Metamaterial-Based Circularly Polarized Patch Antenna for cmWave Full-Duplex mMIMO

A wideband, dual-layer metamaterial-based patch antenna operating at 10 GHz is proposed for centimeter-wave full-duplex (FD) massive multiple-input multiple-output systems. Full-wave simulations reveal an effective and wide impedance bandwidth of over <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$19 \%(1.9 \text{GHz})$</tex>, spanning from 9.5 GHz to 11.4 GHz. The antenna achieves a gain of 5.5 dB with a radiation efficiency exceeding 98 %. The introduction of a specially designed L-shaped cutting slot enables high circular polarization (CP) purity, achieving an axial ratio of 0.6 dB at 10.25 GHz and better than 3 dB across a 1.3 GHz (13 %) bandwidth. The resulting pure CP antennas support the creation of cross-polarized Tx-Rx antenna element pairs for FD operation. An improvement in Tx-Rx isolation of better than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{1 0 ~ d B}$</tex> is observed, reducing mutual coupling to better than -40 dB with an element separation of 4.6 cm (1.5 wavelengths).