Circular polarised antennas are used in many wireless communication systems where it is necessary to have a wide bandwidth of the return loss and the axial ratio. This paper compares the bandwidth of the above parameters for a circular polarised square patch antenna fed by a two branch coupler and a ring coupler. The design of the two couplers and the patch is initially reviewed. Based on the equivalent circuits of the two couplers and that of the patch the complete antenna is modelled using Microwave Office (AWR) software. The results obtained show that a ring coupler produces a wider bandwidth for the return loss and axial ratio than that obtained by a two branch coupler.
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