A Duplexing Hybrid Slot Antenna Design With High Isolation for Short-Range Radar Detection and Identification Applications at 24 GHz Band

This article presents a duplexing hybrid antenna architecture for short-range radar systems with high isolation and low loss between the two transmitting (TX) and receiving (RX) ports. The antenna utilizes a single slot for common resonance shared by the two TX and RX port excitations. These two ports were constructed through two parallel microstrip lines crossing over the specified shaped slot. The feeding structures of these two microstrip feedings and the separation are optimally designed to ensure the mutual coupling signals out-of-phase, and therefore, the signal cancellation can be achieved, leading to a high isolation between these two ports. In this design, the slot length is
$0.92\lambda $
at 24.125 GHz, forming an equivalent short circuit at the other port. Given the initial design criteria, the design with the optimal isolation could readily be found by minimal full-wave simulations. Meanwhile, the equivalent circuit model was used to investigate the working principles and to improve the isolation bandwidth and impedance matching at the central frequency. The measured maximum isolation is 70 dB at 24.125 GHz. The RF front-end modules with TX and RX amplifiers are also integrated to validate its feasibility for the radar system application. The mechanisms to widen the isolation bandwidth are also addressed.