A Compact, Broadband, Two-Port Slot Antenna System for Full-Duplex Applications

A broadband common-aperture, and dual-polarized sub-array of Cavity-Backed Slot Antenna (CBSA) with two ports having a very high level of isolation is presented in this paper. The antenna is designed for wideband full-duplex wireless communication and FMCW radar systems. The antenna is composed of a thin rectangular cavity on which four cross-slots are cut out for radiation. The radiating cross-slots are fed by two concentric orthogonal slots on the back wall of the cavity. One polarization is excited by an end-launch coaxial to waveguide transition which is used to excite the cavity through a feeding slot. A two-pronged microstrip line symmetrically crossing over another feeding slot, oriented orthogonal to the feeding slot, is used to excite the other polarization. The microstrip line is designed such that each prong would couple to the waveguide feed out-of-phase and as a result, a very high isolation level is achieved between channels over a very wide bandwidth. Designed to be compatible with metal 3D printing, the devised antenna is fabricated out of aluminum using Direct Metal Laser Sintering (DMLS) technology. This sub-array slot antenna with dimensions smaller than 1. 28 AL x 1. 28 AL x 0. 27 AL (where AL is the wavelength at the lowest frequency), provides a minimum gain of 10 dB for both channels and exhibits a polarization isolation better than 20 dB within the main beam and a channel isolation above 54 dB over 40% fractional bandwidth.