Dipole Elements Research Articles

A novel uniplanar wideband magneto-electric dipole antenna element

A novel uniplanar wideband magneto-electric dipole antenna element is proposed in this paper. The proposed antenna is composed of the conventional bow-tie radiation patch as an electric dipole, a semi-circular loop, which works as a magnetic dipole, a coplanar ground plane, two directors with different lengths for enhancing gain, and a microstrip-to-coplanar stripline transition balun. The designed antenna adopts a small-size coplanar ground plane to achieve a uniplanar structure. Consequently, this method reduces the space size immensely and makes the antenna suitable for the array application. In addition, a tapered slot structure is utilized to improve impedance matching. The prototype of the proposed antenna was fabricated and measured. The measured results keep in good accordance with the simulated ones. The simulated results show that the proposed antenna obtains a broad impedance bandwidth of 60.5% from 2.25 to 4.20 GHz (voltage standing wave ratio [VSWR] ≤ 2) which can be applied for wireless local area network (WLAN) (2.4–2.484 GHz), worldwide interoperability for microwave access (WiMAX) (2.5–2.69/3.4–3.69 GHz), and long term evolution (LTE) (2.5–2.69 GHz). Meanwhile, the stable gain, low cross-polarization, stable unidirectional radiation patterns, and low back lobe are obtained within the operating frequency band. The array composed of the proposed antenna elements is also investigated in this paper.

Investigations of a Load-Bearing Composite Electrically Small Egyptian Axe Dipole Antenna

An electrically small, metamaterial-inspired Egyptian axe dipole (EAD) antenna has been investigated for use in structural composite materials. The EAD antenna consists of a differentially fed dipole element integrated with a near-field resonant parasitic EAD element. These elements have been adapted to these materials resulting in a system that is impedance matched and radiates efficiently at 307 MHz. Three cases have been identified and investigated to ascertain the performance of the manufacturing techniques and material properties used to build these electrically small antennas, as well as their performance characteristics. Uniquely, an embroidered conductive thread and a new carbon fiber based, nonwoven mat have been investigated for use as the conducting elements. Both cases are compared with a copper variant of the EAD antenna. All three prototypes were tested. Measurements confirm that both the nonwoven mat and the embroidered versions of the EAD antennas perform similarly with maximum realized gains ranging from 1.72 to 1.90 dBi.

The Path to a Transportable Ionospheric Heater—Tuning Methods

A tunable electrically small antenna (ESA) designed to be naturally resonant at 100 MHz is evaluated for its range of tuning and feasibility for use in a mobile ionospheric heating (MIH) setup. The overarching goal is to match the ionospheric heating performance of the 180 element array at the high frequency active auroral research program (HAARP), which occupies approximately $1.2 \times 10^{5}~\text{m}^{2}$ of land in Gakona, Alaska. While each HAARP crossed dipole element occupies 440 $\text{m}^{2}$ of land and is tunable in the range of 2.7–10 MHz using automatic matching networks, the presented ESA approach is aimed toward enabling the fabrication of a transportable MIH array platform capable of high continuous wave (cw) power, albeit with a linear dimension five to ten times smaller than that of an equivalent dipole antenna. It is elucidated that the capacitively tuned ESA is continuously tunable to a frequency about 50% lower than that of the ESA’s base frequency, albeit the resonant antenna structure carries a fractional bandwidth of merely 1%–2%.

3-wave mixing Josephson dipole element

Parametric conversion and amplification based on three-wave mixing are powerful primitives for efficient quantum operations. For superconducting qubits, such operations can be realized with a quadrupole Josephson junction element, the Josephson Ring Modulator, which behaves as a loss-less three-wave mixer. However, combining multiple quadrupole elements is a difficult task so it would be advantageous to have a three-wave dipole element that could be tessellated for increased power handling and/or information throughput. Here, we present a dipole circuit element with third-order nonlinearity, which implements three-wave mixing. Experimental results for a non-degenerate amplifier based on the proposed third-order nonlinearity are reported.

