Low Profile Orthomode Full-Duplex Antenna for Wearable Biomedical Communication

A low-profile monolayer dual-port orthomode antenna is presented for enhanced in-band full-duplex (IBFD) communication of wearable biomedical devices. The proposed antenna consists of a center patch surrounded by a complementary slot within a larger peripheral patch. The two ports, which are at opposite lateral sides in a coaxial configuration, are responsible for the Tx/Rx channels respectively. By implementing an asymmetric displacement from the geometric axis, an odd surface current mode is excited via Port 2 (Rx mode), while the even mode is achieved through Port 1 (Tx mode). This mode orthogonality implementation allows a high isolation of > 35 dB between Tx/Rx channels across the central frequency of 6 GHz without circuit elements. In addition, a −10 dB bandwidth of 280 MHz (4.7%) and 480 MHz (8%) is achieved for Port 1 and 2 respectively which supports stable communication channels. The antenna is verified to simultaneously support a unidirectional radiation pattern towards the broadside (Port 1) and a multidirectional hybrid radiation pattern (Port 2) composed of bidirectional
$y$
-pol radiation (120° and 60°) as well as broadside
$x$
-pol radiation. Both Tx/Rx channels achieve a large front-to-back ratio of > 15 dB. The free space characterization results agree well with the full-wave simulations. Furthermore, the odd/even modes are determined to be stable under local deformations and human loading effects. In conclusion, this monolayer orthomode full-duplex antenna is suitable for various wearable applications due to its low-profile, highly manufacturable design and robustness to environmental imperfections.