Single-feed circularly polarised aperture-coupled square ring slot microstrip antenna

A novel single-feed circularly polarised aperture-coupled square patch is presented, where a square ring slot has been adopted to implement the coupling mechanism. By introducing some simple modifications of the square ring and patch geometries (namely a couple of meanders and slots), a 3 dB axial ratio fractional bandwidth of up to 9 is achieved. Explicit reference is made to the design of a WiMax antenna operating in the 3.3 - 3.8 GHz frequency band. The antenna has been fabricated and characterised.