn antenna for comparison purposes. The radar measurement results with on-board antenna array show a good performance for detecting the range of the target.