A low-profile microstrip patch antenna (MPA) with wide bandwidth, wide beamwidth, and reduced cross-polarisation is proposed here. Firstly, the far-zone radiated fields of the MPA are deeply studied to improve its radiation performance. It demonstrates that the E-plane half-power beamwidth (HPBW) of the antenna could be progressively widened by using a single equivalent slot instead of two equivalent slots. Meanwhile, its high cross-polarisation of the H-plane radiation patterns could be successfully decreased down by enlarging the width of the rectangular patch and loading the shorting pins. Secondly, the input impedance of the MPA operating in the fundamental mode is extensively investigated. The results illustrate that the resonant frequencies of its dual modes could be reallocated in proximity to each other for bandwidth enhancement by properly selecting the dimension of radiating patches. Finally, the proposed antenna is fabricated and tested. Experimental results show that the antenna has gained an improved bandwidth (|S|<-10 dB) of about 12% ranging from 2.70 to 3.03 GHz, while keeping a thin thickness of about 0.029 free-space wavelength. Besides, its H-plane cross-polarisation is kept below -20 dB. Most importantly, the E-plane HPBW of the antenna is extended to around 140° over the wide band.