Omnidirectional Antenna Elements Research Articles

Multiband Dual-Polarized Hybrid Antenna With Complementary Beam for Simultaneous RF Energy Harvesting and WPT

A novel hybrid antenna for simultaneous RF energy harvesting (RF-EH) and dedicated wireless power transfer (WPT) is proposed. The hybrid antenna consists of a multiband dual-polarized omnidirectional antenna element (covering GSM-1800, UMTS-2100, ISM-2400/5800, 5G-3500, and wireless local area network (WLAN) bands) and a 2.4 GHz dual-polarized high-gain directional patch array element. In the WPT band (ISM-2400), directional beams locate at the null of omnidirectional beams, and a pair of spatially complementary beams is obtained. The omnidirectional beams are capable of capturing the ambient RF energy from low-elevation space for low-power circuits, while the directional beams receive the power from a dedicated source to activate high-power modules. Also, the spatially complementary feature contributes low mutual couplings between ports that support the independent operation of WPT and RF-EH. For validation, an outdoor RF-EH test and an indoor WPT test are conducted. The measured results agree with the simulated ones.

Green ultra-wideband antenna utilizing Mie resonances in cactus

While plants are typically supposed to restrict the performance of radio frequency transceiver systems, they can act as efficient biogenic elements of control. A high fraction of water inside vegetation gives rise to multiple electromagnetic Mie resonances, originating from interplaying a naturally high permittivity and a form factor. Opuntia ficus-indica, known as nopal cactus, is a representative example whose succulent stems or cladodes contain nearly 75–85% water. Here, we present an Opuntia-based broadband omnidirectional antenna element, operating at several Wi-Fi communication bands, spanning from 900 MHz to 7.7 GHz. A high relative permittivity in the GHz range exceeds 20. As a result, a variety of Mie resonances within the cladode are measured and revealed by the multipole expansion technique. Modal hierarchy, resonantly excited with a coaxial cable, is demonstrated to provide a broadband impedance matching below −10 dB over the ∼150% bandwidth. Further investigations of plants as functional electromagnetic elements can contribute to the general trend of environment friendly multifunctional devices, promoting development of green technologies.

Integrated epsilon-near-zero antenna for omnidirectional radiation

Antennas with omnidirectional radiation of electromagnetic wave have wide applications in sensing, positioning, and wireless communications. Here, we investigate the potentials of using epsilon-near-zero (ENZ) metamaterial to realize omnidirectional radiation with high degrees of freedom. We propose an omnidirectional antenna based on an ENZ cavity integrated in printed circuits board (PCB). By taking advantage of ENZ behavior, the ENZ antenna can decouple the radiation patterns and the operating frequency while maintaining the omnidirectional radiation characteristic. Based on the omnidirectional ENZ antenna element, a parallel-fed array is realized based on the low-cost PCB process. The integrated ENZ antenna array exhibits the capability of engineering the omnidirectional radiation flexibly, such as beam scanning and beam intensity control for practical applications.

A Tri-Polarized Antenna With Diverse Radiation Characteristics for 5G and V2X Communications

A tri-polarized antenna with diverse radiation characteristics is proposed in this paper. This design mainly consists of two pairs of loop radiating dipoles and an omnidirectional monopole antenna element, which are used for the fifth generation (5G) and vehicle to everything (V2X) communications, respectively. By adding eight pairs of inverted L-shaped patches with unequal sizes around the proposed dipoles, wide beamwidths in both E- and H-planes can be obtained across the desired lower and upper frequency bands. Furthermore, by employing eight fork-shaped microstrip stubs to combine the circular monopole antenna element and the L-shaped patches, the flare angle of the conical beam can be increased to 180°, which results in gain enhancement in the azimuth plane. Finally, the proposed loop radiating dipoles are excited by a pair of symmetrical differentially-fed feeding lines. Consequently, high port isolation for the proposed loop radiating dipoles as well as low gain variations for the monopole antenna element can be achieved. Measured results show that the impedance bandwidths of 32.84% (2.8-3.9 GHz) and 18.18% (4.5-5.4 GHz) can be achieved for the 5G communications. Wide half power beamwidths (HPBW) of larger than 103° in E-plane and 91° in H-plane can be achieved across the operating bands. In addition, a bandwidth of 5.5% (5.82-6.15 GHz) with gain of 2.47 ± 0.69 dBi in the azimuth plane can also be obtained for V2X communications.

