Monopole Array Research Articles

Array Surface-Wave Launcher for the Efficient Generation of Shaped Beam and Multibeam With Metasurface

A new architecture is provided for the efficient generation of shaped beams and multiple shaped beams (in amplitude, phase, and polarization), with leaky-wave (LW) metasurfaces (MTSs). Those antennas are usually fed by a surface-wave (SW) launcher, which evenly illuminates the MTS versus azimuth, through a cylindrical SW. When the interest lies in generating pencil beams or particular types of shaped beams, the required radiating aperture field (linked to the Fourier transform of the desired radiation pattern) on the MTS is almost azimuthally symmetric in amplitude. However, for a wide class of shaped beams, the desired aperture field is far from being azimuthally symmetric. This leads to an MTS design in which some sectors exhibit a very small surface impedance modulation. Those sectors tend to leave the SW intact until it reaches the rim of the surface, where the power is either reflected or diffracted at the slab rim. We solve this efficiency problem by reducing the amount of power fed into some sectors, through the use of an array of feeding monopoles. The azimuthal illumination of the feeder should be designed to match the azimuthal asymmetry of the desired aperture field. The corresponding MTS surface impedance is then determined using a method of moments (MoM)-based synthesis technique. Several examples are provided to illustrate the concept. The improvement in terms of antenna efficiency is numerically demonstrated.

Evaluation of 8-Channel Radiative Antenna Arrays for Human Head Imaging at 10.5 Tesla.

For human head magnetic resonance imaging at 10.5 tesla (T), we built an 8-channel transceiver dipole antenna array and evaluated the influence of coaxial feed cables. The influence of coaxial feed cables was evaluated in simulation and compared against a physically constructed array in terms of transmit magnetic field (B1+) and specific absorption rate (SAR) efficiency. A substantial drop (23.1% in simulation and 20.7% in experiment) in B1+ efficiency was observed with a tight coaxial feed cable setup. For the investigation of the feed location, the center-fed dipole antenna array was compared to two 8-channel end-fed arrays: monopole and sleeve antenna arrays. The simulation results with a phantom indicate that these arrays achieved ~24% higher SAR efficiency compared to the dipole antenna array. For a human head model, we observed 30.8% lower SAR efficiency with the 8-channel monopole antenna array compared to the phantom. Importantly, our simulation with the human model indicates that the sleeve antenna arrays can achieve 23.8% and 21% higher SAR efficiency compared to the dipole and monopole antenna arrays, respectively. Finally, we obtained high-resolution human cadaver images at 10.5 T with the 8-channel sleeve antenna array.

Optimization of the Measurement Technique for Emissions in Reverberation Chamber Using the Equivalence Principle

This paper presents an optimization of a method to reconstruct the radiated emissions of an equipment under test by the measurement of the electric field samples collected on the walls of a reverberation chamber. This means that only the orthogonal component of the electric field is necessary to obtain the radiative behavior of the device in free space conditions. The use of the equivalence principle allows one to reduce the number of equivalent sources used to reconstruct the radiation of the device. In fact, in the previous version of the method, the sources are placed into the entirety of working volume of the reverberation chamber. In the current version of the method, only the surface surrounding the equipment under test is discretized. The analytical implementation of the method is proposed for a particular stirring action: the multiple monopole source stirring technique. This technique is based on an array of monopoles placed onto the walls of the cavity, and therefore no further hardware is needed for the reconstruction of the radiated emissions. The method is experimentally validated in a real scenario.

A Novel Ultrawideband Gear-Shaped Dielectric Ring Resonator Antenna

In this study, a novel ultrawideband (UWB) dielectric ring resonator (DRR) antenna has been proposed. DRR antennas include a single monopole antenna in the center of a ground plane and a dielectric with a symmetric structure around the monopole. This structure will lead to ultrawide band antenna. However, it is still possible to enhance the antenna bandwidth. In this study, we combine the DRR structure with an array antenna. The proposed antenna includes a circular array of four triangle resonators, which is rotated around the center of the triangle base to form a gear-shaped ring resonator antenna. In this design, characteristics of all these antennas are combined to enhance the antenna bandwidth including triangular dielectric resonator, circular array antenna, dielectric ring resonator structure, and a quarter-wave electric monopole. Triangular dielectric resonator antennas are wideband and in small size. Ring resonator antennas are inherently ultrawideband. Quarter-wave electric monopole and circular array structure can also enhance antenna bandwidth. This novel shape of the DRR antenna possesses the wider impedance bandwidth compared to similar works. Impedance bandwidth is 150% (5.2–36.1 GHz), and the bandwidth ratio is 1 : 6.9, which is much greater than earlier reports.

