This letter presents a high-efficiency 2.45-GHz rectenna that can harvest low input RF power effectively. A new antenna with a simple structure and high gain of 8.6 dBi is proposed for the rectenna. The antenna is designed to directly match the rectifying circuit at 2.45 GHz and mismatch it at the second and third harmonics so that the use of bandpass filter between the antenna and rectifying circuit can be eliminated. The rectenna shows a maximum conversion efficiency of 83% with a load resistance of 1400 Ω. Furthermore, the overall conversion efficiency can remain 50% for the low, -17.2 dBm (corresponding power density 0.22 μW/cm2 ) input power level.

Design of a High-Efficiency 2.45-GHz Rectenna for Low-Input-Power Energy Harvesting

Microwave power transmission (MPT) is the wireless transfer of large amounts of power at microwave frequencies from one location to another. MPT research has been driven primarily by the desire to remotely power unmanned aerial vehicles (UAVs) and by the concept of space solar power (SSP) first conceived by Dr. Peter Glaser of the Arthur D. Little Company in 1968. This paper attempts to reveal, in adequate chronological detail, many of the MPT milestones reached over the past 50 years, including those related to SSP. Key components to various MPT systems are presented as well as design schemes for achieving efficient MPT. Special focus is given to rectenna design since this particular MPT component has received the most attention from researchers over the last couple of decades.

Microwave Power Transmission: Historical Milestones and System Components

This paper reports a new circularly polarized rectenna whose rectifying circuit includes two diodes. The rectenna consists of a coplanar stripline (CPS) truncated patch antenna and CPS bandpass filter, which can block harmonic signals up to the third order reradiating from the rectifying circuit. The rectenna is printed on Rogers Duroid 5880 substrate with /spl epsiv//sub r/=2.2 and a thickness of 20 mil. The new dual-diode rectenna can provide at least twice the dc output voltage than the traditional rectenna with only a single diode, which has the same layout dimension as the single-diode rectenna. The dual-diode rectenna achieves an RF-to-dc conversion efficiency of 76% at 5.8 GHz. The proposed rectennas can be interconnected to form the rectenna arrays by series, parallel, and cascaded connections. It is found that a cascade connected rectenna array can provide the highest output voltage. The antenna element can be easily extended to become a traveling-wave antenna or array suitable for high output voltage or current in wireless power transmission applications.

5.8-GHz circularly polarized dual-diode rectenna and rectenna array for microwave power transmission

A novel six-band dual circular polarization (CP) rectenna for ambient radio frequency (RF) energy harvesting is presented. Due to the nonlinearity and complex input impedance of the rectifying circuit, the design of a multiband and/or broadband rectenna is always challenging and its performance can be easily affected by variation in the input power level and load. Therefore, an improved impedance matching technique is introduced, which is aimed to improve the performance of the rectifier with a varying condition. A broadband dual CP receiving antenna is proposed, which has a very wide bandwidth (from 550 to 2.5 GHz) and a compact size. An annular ring structure and a novel feeding technique are employed in order to reduce the size and improve the antenna performance. As a result, the proposed rectenna is the first design that covers six frequency bands, including part of the digital TV and most cellular mobile and WLAN bands in the U.K., while the optimal load range for a constant conversion efficiency is from 10 to 75 $\text{k}\Omega $ . The measured results show that the maximum harvested dc power of the rectenna in typical outdoor and indoor environments are 26 and 8 $\mu \text{W}$ , respectively; it can therefore be applied to a range of low-power wireless applications.

A Novel Six-Band Dual CP Rectenna Using Improved Impedance Matching Technique for Ambient RF Energy Harvesting

The reflectarray has significant promise in applications requiring high-gain, low-profile reflectors. Recent advances in tuning technology have raised the possibility of realizing electronically tunable reflectarrays, which can dynamically adjust their radiation patterns. This paper presents an electronically tunable reflectarray based on elements tuned using varactor diodes. Modeling approaches based on an equivalent circuit representation and computational electromagnetics simulations are presented. Both techniques accurately predict the scattering characteristics of the unit cell as compared to experimental measurements. The development of a unit cell with over 320omicron of phase agility at 5.5 GHz is discussed. Finally, a 70-element electronically tunable reflectarray prototype operating at 5.8 GHz is presented. Radiation pattern measurements with the reflectarray demonstrate its dynamic beam-forming characteristics. Measurements of the gain of the reflectarray correlate well with theoretical expectations.

Modeling and Design of Electronically Tunable Reflectarrays

This paper reports a 0.5-m-diameter right-hand circularly polarized planar reflecting antenna array that uses 437 printed microstrip ring elements of variable rotations to achieve cophasal far-field radiation and wide-band performance at a focal length of 0.35 m. The array is etched on Rogers Duroid 5870 substrate with /spl epsiv//sub r/= 2.33 and 0.508-mm thickness. At 7.1 GHz, the reflectarray achieves an efficiency of 41.7% with a gain at broadside of 27.6 dB. Sidelobe suppression is greater than 17.3 dB, and the left-hand cross-polarization is 23.2 dB below the desired right-hand component. The best efficiency of 45.7% and the maximum gain of 28.2 dB occur at 7.3 GHz.

Circularly polarized reflectarray with microstrip ring elements having variable rotation angles

This paper reports a new circularly polarized (CP) high-gain, high-efficiency rectifying antenna (rectenna) array designed in a coplanar stripline (CPS) circuit. The array can maintain a constant dc output voltage regardless of its broadside orientation. The array is etched on Rogers Duroid 5870 substrate with /spl epsiv//sub r/=2.33 and 10 mil thickness. High-gain dual rhombic loop antennas and a reflecting plane are used in order to reduce the total number of rectenna elements necessary to cover a fixed area. Each antenna has a CP antenna gain of 11 dB and a better than 1 dB axial ratio fractional bandwidth of 4.7%. The single element rectenna achieves 81% RF-to-dc coversion efficiency at 5.71 GHz and uses a CPS band-reject filter (BRF) to suppress the reradiated harmonics by more than 19 dB. At 5.61 GHz, using an array loading of 150 /spl Omega/, a 3 /spl times/ 3 rectenna array produces 0.86 W of dc output power with an RF-to-dc conversion efficiency of 78% and an axial ratio of 0.25 dB for an incident CP power density of 7.6 mW/cm/sup 2/.

B. Strassner

Papers

Circularly polarized reflectarray with microstrip ring elements having variable rotation angles

Highly efficient C-band circularly polarized rectifying antenna array for wireless microwave power transmission