Reconfigurable slot-coupled microstrip antenna with polarisation diversity

The design of an aperture-coupled microstrip patch antenna whose radiation can be switched between circular polarisation (CP) and linear polarisation (LP) states is presented. For the proposed design, the CP and LP radiations are excited through the couplings of a ring slot and an open-ring slot in the ground plane, respectively. The effects of the key parameters of the proposed design on the CP and LP performances are investigated in details. A prototype that uses a pin diode to reconfigure the coupling slot is implemented and tested. From the obtained results, the prototype has a cross polarisation level of more than 25 dB when it is operated at the LP state and an axial ratio of less than 3 dB when it is operated at the CP state. Moreover, the two states share a 10 dB input impedance bandwidth. Consequently, the proposed reconfigurable microstrip antenna has the feature of polarisation diversity at a fixed frequency band