Joseph A. Hagerty

Recycling ambient microwave energy with broad-band rectenna arrays

This paper presents a study of reception and rectification of broad-band statistically time-varying low-power-density microwave radiation. The applications are in wireless powering of industrial sensors and recycling of ambient RF energy. A 64-element dual-circularly-polarized spiral rectenna array is designed and characterized over a frequency range of 2-18 GHz with single-tone and multitone incident waves. The integrated design of the antenna and rectifier, using a combination of full-wave electromagnetic field analysis and harmonic balance nonlinear circuit analysis, eliminates matching and filtering circuits, allowing for a compact element design. The rectified dc power and efficiency is characterized as a function of dc load and dc circuit topology, RF frequency, polarization, and incidence angle for power densities between 10/sup -5/-10/sup -1/ mW/cm/sup 2/. In addition, the increase in rectenna efficiency for multitone input waves is presented.

An experimental and theoretical characterization of a broadband arbitrarily-polarized rectenna array

Planar rectenna arrays for rectification of broadband electromagnetic waves of arbitrary polarization are designed and characterized. The performance of the arrays is accurately predicted using a combination of full-wave analysis for the passive part of the rectenna and harmonic balance simulations for the nonlinear rectification process. The arrays used in this paper to demonstrate the principles of operation consist of self-similar right-hand and left-hand polarized spirals which are simulated and measured over a 2.5:1 band (6-15 GHz). Two arrays with different diodes exhibit conversion efficiencies from 5 to 45% under monochromatic linearly polarized illumination with power densities from 1-1.6 mW/cm/sup 2/.

Scalable RF Energy Harvesting

This paper discusses harvesting of low-power density incident plane waves for electronic devices in environments where it is difficult or impossible to change batteries and where the exact locations of the energy sources are not known. As the incident power densities vary over time and space, distributed arrays of antennas with optimized power-management circuits are introduced to increase harvested power and efficiency. Scaling in array size, power, dc load, frequency, and gain is discussed through three example arrays: a dual industrial-scientific-medical band Yagi-Uda array with a low-power startup circuit; a narrowband 1.96-GHz dual-polarized patch rectenna array with a reconfigurable dc output network designed for harvesting base-station power; and a broadband dual-polarized 2-18-GHz array with multi-tone performance. The efficiency of rectification and power management is investigated for incident power densities in the 1-100-μW/cm2 range.

Broadband Rectenna Arrays for Randomly Polarized Incident Waves

This paper presents a new approach to efficient rectenna arrays for arbitrarily polarized incident waves with broad spectral content. The approach is validated experimentally on a dense grid array that rectifies two orthogonal linear polarizations, and on a self-similar spiral array with alternating right-hand and left-hand circular polarizations. The two arrays operate from 4.5to 8GHz and 8.5to 15GHz and have maximum open circuit voltages of 3.5 and 4.0 V, respectively. Their efficiencies increase above 35% and 45%, respectively, for higher incident powers.

A 10 GHz integrated class-E oscillating annular ring element for high-efficiency transmitting arrays

An X-band oscillating element can be achieved in compact form with class-E operation and high directivity. An annular ring is used both as the radiating element and microstrip feedback circuit for the class-E amplifier. A maximum conversion efficiency of the DC power consumption to radiated copolarized power is 55% at 10 GHz with maximum effective radiated power of 23.6 dBm and total radiated power of 15.5 dBm. This active antenna element is shown to be a good candidate for high aperture efficiency spatial power combining.

A 10 GHz active annular ring antenna

An X-band oscillating element can be achieved in compact form with high-efficiency operation and high isotropic conversion gain. An annular ring is used here both as the radiating element and microstrip feedback circuit for the amplifier. A maximum DC-RF conversion efficiency for co-polarized radiated power is 55% at 10 GHz with maximum effective radiated power of 23.6 dBm and total radiated power of 15.5 dBm. The active ring is a good candidate for high aperture efficiency spatial power combining arrays and compact low-cost wireless sensors.

Front-End Processing with Lens Antenna Arrays for Direction-of-Arrival Estimation

Spectral estimation and direction-of-arrival (DOA) estimation is considered for discrete lens antenna array front ends. In this approach, when using the Multiple Signal Classification (MUSIC) algorithm, the dimension is reduced by the front end which performs spatial processing, resulting in increased computational speed and decreased computational load. As a specific example, simulations of a 33-element lens array with DOA estimation for 7 simultaneous sources shows that the computational load is reduced to 68% of that for a 33-element linear uniform array. In this paper, we consider the case of narrowband uncorrelated signals, and uniform spacing of receivers on the lens image surface, but the analysis can be extended to broadband non-uniform scenarios.

Passive Millimeter-Wave Ranging Using Discrete Lenses with Wave-Front Coding

This paper presents an approach to millimeter-wave passive ranging using a method that has been demonstrated in the visible range. Ranging is achieved for multiple objects by way of a receiving discrete lens with modulated amplitude and/or phase response. The result is a set of image patterns with orthogonally coded, range dependent spatial frequency content. We present simulations on a relatively small (100-element) discrete lens antenna array with a cosinusoidal amplitude mask and half-wavelength period at 94 GHz. The feasibility of the approach along with comparisons to the optical counterpart are discussed.