Compact dual concentric ring printed antennas

A novel small printed antenna structure is prepared that, depending on the excitation orientation, can yield low crosspolarised field generation or good quality circular polarisation (CP). The configuration consists of concentric shorted annular ring printed antennas. Each ring is loaded by a localised dielectric layer and can therefore be optimised to operate at a certain frequency, thereby enhancing the overall bandwidth of the antenna. Probe-fed configurations are investigated such that the appropriate feed network can be located below the radiating elements, thus minimising the footprint of the entire antenna. For a balanced feed configuration, the overall size of the antenna (including the ground plane and feed network) was 5×7×1.3 cm for operation centred at 2.1 GHz. The 10 dB return loss bandwidth was approximately 11.5% and the crosspolarisation levels were more than 15 dB below the co-polar patterns for both principle planes. The CP version was of similar size with an impedance bandwidth of 12.4% and a 3 dB axial ratio bandwidth of 16%.