Abstract: An S-band wideband circular reflector aperture array was designed used for spatial power combining based on solid state microwave source, the reflector element employed a novel back-fired helix antenna as the feeder, so that to avoid the aperture blockage by fed line or the sub-reflector. The helix feed was tapered to obtained wider bandwidth, 38% percent band width was obtained after optimization of the geo-parameters, then the reflector element and the aperture array were simulated and design, the results were that frequency band is from 2.3 GHz to 3.4 GHz, the gain in the band is greater than 31.5 dB, and the axial ratio is lower then 3 dB.