A 5.8GHz ISM Band Single Antenna with Coupling Structure for Full-Duplex Doppler Radar Sensing

In this paper, a linear polarized patch antenna coupled with a microstrip rat race coupler is proposed for Doppler radar sensing applications. The conventional Doppler radar sensing uses two separated transmitting (TX) and receiving (RX) antennas that are usually placed more than half wavelength away from each other to reduce their mutual coupling. However, the two separated antennas inevitably increases the system size, which makes it hard to be integrated into miniature products or portable devices. This paper presents a novel antenna that combines the TX and RX antennas together to reduce the size of the whole radar system. The proposed antenna was designed to operate at 5.8GHz with TX/RX isolation better than 35 dB. The antenna's aperture size was reduced by 140% compared to the conventional solution having similar isolation with two separated TX/RX antennas.