A Miniaturised ±45°‐Polarised Co‐Aperture Antenna With High T x /R x Isolation for Wearable Device Applications

ABSTRACT A new miniaturised co‐aperture in‐band full‐duplex antenna with good T x /R x isolation for wearable applications is proposed in this letter. The octagonal patch, which worked as the radiating structure, is minimised by using multiple loading structures, including etching narrow slots distributed circumferentially, loading stubs and rectangular parasites. A pair of cross‐shaped slots and three unequal‐length slots are further loaded near the feeding probes to increase the isolation between ±45° polarisations. For demonstration, a prototype operating at 5.8 GHz is processed. The occupied size is only 0.40λ 0 × 0.20λ 0 × 0.025λ 0 , where λ 0 is the free‐space wavelength at 5.8 GHz. The measured realised gain of each port is more than 0.43 dBi and the T x /R x isolation is better than 25 dB in the bandwidth of 5.75–5.85 GHz.