For energy-harvesting devices, the rectifying antenna (rectenna) is crucial. A broadband rectenna that uses a printed monopole antenna and bandpass stub bandpass filter has been developed by Tae-Ui Hong, Kyoung-Min Oh, Hyun-Wook Lee, Hee Nam, and Tae-Soon Yun from Seoul's Kwangwoon University together with Dae-Sung Lee, Hak-In Hwang, and Jong-Chul Lee from the Korea Electronics Technology Institute. This antenna was designed at 2.45 GHz for the wireless transmission of microwave power.
Because the rectifying circuit with a stub filter is fabricated on the groundplane, it does not increase the size of the antenna. That groundplane is widened to acquire the broadband characteristic of the monopole antenna. Using a 270-O load resistor, the rectenna can obtain RF-to-DC conversion efficiency of 66 percent. From 2 to 3 GHz, conversion efficiency above 50 percent is maintained. See "Novel Broadband Rectenna Using Printed Monopole Antenna And Harmonic-Suppressed Stub Filter," Microwave And Optical Technology Letters, May 2010, p. 1194.