Abstract: In this paper, Ka-band rectenna (rectifying antenna) is analyzed with harmonicwave balance method (HBM).Power conversion efficiency of the rectenna is caculated.Low-pass filter and dc-pass filter of rectenna are optimized with regarding conversion efficiency as object function.A new rectenna is obtained which has 60% power conversion efficiency from microwave to do under 150 mW input power and 100Ω load resistance.At same time the rectenna is modeled by time domain method (TDM).Agreement is achieved betueen results of HBM and those of TDM,which shows the effective-ness of theoretical results.The computational results show that the power conversion efficiency of rectenna is influenced greatly by touch (serises) resistance and zerobias junction capacity of diode.