Advanced monopole and dipole sonic log data processing — Part 1: Real time

Real-time open-hole wireline sonic logging data processing becomes a nontrivial task to accurately, automatically, and efficiently evaluate the compressional and shear slowness of a borehole rock formation when human interaction is not possible and the signal processing time is limited to the elapsed time between different transmitter excitations. To address real-time sonic data processing challenges, we have developed self-adaptive, data-driven methods to accurately measure the formation P- and S-wave slowness from monopole and dipole waveforms in all types of formations. These new real-time processing techniques take advantage of the fact that advanced wireline sonic logging tools have wide frequency responses and little to no detectable tool body arrivals. These technology improvements provide an opportunity to implement a first-motion-detection technique that detects the onset of P-waves in the monopole array waveforms. The knowledge of compressional arrival time and corresponding slowness are then used to project an appropriate slowness-time window to identify the monopole refracted S-wave and its slowness based on the range of possible compressional to shear velocity ratio ([Formula: see text]/[Formula: see text]) for earth rock formation. To process the borehole dipole flexural waves, we develop a new, data-driven frequency-domain method that enables the evaluation of the full flexural-wave dispersion response and its corresponding low-frequency shear slowness asymptote. Field data processing results indicate that our methods provide high-quality compressional slowness (delta-T compressional) and shear slowness measurements that are not affected by other borehole modes or dispersion complications in most formation types.

Hedgehog-lattice spin texture in classical Heisenberg antiferromagnets on the breathing pyrochlore lattice

The hedgehog lattice, a three-dimensional periodic array of magnetic monopoles and antimonopoles, is known to be realized in the presence of the Dzyaloshinskii-Moriya (DM) interaction. Here, we demonstrate by means of Monte Carlo simulations that the hedgehog lattice is induced by not the DM interaction but frustration in classical Heisenberg antiferromagnets on the breathing pyrochlore lattice. In the model, the breathing bond-alternation is characterized by the ratio of the nearest-neighbor (NN) antiferromagnetic exchange interaction for large tetrahedra to that for small ones, J1'/J1. A quadruple-q state with the ordering vector of q=(\pm 1/2,\pm 1/2,\pm 1/2), which is realized for a large third NN antiferromagnetic interaction along the bond direction J3, turns out to become the hedgehog-lattice state in the breathing case of J1'/J1 <1, while in the uniform case of J1'/J1 =1, it is a collinear state favored by thermal fluctuations. It is also found that in a magnetic field, the structure of the (1/2,1/2,1/2) hedgehog lattice is changed from cubic to tetragonal, resulting in a nonzero net spin chirality which in a metalic system, should yield a characteristic topological Hall effect.

Low-Cost and High-Gain Microstrip Magnetic Dipole Antenna With All-Metal Structure and Open-Ended Stubs

A novel microstrip magnetic dipole antenna is proposed in this work with an all-metal structure and open-ended stubs. The antenna is designed with an all-metal structure to improve bandwidth and gain. Open-ended stubs are used to replace the shorting walls of a microstrip magnetic dipole antenna for convenient fabrication. Furthermore, the open-ended stubs produce additional radiation and enhance the antenna gain. Our analysis shows that each stub can be regarded as a monopole element and the proposed antenna can be regarded as a combination of a monopole array and a microstrip magnetic dipole antenna. The proposed antenna produces broadside radiation with a peak gain of 13.1 dBi and a bandwidth from 2.38 to 2.51 GHz. The antenna can be easily manufactured because it is built entirely by metal, with no shorting structure. It is promising to provide long-distance transmission for 2.4 GHz WLAN applications.

