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A single-layer integrated microstrip array antenna for dual circular polarisation is proposed. It consists of an orthogonal linearly polarised microstrip array antenna and a 90° hybrid circuit using a single-layer substrate. The orthogonally polarised array antenna uses double-sided microwave-integrated circuit (MIC) technology including airbridges, effectively. It has excellent isolation and cross-polarisation suppression performance between the orthogonal modes and flexibility of the antenna size extension. By integrating it with the 90° hybrid circuit, the proposed array antenna can excite the orthogonal circular polarisations [right-hand circular polarisation (RHCP), left-hand circular polarisation (LHCP)] simultaneously. It is possible to easily realise wireless integration modules because of a single-layer structure. The simulated and experimental results show good circular polarisation performance for both the RHCP and LHCP. The design frequency is 10°GHz and the 3°dB axial ratio bandwidths of both the RHCP and LHCP are approximately 10° in the experiment.