A low-profile circularly-polarised (CP) patch antenna with wide axial-ratio (AR) beamwidth is proposed. Based on the transmission-line model, the radiation patterns of a CP patch antenna are calculated by modelling the entire patch as two pairs of equivalent parallel slots. Initially, the mechanism of wide-beamwidth CP radiation pattern is investigated. The results show that the |E_θ| and |E_φ| radiation patterns can be made nearly equalized over a large angular range, if the spacing L between two parallel slots is selected as 0.45 λ₀ (Condition I). For a square patch, the length of each slot must be equal to the spacing L, and it needs to be maintained as one half wavelength at resonance for radiation (Condition II). By using a suspended dielectric substrate, the two above conditions is simultaneously satisfied, resulting to achieve a wide AR beamwidth. After that, the effect of the finite ground size on the 3-dB AR beamwidth is analysed to constitute a practical CP antenna. Finally, the proposed CP antenna is designed and fabricated. Experimental results are in good agreement with the simulated ones in terms of radiation beamwidth, reflection coefficient and AR bandwidth. Practically, the antenna achieves a wide 3-dB AR beamwidth of 120°.