AOA Localization for Vehicle-Tracking Systems Using a Dual-Band Sensor Array

The issue of asset tracking in dense environments where the performance of the global positioning system (GPS) becomes unavailable or unreliable is addressed. The proposed solution uses a low-profile array of antenna elements (sensors) mounted on a finite conducting ground. A compact-size sensor array of six electrically small dual-band omnidirectional spiral antenna elements was designed as a front end of a tracker to operate in the 402 and 837 MHz spectrum bands. For the lower band, a three-element superposition method is applied to support estimation of the angle of arrival (AOA), whereas all six sensors are employed for the higher band. A low complexity and accurate AOA determination algorithm is proposed, the projection vector (PV), and this is combined with the array mentioned. Orthogonal frequency division multiplexing (OFDM) is integrated with the PV technique to increase the estimation resolution. The system was found to be suitable for installation on the roof of vehicles to localize the position of assets. The proposed system was tested for the tracking of nonstationary sources, and then two scenarios were investigated using propagation modeling software: outdoor to outdoor and outdoor to indoor. The results confirm that the proposed tracking system works efficiently with a single snapshot.

Wireless Power Transfer Based on Microwaves and Time Reversal for Indoor Environments

Resorting to power accurate delivery for wireless power transfer (WPT) based on microwaves, a theory and method based on time reversal (TR) for WPT in 3D indoor environments are presented in this paper. Conventional WPT methods have the limitations of requiring that the elements on power source array (PSA) must have the same structure and regular arrangement. Unlike those conventional methods, the PSA used in this paper can be constructed by any omnidirectional antenna elements with any structure and any arrangement, whose principles are based on the auto-match of antenna radiation and environment adaptability of TR. Moreover, compared with those conventional methods, which perform complex multi-objective optimizations of beam pattern cost-functions at each frequency for getting excitation of PSA, the proposed algorithm can obtain PSA's excitation over a wide frequency range only by a single run of TR and Fourier transform operations. In addition, by weighting the time reversed charging request signal from powered devices, the interference caused by different observing elevation angles and amplitude difference among each channel can be suppressed effectively. At last, multi-powered devices placed arbitrarily can be charged simultaneously, and get similar power from PSA without power unfairness by our proposed algorithm.

Single-element based ultra-wideband antenna array concepts for wireless high-precision 2-D local positioning

Abstract. We generally categorize the approaches for ultra-wideband antenna array design, and consequently propose simplified concepts for antenna arrays for a high-precision, ultra-wideband FMCW radar 2-D local positioning system to obtain robustness against multi path interference, perform angle of arrival analysis, as well as instantaneous heading estimation. We focus on low-cost and mechanical robust, industrial-application ready antennas. The antenna arrays are optimized for operation in the 5 GHz to 8 GHz frequency range and are designed towards supporting full omnidirectional 360° as well as partial half-plane direction of arrival estimation. Two different concepts for vehicle- as well as wall-mounted antenna array systems are proposed and discussed. We propose a wideband unidirectional bow-tie antenna array element having 97% impedance and 37% pattern bandwidth and a robust vehicle mounted omnidirectional antenna element having more than 85% impedance and pattern bandwidth.

DEVELOPMENT OF A BROADBAND HORIZONTALLY POLARIZED OMNIDIRECTIONAL PLANAR ANTENNA AND ITS ARRAY FOR BASE STATIONS

A novel broadband horizontally polarized (HP) omnidi- rectional planar antenna is developed for mobile communications. The proposed antenna consists of four printed arc dipoles that form a cir- cular loop for HP omnidirectional radiation. A broadband feeding net- work which includes four broadband baluns and an impedance match- ing circuit is designed to excite the four arc dipoles. An eight-element linear antenna array is developed for 2G/3G base stations. A broad- band power divider is used to feed the antenna array. Experimental results show that the HP omnidirectional antenna element has a band- width of 31% (1.66{2.27GHz) while its array has a bandwidth of 34% (1.67{2.35GHz) and an omnidirectional antenna gain of » 8dBi. Both of the antenna element and its array have good omnidirectivity over the 10-dB return loss bandwidth. Simulated and measured results for the antenna element and its array are presented.

