Ultra-Wideband, Compact, and High-Gain Two-Port Antenna System for Full-Duplex Applications

A broadband, dual-polarized, and common-aperture
$2\times 2$
cavity-backed slot antenna (CBSA) array for enabling full-duplex wireless communication is presented. The antenna consists of a thin rectangular cavity appropriately loaded with metallic septa to excite multiple resonances of similar desired field distribution to achieve consistent radiation characteristics over a wide bandwidth. Four pairs of concentric orthogonal radiating slots are cut out on one of the broad walls of the cavity all of which are fed by two concentric orthogonal slots on the opposite broad wall of the cavity. The cavity is fed by an end-launch coaxial-to-waveguide transition to excite one of the channels. The other channel is excited by a two-pronged microstrip line symmetrically crossing over the other cavity feeding slot. Due to the out-of-phase coupling from the two prongs of the microstrip line to the other port, this type of excitation is shown to provide an unprecedented level of isolation between the two channels over a wide bandwidth. To achieve a high-efficiency and fabrication accuracy of this complex architecture, the antenna is 3-D printed out of HP PA12 Nylon and is then metalized by the silver spraying technology. The fabricated antenna provides a minimum of 55 dB of isolation and 8 dB of return loss over 44% fractional bandwidth from 4.8 to 7.5 GHz. Keeping its size smaller than
$1.3 \lambda _{L} \times 1.3\lambda _{L} \times 0.27\lambda L$
(where
$\lambda _{L}$
is the free space wavelength at the lowest frequency), and its weight less than
$70g$
, the antenna provides a minimum gain of 10 dB for both polarizations and exhibits more than 20 dB polarization discrimination within the main beam over the entire band.