Near-Field Shielding Performances of EMI Noise Suppression Absorbers

This paper describes a systematic study on the near-field behavior of an electromagnetic interference (EMI) noise suppression absorber materials considering two different types of commercial absorbers and different types of excitation source: at first, elementary electric dipole and elementary magnetic loop, and then using real dimensions of a coaxial cable for designing a dipole and loop. Virtual versions of the material are created and simulated with the purpose of understanding the mechanisms of high values of power loss when the absorber is in the near field of the source The focus of this study is the evaluation of the electromagnetic power balance in near field for each absorbing material and considered source to understand their near-field shielding properties. Full-wave simulations and measurement are performed and compared to verify the performance of the EMI noise suppression absorber materials in the near field.

Wideband circularly polarised antenna based on tightly coupling effect

A new design of a circularly polarised antenna based on the tightly coupled mechanism is presented. The proposed antenna consists of four tightly coupled dipoles, four impedance transforming networks and a wideband feeding network. Owing to the strong mutual coupling between coupled dipole elements, the proposed antenna realises a wide operating bandwidth. A prototype is manufactured and measured to validate the method. The measured results indicate that the proposed design provides a 10 dB return loss bandwidth of 101% (1.7-5.2 GHz) and a 3 dB axial ratio bandwidth of 77% (2.0-4.5 GHz). The design has a 3 dB gain bandwidth of 56% from 2.6 to 4.6 GHz with a peak gain of 10.4 dBic. Acceptable agreements can be obtained between the simulated and measured results.

Null Placement in Time-Modulated Linear Antenna Arrays of Dipole Element

ABSTRACTThis paper describes the practical implementation of time-modulated linear dipole antenna arrays (TMLDAAs) using EM simulator. Cat swarm optimization (CSO) algorithm is applied to improve the null performance of TMLDAAs by radio frequency switch. The nulls at the particular positions of the direction of arrival of a TMLDAA can be reduced effectively by the proper optimization of current excitation weights and an effective design of switch-on time intervals of each element. CSO gives the optimized value of the current excitation weights of the radiation pattern. The optimized results obtained by CSO algorithm using MATLAB simulation are practically implemented and are designed through computer simulation technology–microwave studio simulation software for half-wave dipole antenna arrays. The dipole antenna is designed to operate at a resonant frequency of 2 GHz. The antenna exhibits a frequency band from 1.8331 to 2.1285 GHz, which is applicable for wireless applications.

High-Power Photodiode-Integrated-Connected Array Antenna

We present a novel optical feeding technique to achieve efficient excitation of an ultrawideband-connected array (CA) antenna. The passive fiber optic feed allows for preservation of the theoretical bandwidth and low profile of elementary connected dipole elements. In order to improve effective radiated power, high-power charge compensated modified unitravelling carrier photodiodes are integrated into an antenna array for the first time. Circuit and full-wave simulations, which include all required antenna and feed components, are conducted for the optimization of the array's performance. A 9 × 12 element CA is populated with a 1-D array of four photodiode-integrated active elements to demonstrate the concept. The optically fed array is confirmed experimentally to have a 3-dB bandwidth of approximately 7–17 GHz, in good agreement with simulations.

An optimal LAA subsystem designed using Gravitational Search Algorithm

A Linear Array Antenna (LAA), a subsystem of a Wireless Communication System (WCS), with 12 number of dipole elements are optimally designed using Gravitational Search Algorithm (GSA). GSA being one of the suitable optimisation algorithms, used to optimise many design parameters of this subsystem to get a number of desired performance parameters using a simple weighted sum type multi-objective function. The LAA subsystem is designed here, mainly to realise high directivity, high front-to-maximum-side-lobe-level, and low half power beam width for WCS application at ultra high frequency. The LAA designed using GSA is also validated using MININEC for transparency. The successful optimal design approaches, application, and comparative study of this system with an un-optimised system presented here can also be extended to other antennas.

