Bandwidth enhanced dual-band patch-coupling microstrip antenna with omnidirectional CP and unidirectional CP characteristics

Patch-coupling method is adopted to broaden the bandwidth of one dual-band dual-mode dual-circular polarisation (DBDMDCP) circular microstrip antenna in this paper. The function of dual-band dual-mode (DBDM) is excited by simplified metamaterial structure. Curved branches loaded on the ground plane and slots perturbation of radiating patches are used to excite the circular polarisation (CP) property for both n=0 omnidirectional mode and n=1 mode unidirectional mode, respectively. By loading four parasitical coplanar coupling patches on the top surface, the impedance of the patch mode is obviously broadened. Furthermore, methods of coplanar coupling and cascade coupling with circular patches are both adopted to broaden the axial ratio (AR) bandwidth maintaining the impedance matching condition. Considering the processing precision, the cascade coupling type is finally fabricated and compared with the probe-fed type for verification. Measurement results show that impedance bandwidths of 4% (centered at 4.52GHz) and 17% (centered at 5.89GHz) with maximum gain of 1.0dBic and 7.1dBic are realised for the dipole mode and patch mode, respectively. Furthermore, the 3dB axial ratio (AR) bandwidth of the patch mode is 9.2% (520MHz centered at 5.66GHz). Compared with the former designs, this one owns simpler structure, considerable bandwidth besides of pattern and polarisation diversity.