A dual-frequency dual-circularly polarised patch antenna with wide beamwidth is proposed. The two-layer structure comprises circular patches with offset circular slots connected to rectangular slots. They provide orthogonal perturbations realising RHCP and LHCP for the lower and upper bands, respectively. The wide beamwidth is realised by extending the substrate beyond the groundplane. Measurements show a maximum beamwidth of 180° and gains of 3.9 and 0.5 dBic for zenith and 10° elevation, respectively, for the upper band. The measured beamwidth for the low band is 130° with a maximum gain of 3.9 and -0.7 dBic for zenith and 10° elevation, respectively. The axial-ratio is less than 3 dB in the hemisphere for elevations greater than 10° for both bands.
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