Characterization and Performance Measurement of Low RCS Wideband Circularly Polarized MIMO Antenna for Microwave Sensing Applications

This article presents a low radar cross section (RCS), compact wideband, circularly polarized, multiple-input-multiple-output (MIMO) antenna for microwave sensing and measurement applications in S-and $C$ -bands. The proposed antenna consists of a wide slot and an I-shaped protruding stub in the ground plane of the antenna. A U-shaped strip is incorporated between two microstrip feed lines to achieve high isolation between antenna elements and a low envelope correlation coefficient (ECC), which results in the improved performance of the microwave sensing and measurement system. An array of the square slot is created in the ground plane of the antenna, which further enhances the isolation between the antenna elements and also reduces the RCS of the proposed antenna. The latter is fabricated with a low-cost FR-4 substrate using a precision printed circuit board milling machine. The 10-dB impedance bandwidth of the proposed antenna is 88% (3.7–9 GHz) with the isolation of greater than 15 dB. The 3-dB axial ratio bandwidth (ARBW) of the antenna is 3.7–5.7 GHz. The proposed antenna demonstrates significant RCS reduction in the frequency range of 10–24 GHz when compared with the same size metallic plate. The ECC, diversity gain (DG), and total active reflection coefficient (TARC) are also evaluated to justify the diversity performance of the proposed MIMO antenna.