A Fast Calculation Method for the Receiving Mutual Impedances of Uniform Circular Arrays

A fast and accurate method is introduced for the determination of the receiving mutual impedances of uniform circular arrays (UCAs) with omnidirectional antenna elements. By using the symmetry consideration for UCAs, the number of unknown receiving mutual impedances is reduced by at least $2(N-1)$ times of that by using a full characterization method. A further improvement of using only a single calibration signal coming from a single incident angle makes the new method much more efficient in facilitating the determination of the receiving mutual impedances of UCAs by either theoretical calculations or by an experimental measurement. Our simulation results and a direction-of-arrival (DOA) estimation example study demonstrate the efficiency and validity of the new method.

Improved mutual coupling compensation in compact antenna arrays

A new method for the characterisation of receiving mutual impedances of compact arrays with omni-directional antenna elements is proposed. Based on a large number of incident waves coming from different directions, the new method is able to calculate the receiving mutual impedances of omni-directional antennas based on a system of equations that characterise the received terminal voltages at different incident wave directions. In the new method, the receiving mutual impedances of all the antenna elements are calculated together in a single equation with the scattering effect from all antenna elements in the array being taken into account. Compared to the previous methods for the characterisation of the receiving mutual impedances, the new method preserves the boundary conditions of the original electromagnetic problem and produces much more accurate results on receiving mutual impedances, especially for compact antenna arrays. Direction finding examples based on the new method demonstrate its superior performance over existing methods.

Effective Mutual Coupling Compensation for Direction-of-Arrival Estimations using a New, Accurate Determination Method for the Receiving Mutual Impedance

Performance degradation due to the mutual coupling effect of antenna arrays in direction-of-arrival (DOA) estimations has been well known, and many mutual coupling compensation methods have been proposed throughout the years. In particular, the mutual coupling effect becomes significant when the antenna elements are closely spaced, which is difficult to compensate. In this paper, a new, accurate method is introduced to determine the receiving mutual impedances of antenna arrays with closely spaced omni-directional antenna elements. This new method uses a number of plane wave sources coming from different directions to determine the receiving mutual impedances of a particular antenna element with all other antenna elements in the array in a single step. This step is repeated for all the antenna elements in the array, and the full mutual impedance matrix of the array is thus obtained. Using the Matrix Pencil Method (MPM), DOA estimations using eight-element arrays were used to demonstrate the validity and accuracy of this new method.

Antenna array optimisation using semidefinite programming for cellular communications from HAPs

Array pattern optimisation based on semidefinite programming is proposed to improve the coverage performance of cellular communications from High Altitude Platforms (HAPs). This optimisation, when applied to a linear vertical array of N omnidirectional antenna elements, allows a coverage performance better than that of an array of N narrowbeam aperture antennas forming hexagonal cells on the ground. In addition to performance enhancement, the HAP antenna payload can be significantly reduced.

Spatial correlation in uniform circular arrays based on a spherical-waves model for mutual coupling

A general framework based on spherical waves is presented for arbitrary oriented antenna elements in a uniform circular array configuration. The technique fully describes all electromagnetic effects in the array by a set of spherical-wave coefficients. This set is limited by the overall electric size of the array. It is demonstrated that the signal correlation between the antenna elements can be calculated directly from these spherical-wave coefficients for certain statistical distributions of the directions of arrival of the incoming signals. The effects of antenna tilt on the signal correlation are investigated. It is shown that because of mutual coupling and pattern non-uniformity, signal correlation can both increase and decrease compared to the case of an ideal array consisting of isotropic and uncoupled antenna elements. Moreover, simulation results show a significant reduction of the mean channel capacity, compared to C max , for uncorrelated antenna signals and omnidirectional antenna elements.

Wideband beamforming using rectangular arrays without phase shifting

Conventional wideband arrays suffer from the implementation of tapped-delay-line processors in the beamforming networks. In this paper, a wideband rectangular array of omni-directional antenna elements is proposed, which requires no phase compensations and employs a single real multiplier for each antenna element. The desired angle and frequency characteristic of the array are the key parameters of the design of the beamformer. Furthermore, the undesired frequency characteristics of the antenna elements can be compensated by the beamformer as well. The most practical advantage of the array is that the number of antenna elements required for a relatively high fractional bandwidth is much lower than other comparable wideband beamformers. Copyright © 2003 AEI.