Study on ellipticity properties of single-feed-type circularly polarised microstrip antennas

The letter presents the basic method for the design of single-feed-type circularly polarised microstrip antennas (SCPA). An SCPA designed to operate under condition of circular polarisation (OCCP) proved to produce an axial ratio below 0.5 dB at the boresight. Moreover, the measured and calculated axial ratios for SCPA agreed well within the effective range. These results indicate the use of the design method reported in the letter for construction of SCPA with excellent directivity.