Band-Stop Behavior Vertically Extended Ground Isolator Based on Transmission Line Theory for IBFD TRx Decoupling Applications

This article presents decoupling methodologies enabling dual-polarized coupling suppression for fifth-generation (5G) sub-6 GHz transmit/receive (TRx) antenna arrays with novel antenna illumination topologies. The isolator comprises the proposed vertically extended bent ground wall, which acts like a multistage band-stop filter modeled as a transmission line, i.e., it has a different behavior from the typical wall structure. To consider dual-polarized multi-path isolations in reliable 5G integration scenarios, an antenna having a height of
$0.13\lambda $
at 3.5 GHz with dual (±45° slant) polarization and port isolation of 25 dB is devised. It was demonstrated that the proposed isolator could significantly suppress the direct and ground coupling between TRx, using the resonance proven by transmission line theory. Moreover, the isolator composite combined with an electromagnetic band-gap (EBG) can further improve their dual-polarized decoupling by removing the surface wave coupling. Two sets of 3.5 GHz
$1 \times 4$
antenna arrays with 45°-slant polarization and the proposed isolator composite were designed, manufactured, and measured for simultaneous decoupling of eight paths among the TRx antenna elements. Finally, the measured results reveal that the overall isolation level of the dual-polarized array configuration is approximately 70 dB with a height of
$0.14\lambda $
, maintaining the matching and port isolation conditions.