Design principles of sequentially fed, wide bandwidth, circularly polarised microstrip antennas

The technique of sequentially rotating the feed position of a microstrip patch antenna to improve the circular polarisation bandwidth of an array of such elements is briefly reviewed in the wider context of other known antenna parameter staggering concepts. A first order analysis then shows how the sequential technique significantly improves the axial ratio bandwidth in the relation to the number of patches in the array and the feeder connections. Unwanted effects such as feeder phase errors, multiple reflections in feeders, the presence of higher order modes and mutual coupling are then considered. Computations embracing these effects and measurements illustrate the various properties and topological options available. Finally, the application of the technique is briefly illustrated for a single patch and an array of patches. In conclusion the design principles are summarised and feeder effects are identified as the main limitation when implementing the sequential technique.