Low-profile circularly polarised patch-ring antenna with compact feeding network

This study presents a low-profile circularly polarised microstrip antenna with two radiators composed of a cornertruncated patch and a corner-truncated ring. They are stacked and printed on the two sides of a suspended FR4 substrate. The axial ratio (AR) bandwidth of the proposed design is greatly improved compared with the traditional patch by merging the existing bandwidth of the patch with the additional bandwidth of the ring. Parametric analysis indicates that the modes of the patch and the ring can be tuned independently. A λ/4 microstrip line is meandered in the inner part of the ring to reduce the size of the feeding network. The antenna profile is only 0.065λ. A prototype of the proposed antenna is built and tested. The simulated and measured results agree well. The measured 10 dB return-loss bandwidth is 20.6% (2.375-2.88 GHz) and the 3 dB AR bandwidth is 6.94% (2.39-2.56 GHz). The measured gain is ~7 dBiC in the concerned bandwidth, with a variation of 1 dB.