Compact printed ultra-wideband diversity monopole antenna with slant inverted tree-shaped stub

A compact two-port diversity antenna is proposed and experimentally investigated. One of the ports is connected to a microstrip feed, whereas the other port to a coplanar waveguide feed. The radiating elements are semi-circular disc-shaped monopoles rotated around their centres. By shaping the common ground plane, ultra-wide impedance bandwidth is achieved. The measured bandwidths are 2-12 GHz at port 1 and 2.3-10.2 GHz at port 2. To obtain good isolation between the ports, a slant inverted tree-shaped structure is attached at the corner of the ground plane. The measured isolation is about 20 dB throughout the band. The antenna has omni-directional radiation patterns with a moderate peak gain of 2-7 dBi. To evaluate the diversity performance, the envelope correlation coefficient, diversity gain and capacity loss are calculated. A modified design with impedance bandwidth at port 2 extending beyond 11 GHz is also presented. The proposed diversity antenna is an attractive candidate to provide polarisation diversity and enhance channel capacity in a rich scattering environment.