A wideband dual-circularly polarised (CP) substrate integrated waveguide (SIW) cavity-backed patch antenna is designed by using twolayer structure. The realised dual-CP, a cavity-backed square patch lies on the top substrate is excited by two pins, which are symmetrically located at an offset to the diagonal axis of the patch. These pins induce strong loading effect in the cavity and generate additional resonances in the vicinity of the patch resonant that help to achieve a wideband response by adjusting their locations. Thus, generation of dual-CP and wide impedance bandwidth is accomplished by using this new feeding topology. Moreover, the antenna is fabricated and tested for dual-CP. The experimental results show an impedance bandwidth of nearly 28.4% (8.59-11.43 GHz) and an axial-ratio bandwidth of 3.4% under the criterion <3-dB. © 2017 The Institution of Engineering and Technology.