A Novel Dual-Band Decoupling Technique

This article presents a novel dual-band decoupling network (DN) to increase the isolation between two antennas. It is composed of two dual-band Wilkinson power dividers, four additional transmission lines (TLs), and two reactive components. The decoupling formulas are derived from systematic design procedures. Hence, the design parameters of the power divider, lengths of TLs, and reactances of reactive components can be precisely determined to realize high port isolation. Two benchmarks of the two-element symmetric and asymmetric monopole arrays are used to elaborate the design procedure and demonstrate the advantages of proposed DN. Results show that the proposed DN can offer good impedance matching, high port isolation, high efficiency, and low envelop correlation coefficient (ECC) at both designated frequencies, which verified the proposed decoupling concept and theory.

Antenna-Array Network Model

An antenna can be modeled as a two-port network using S-parameters. However, having individual antenna S-parameters is not sufficient for modeling an array of antennas as antennas exhibit mutual coupling. This article proposes a network model to represent an antenna array with mutual coupling. Using the proposed model, an $N$ -element antenna array is modeled as a combination of two-port networks representing each element and an $N$ -port network representing mutual coupling. Two techniques to calculate mutual coupling S-parameters are presented: a primary method using numerical solutions and an approximate method using approximate expressions. The proposed model was validated using four monopole arrays having different interelement spacings, the number of elements, and nonidentical antennas.

A Lightweight Planar Ultrawideband UHF Monopole Mills Cross Array for Ice Sounding

An electrically large ultrawideband ultrahigh frequency (UHF) monopole antenna array has been designed to sound up to 3 km of ice and meet the logistical requirements of transportation to arctic regions. The monopole array is comprised of 16 planar subarray modules, which in combination form a 16 m by 17 m Mills cross array configuration to maximize sensitivity and spatial selectivity in both cross-track and along-track directions. Each planar subarray module is 1 m by 2 m in size with a 6.35 cm thick rigid insulation foam panel separating the individual monopole elements from metal foil ground plane on the top such that the maximum radiation is directed to nadir. Each subarray panel consists of 4 by 8 circular monopole antenna elements with a spacing of 0.25 m. Each monopole element is printed on a 130 mm by 80 mm 62 mil FR4 board. The total weight of each subarray panel is 9 kg, making for very lightweight and low-profile antenna construction. The antenna array together with the radar system was deployed to the East Greenland Ice-coring Project site in August 2018 for demonstrating surface-based ice sounding at the UHF band.

Magnetic hedgehog lattices in noncentrosymmetric metals

The magnetic hedgehog lattice (HL) is a noncoplanar magnetic texture with a periodic array of magnetic monopoles and anti-monopoles. Despite phenomenological and numerical studies thus far, there remain open issues on the microscopic origin, especially with respect to the recent experimental findings of two different types of HLs even at zero magnetic field. Here, we study the stability of the HLs for an effective spin model with long-range interactions arising from itinerant nature of electrons. By variational calculations and simulated annealing, we find that the HLs are stabilized in the ground state at zero magnetic field by the synergetic effect of the anti-symmetric exchange interactions generated by the spin-orbit coupling and the multiple-spin interactions generated by the spin-charge coupling. We also clarify the phase diagram in the magnetic fields, which includes topological phase transitions with pair annihilation of the monopoles and anti-monopoles depending on the field directions.

Novel Wideband Microstrip Monopole Antenna Designs for WiFi/LTE/WiMax Devices

In this paper, two compact and broadband microstrip monopole antennas have been proposed, designed, and presented using two novel sets of design equations. Each monopole antenna design has different dimension and characteristic. The proposed designs have been verified using a commercial electromagnetic simulator (CST-Studio) and implemented prototypes mounted on FR-4 substrate having a thickness of 1.6 mm. In addition, a linear array consists of only two monopole elements has been designed and presented to enhance the gain of the proposed monopole antenna. Simulation results confirmed the validity of the two novel sets of design equations for both monopole and array antennas. Also, the proposed array antenna (38 × 36 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> size), achieved a moderate gain of (6.0 dBi), a satisfying efficiency of (81%), a VSWR that is less than 1.2 and a 22% fractional bandwidth of about 1200 MHz. Moreover, simulated and measured return losses of the proposed monopole antennas (single and array) accomplish a reasonable agreement. The proposed monopole antennas are simple designs and compact in size, and they can be used for many wireless applications including WiFi, LTE, and WiMax. In addition, a compact array of large monopole number can achieve a higher gain that is up to 18 dBi (four to eight monopole array elements with overall size 38 × 72 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to 38 × 144 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). The novelty of this paper is by introducing the proposed and closed form design equations for a monopole introducing the length of monopole and ground of substrate dimensions as a function of ϵ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> and thickness.

