A low profile, high gain, CPW-fed, slot antenna is proposed for CubeSats. The proposed antenna is backed with a low profile metallic reflector. The cavity reflector is utilized to significantly improve gain and reduce back lobe radiation. The antenna has a compact size of 36×36 mm 2 , meaning it is compatible with any CubeSats standard structure. We have simulated the antenna on a 2U CubeSat (10cm×10cm×20cm). Our results show that the antenna achieves good impedance matching with a return loss of-30 dB at the desired frequency of 2.45 GHz, a-10-dB impedance bandwidth of 109 MHz (2.391-2.50 GHz) and has a total gain of 8.62 dB.