S-Band Compact Microstrip Full-Duplex Tx/Rx Patch Antenna With High Isolation

In this letter, a new design for two-port transmit/receive (Tx/Rx) full-duplex microstrip patch antenna for 4G and 4G advanced communication systems is introduced. The proposed duplex antenna consists of a single gear-shaped radiating patch for bidirectional radiation. The isolation between transmit and receive ports is achieved by using a frequency space filtering technique where two omega-shaped defected ground structure (DGS)-based bandpass filters (BPFs) are created at transmit and receive ports of the antenna. The antenna achieves a compact size of
$\ ({{\text{70} \times \text{70}}})\text{ mm}^\text{2}$
, high isolation larger than
$ - \text{36}\;\text{dB}$
at the transmit frequency
${{f}_{t}} = \text{3.3}\;\text{GHz}$
and larger than
$ - \text{45}\;\text{dB}$
at the receive frequency
${{f}_{r}} = \text{3.215}\;\text{GHz},$
and small Tx–Rx frequency space ratio
${r} = \text{0.0245}$
. Also, the proposed structure can cover the entire S-band from
$\text{2}$
to
$\text{4}\;\text{GHz}$
by scaling the sizes of the omega-shaped DGSs to control the resonance frequencies of the embedded BPFs before fabrication. Furthermore, the embedded BPFs have sharp cutoff characteristics, high selectivity, and channel bandwidth of about
${BW} \leq \text{790}\;\text{MHz}$
at
$| {{{s}_{11}}} | = | {{{s}_{22}}} | = - \text{10}\;\text{dB}$
. The simulation and measurement results highly coincide.