Capacitive probe-fed compact dual-band dual-mode dual-polarisation microstrip antenna with broadened bandwidth

One novel dual-band dual-mode dual-polarisation microstrip antenna with broad bandwidth is designed and analysed in this study. In the lower frequency band, the antenna operates in the dipole mode with linearly polarised omnidirectional radiation pattern, whereas in the upper frequency band, the antenna works in the patch mode with circularly polarised directional radiation patterns. The bandwidth of the patch mode is broadened by adding curved parasitical patches around the centre radiating patch which is fed by the capacitive probe. Parameter analysis is made to further explore the working principle and one prototype is realised for verification. Moreover, the measured results show that the -10 dB impedance bandwidths for the dipole mode and patch mode are 227.5 MHz (4.8% at the centre frequency of 4.72 GHz) and 1330 MHz (23% at the centre frequency of 5.78 GHz), respectively, among which the 3 dB axial ratio bandwidth of the patch mode is 510 MHz (8.8% at the centre frequency of 5.815 GHz). Moreover, the maximum gains of the two modes are 1.1 and 8.4 dB, respectively. This single-feed patch antenna is valuable in future applications for its compact structure, considerable bandwidth, radiation pattern and polarisation diversity.