A Portable 5.8 GHz Dual Circularly Polarized Interferometric Radar Sensor for Short-Range Motion Sensing

The conventional short-range interferometric radar sensors usually employ two separate transmitting (TX) and receiving (RX) antennas for improved TX-RX isolation. However, they are subject to increased system size and misalignment of the TX/RX radiation patterns. In this article, a portable 5.8 GHz dual circularly polarized (CP) interferometric radar sensor is presented, which leverages the proposed dual CP common-aperture antenna that reduces the size of the entire radar system. The common-aperture nature gets rid of the radiation pattern misalignment and ensures that the object can be in the optimal boresight direction. Cross polarization, i.e., right-hand CP (RHCP) for TX and left-hand CP (LHCP) for RX or vice versa, was employed based on the sequentially rotated array (SRA), which not only improves the TX-RX isolation but also adapts with the polarization change in radar sensing. Moreover, a near-field cancellation technique was proposed to further increase the TX-RX isolation in the small form factor. A portable 5.8 GHz radar sensor integrated with the proposed dual CP antenna was custom-designed. Compared to the conventional two-antenna architecture, the proposed radar sensor is reduced in size by 140% but can still achieve a high TX-RX isolation of >60 dB at 5.8 GHz. Experiments were carried and the results illustrate that the proposed radar sensor has high micrometer accuracy in detecting the predefined displacement motions and is able to precisely track the human vital signs in the office environment.