Decoupling and Cloaking of Interleaved Phased Antenna Arrays Using Elliptical Metasurfaces

We apply the concept of electromagnetic invisibility/cloaking to improve the radiation properties and decouple two tightly spaced and interleaved phased linear antenna arrays of strip monopoles operating at close frequencies, in order to restore their isolated radiation patterns and eliminate the undesired cross-coupling between their elements. We realize this effect using elliptically shaped cloaking metasurfaces designed for mutually cross-coupled elements of the distinct arrays. We analyze and investigate the cloaking and decoupling effects in improving the functionality of the coupled arrays in terms of their radiation patterns and realized gain, respectively. As a result, the antenna arrays placed in close proximity of each other can radiate independently for a wide range of beam scanning angles, restoring the properties they would have when isolated from each other.

Design and analysis of radio antenna monopole arrays in the military world

The analysis and design of the proposed antennas is designated for receiving voice signals from Radio in general are out-of-prominent antennas and smaller indoor antennas, in this research, the authors aim to design and analyse an antenna with a simple design, a small dimension efficient, very easy installation, cheap and meet the antenna characteristics to support the movement in combat training within the Army. The antenna to be discussed is a monopole antenna Arrays with a minimalist shape that works at frequencies between 350MHz - 480MHz by adjusting the length of the horizontal elemental Active distance between the outer and inner to get the impedance matching. In order to obtain a unidirectional pattern, a metallic plane reflector is placed at a distance of about λ/4 from the array board: predicted gain (11 dB for 5 × 1 array and 15 dB for 9 × 1 array) and bandwidth (around 600 MHz) are larger than for conventional micro strip patch arrays having similar board dimensions. the proposed antenna has been numerically analysed for wireless communication systems.

Novel Reliable and Practical Decoupling Mechanism for Strongly Coupled Antenna Arrays

In this paper, a novel antenna decoupling approach is investigated. The introduced concept is based on expelling the currents flowing between the closely spaced antennas through a tapered slot etched on the array ground plane. The method is free from extra-reactive components and transmission lines. Although they are closely spaced and strongly coupled, the technique allows a high improvement in port isolation. A practical implementation of this mechanism is applied to a monopole array of two elements working at 2.45 GHz and closely packed ( $0.069\lambda _{0}$ ). The obtained results are very attractive, and a decoupling of about 40 dB is achieved with good impedance matching. Moreover, radiation diversity is obtained with a gain of 1.9 dBi. Furthermore, the decoupled array is integrated in a real receiving system, and the proposed decoupling technique is checked through the array signal processing. Hence, the obtained results confirm the effectiveness of the proposed decoupling mechanism. In addition to its efficient port isolation, the most attractive features of the proposed decoupling technique are simplicity and ease of implementation in compact multiantenna devices.

Adjoint-based optimization of sound reinforcement including non-uniform flow.

The determination of optimal geometric arrangements and electronic drives of loudspeaker arrays in sound reinforcement applications is an ill-posed inverse problem. This paper introduces an innovative method to determine complex driving functions, also considering complex environmental conditions. As an alternative to common frequency domain methods, the authors present an adjoint-based approach in the time domain: Acoustic sources are optimized in order to generate a given target sound field. Instead of the Helmholtz equation, the full non-linear Euler equations are considered. This enables an easier treatment of non-uniform flow and boundary conditions. As proof of concept, a circular and a linear monopole array are examined. For the latter, the environmental conditions include wind and thermal stratification. For all examples, the method is able to provide appropriate driving functions.

