Compact dual-band dual-mode circular patch antenna with broadband unidirectional linearly polarised and omnidirectional circularly polarised characteristics

A novel probe-feed single-layer circular patch antenna with dual-band dual-mode dual polarisation is proposed in this study. By using modified mushroom structure, dual-band dual-mode characteristic is realised as former designs. Due to the loading structure including four curved patches added around the circular radiating patch, bandwidth is broadened for the patch mode (n = 1 mode) with unidirectional linearly polarised characteristics at the upper frequency band. By loading with four curved branches in the ground plane, circularly polarised property for the dipole mode (n = 0 mode) with omnidirectional radiation patterns is achieved at the lower frequency band. Parameter analysis is made to study this antenna and one prototype is fabricated to confirm the property. Moreover, the measured results are obtained with −10 dB impedance bandwidths of 227.5 MHz (5.1% at the centre frequency of 4.42 GHz) and 857.5 MHz (14.9% at the centre frequency of 5.74 GHz), and maximum gain of 1.1 and 7.1 dB for the dipole mode and patch mode, respectively. With the advantages of simple structure, wide bandwidth, radiation pattern selectivity and polarisation diversity, this antenna concept is valuable in wireless communications.