This thesis lays out the design procedure for a left-hand circularly polarized, high-efficiency rectifying antenna on a flexible substrate for use at 10 GHz. The rectenna system is designed for space based power applications. The rectenna employs a dual rhombic loop antenna to achieve circular polarization with an axial ratio of less than 2 dB. The design is milled on a 100 micron thick DuPont Pyralux TK substrate with ϵr=2.5. A lowpass filter is integrated into the coplanar stripline transmission line to suppress the re-radiated harmonics generated by the rectifier circuit. An RF-to-DC conversion efficiency of 58% is achieved. To the author’s knowledge, this is the first rectenna designed on a fully flexible substrate at X-Band.