Laboratory and in situ sound absorption measurement under a synthetized diffuse acoustic field

This article reports numerical and experimental results concerning the estimation of the diffuse field sound absorption coefficient of several different materials under a synthetized diffuse acoustic field excitation in laboratory and in situ conditions. The proposed measurement method is based on a sound field reproduction approach and a synthetic array of acoustic monopoles facing the material to be tested. Numerical simulations are first conducted to optimize the geometrical parameters of the method and to compute theoretical sound absorption coefficients of the considered materials. Measurements on a set of six typical acoustic materials are then conducted following the standardized reverberant room method as well as the proposed approach in a hemi-anechoic room and in two realistic rooms. Albeit showing limitations in the low-frequency domain, the proposed method enables a significant reduction of the tested specimen dimensions compared with the reverberant room method and allows performing tests in non-ideal acoustic environments.

Developing a Direction-Finding System and Channel Sounder Using a Pseudo-Doppler Antenna Array [Education Corner

This article reports the development of a direction-finding (DF) system and channel sounder, at 5.8 GHz, by a team of undergraduate and graduate students from the University of Alabama, Tuscaloosa, for the 2018 IEEE Antennas and Propagation Society (AP-S) Student Design Contest. Based on the competition's transmitter (Tx) specifications, a link budget was calculated to determine the components of a receiving-antenna system. Accordingly, a low-cost, small, battery-powered software-defined radio (SDR) based on a pseudo-Doppler antenna array (PDAA) receiving system was constructed using a HackRF One (HO) SDR, an Opera Cake (OC) switching board, and a circular array of omnidirectional monopoles (the PDAA). For digital signal processing, GNU Radio software was used.

Novel and Efficient Parasitic Decoupling Network for Closely Coupled Antennas

A novel and efficient parasitic decoupling network (PDN) is proposed for closely coupled antennas in this paper, which provides a new perspective and approach to design DNs based on the parasitic decoupling concept. The PDN is composed of sections of transmission lines (TLs) and reactive components, allowing additional power-traveling paths. With the TL lengths and reactive-component reactances being precisely determined, the traveling power from one antenna to another could cancel out the undesired power wave induced by mutual coupling, resulting in the high port isolation. The decoupling theory is rigorously derived with the design procedure of the PDN systematically described in connection with two examples of the two- and three-element monopole arrays. The measurement results show that good impedance matching for each antenna port, isolations of more than 25 dB, total efficiencies of more than 64%, and envelop correlation coefficients (ECCs) of less than 0.07 are attained simultaneously for both examples using the proposed PDN. The results verified the decoupling theory and proved the PDN concept.

Interactions between vortical, acoustic and thermal components during hypersonic transition

Discrete unstable modes of hypersonic laminar boundary layers, obtained from an eigenvalue analysis, provide insight into key transition scenarios. The character of such modes near the leading edge is often identified with the corresponding asymptotic free-stream behaviour of acoustic, vortical or entropic (thermal) content, which we designate fluid-thermodynamic (FT) components. In downstream regions, however, this direct one-to-one correspondence between discrete modes and FT components does not hold, since FT components interact in well-defined ways with the basic state and with each other (even under linear scenarios). In the present work, we perform an FT decomposition of discrete modes using momentum potential theory, to yield a physics-based analysis that complements linear stability theory in the linear regime, and seamlessly extends to the nonlinear domain where direct numerical simulations are appropriate. Linear and nonlinear saturated disturbance effects, different forcing types and wall thermal conditions are considered, with emphasis on phenomena occurring near stability-mode synchronization locations. The results show that, in the linear regime, each discrete mode contains all FT components, whose relative amplitudes vary with streamwise distance. Vortical components are always the largest, followed by thermal and acoustic components. These latter two show distinct fore and aft signatures near mode synchronization. The vortical component displays a series of rope-shaped recirculation-cell patterns across the generalized inflection point. However, both acoustic and thermal components display ‘trapped’ structures. The former contains an alternating monopole array between the wall and the critical layer, while the latter is confined to an undulating region between the wall and a wavy locus straddling the generalized inflection point. Nonlinear saturation in the region of Mack-mode growth further strengthens the rope-shaped structures in the vortical component and higher harmonics appear, whose form and location depend on the specific component. Wall cooling modifies the eigenfunctions such that the acoustic component accounts for more of its composition, consistent with its destabilization. Analysis of energy interactions among the FT components indicates that, even though the vorticity component is the largest, the thermal component induces the most significant source term for the growth of acoustic perturbations, possibly due to the trapped nature of both.