Microwave power transmission using rectenna technology has attracted a strong interest in conjunction with wireless electric power delivery to infrastructure and subjects located at a remote place. A typical rectenna, which is a major component of the wireless power transmission technology, consists of an antenna, a Schottky diode, and low-pass filters for low-frequency electromagnetic wave isolation in the device. To obtain high efficiency, an electromagnetic wave is collected through a high-resonance antenna, and the AC mode of coupled wave energy is delivered to a Schottky diode that rectifies AC power into DC power. By connecting rectennas in series or parallel, or in mixed way — as well as enlarging the receiving area — the rectenna array can capture microwave energy into a desirable mode of high power.

This invention introduces a new design for high-frequency operation beyond V-band. The new design includes parallel plate-type shunt capacitors and via connection on a double-layer layout. It is based on previous work on rectenna development for X-band operation using a dipole antenna structure. In a typical rectenna design, the rectenna consists of a dipole antenna, a low-pass filter, a Schottky diode, and a shunt output capacitor.

Placing two capacitors on both ends of the rectenna structure is important to suppress the re-radiation of high-order harmonic waves. In this invention, the direct connection between the dipole antenna and the shunt capacitor is removed, and two parallel plate capacitors replace the planar capacitors in a typical design. The parallel plate shunt capacitors with high-capacitance values can isolate high-order harmonics within the rectenna structure, and suppress re-radiation of the second and third harmonics through the antenna. Moreover, additional transmitted wave loss at the fundamental frequency can also be eliminated in this design. The capacitance ratio between planar and parallel plate capacitors on the same projected area is more than 20 times, which is directly related to the blocking efficiency comparison of the new and old designs.

Another key feature in this design is the DC routing with via structure connecting the top layer and the bottom layers through the substrate material. DC electrical potential at the top layer is transferred to the bottom layers with negligible loss through vias. An electrical signal with the same polarity from each rectenna is connected in parallel, and the electrical current from individual rectennas can be summed up and increase output power.

The design avoids the direct connection and replaces the function with shunt capacitors and parallel connection of the DC line at the opposite side of a dielectric film using via connection. Using this concept, resonance frequency of the dipole antenna can maintain a low level of return loss even under the variation of impedance values of the adjacent device features. Isolation of faulty diodes can be obtained by removing the lines and blocking the electromagnetic wave propagation at the shunt capacitor. In addition, the benefit of a small cross-section area by a two-layer layout can increase the effective area for power conversion and overall efficiency of a rectenna array.

This invention will provide robust operation during the high power conversion, and upgrade power conversion efficiency of a rectenna wireless power transmission technology. Potential impacts of this application can extend to consumer electronics, industry, military, medical, and transportation.

This work was done by Hargsoon Yoon, Sang H. Choi, Kunik Lee, and Kyo D. Song of Langley Research Center. NASA is seeking partners to further develop this technology through joint cooperative research and development. For more information about this technology and to explore opportunities, please contact This email address is being protected from spambots. You need JavaScript enabled to view it.. LAR-18135-1

NASA Tech Briefs Magazine

This article first appeared in the June, 2016 issue of NASA Tech Briefs Magazine.

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