Energy is a valuable resource that can be harvested from many different sources, including from wireless radio signals. Armed with an efficient rectenna, which is a combination of an antenna and a rectifying circuit, an electronic device can literally extract dc power from the air, so as to power an electronic device and/or recharge its batteries.

As part of the recent International Microwave Symposium (IMS) student design competition for wireless energy harvesting, students were invited to share their design efforts on developing rectennas for use at different wireless frequency bands. Valentina Palazzi of the University of Perugia and Massimo Del Prete and Marco Fantuzzi of the University of Bologna, both in Italy, rose to the challenge . They developed a broadband rectenna with 25% bandwidth centered at 800 MHz (700 to 900 MHz).

The student engineers experimented with the mechanical configuration of the antenna design, choosing a planar antenna with a tapered slot for broad impedance bandwidth and low losses. With the aid of CST Studio Suite electromagnetic (EM) simulation software, the students were able to simulate and optimize the performance of the planar antenna design to achieve a fractional bandwidth of 22.3%.

The planar antenna, with dimensions of 130 × 140 × 0.254 mm3, provides maximum gain of 3.6 dBi across the operating bandwidth with input power levels of –10 to 0 dBm. Maximum efficiency is 65%. To complete the rectenna, a number of different commercial diodes were considered for the rectifier circuit design. Once diodes were selected, matching circuits were developed for an efficient connection to the antenna, and multiple measurements were made to confirm that prototype performance was fairly close to computer-simulated performance.

See “Scavenging for Energy,” IEEE Microwave Magazine, Vol. 18, No. 1, January/February 2017, p. 91.