Periodic filters for performance enhancement of millimeter-wave microstrip antenna arrays

In this paper, periodic filters have been employed to enhance the performance of microstrip antenna arrays in automotive radar sensors. An isolation of more than 45 dB has been measured between transmit and receive antenna arrays formed on the same substrate with a separation distance of only 40 mm between them. The isolation enhancement obtained is more than 15 dB. Also a gain enhancement of about 2 dB has been observed due to employment of these periodic filters. Since these periodic filters consist of circular openings etched on the ground plane of the antenna, there is no additional cost or fabrication effort associated with this technique. These openings act as periodic stop band filters to suppress surface waves propagating between the antenna arrays. Measured and computed isolation values agree well.