Analysis and Design of Transmitarray Antennas

In recent years, transmitarray antennas have attracted growing interest with many antenna researchers. Transmitarrays combines both optical and antenna array theory, leading to a low profile design with high gain, high radiation efficiency, and versatile radiation performance for many wireless communication systems. In this book, comprehensive analysis, new methodologies, and novel designs of transmitarray antennas are presented. Detailed analysis for the design of planar space-fed array antennas is presented. The basics of aperture field distribution and the analysis of the array elements are described. The radiation performances (directivity and gain) are discussed using array theory approach, and the impacts of element phase errors are demonstrated. The performance of transmitarray design using multilayer frequency selective surfaces (M-FSS) approach is carefully studied, and the transmission phase limit which are generally independent from the selection of a specific element shape is revealed. The maximum transmission phase range is determined based on the number of layers, substrate permittivity, and the separations between layers. In order to reduce the transmitarray design complexity and cost, three different methods have been investigated. As a result, one design is performed using quad-layer cross-slot elements with no dielectric material and another using triple-layer spiral dipole elements. Both designs were fabricated and tested at X-Band for deep space communications. Furthermore, the radiation pattern characteristics were studied under different feed polarization conditions and oblique angles of incident field from the feed. New design methodologies are proposed to improve the bandwidth of transmitarray antennas through the control of the transmission phase range of the elements. These design techniques are validated through the fabrication and testing of two quad-layer transmitarray antennas at Ku-band. A single-feed quad-beam transmitarray antenna with 50 degrees elevation separation between the beams is investigated, designed, fabricated, and tested at Ku-band. In summary, various challenges in the analysis and design of transmitarray antennas are addressed in this book. New methodologies to improve the bandwidth of transmitarray antennas have been demonstrated. Several prototypes have been fabricated and tested, demonstrating the desirable features and potential new applications of transmitarray antennas.

Probe gain via four-wave mixing based on spontaneously generated coherence**Project supported by the Natural Science Foundation of Hainan Province, China (Grant Nos. 20151005, 20151015, and 20161006), the National Natural Science Foundation of China (Grant Nos. 11247005, 51262007, 11501153, and 41564006), the Postdoctoral Scientific Research Program of Jilin Province, China (Grant No. RB201330), the Project Sponsored by Science Research Foundation for

We have studied the probe gain via a double-Λ atomic system with a pair of closely lying lower levels in the presence of two probe and two coherent pump fields. The inversionless gain can be realized by using nondegenerate four-wave mixing under the condition of spontaneously generated coherence (SGC) owing to near-degenerate lower levels. Note that by using SGC, two probe fields can be amplified with more remarkable amplitudes, and the gain spectra of an extremely narrow linewidth can be obtained. Last but not least, our results show that the probe gain is quite sensitive to relative phases due to the SGC presence which allows one to modulate the gain spectra periodically by phase modulation, and can also be influenced by all laser field intensities and frequencies, and the angles between dipole elements.

Broadband Dipole-Loop Combined Nanoantenna Fed by Two-Wire Optical Transmission Line

This paper presents a broadband nanoantenna fed by a two-wire optical transmission line (OTL). The antenna is defined by a combination of a dipole and a loop, where only the dipole element is connected to the OTL. The analysis is fulfilled by the linear method of moments with equivalent surface impedance to model the conductors. Firstly, the nanoantenna alone is investigated, where the input impedance, current distribution, reflection coefficient, fractional bandwidth, radiation efficiency, and radiation pattern are analyzed. Then, the input impedance matching of this antenna with the OTL is considered. In this case the current, near field distribution, radiation pattern, and reflection coefficient are calculated for different geometrical parameters. The results show that the loop inserted in the circuit can increase the bandwidth up to 42% and decreases the reflection coefficient in the OTL to −25 dB.

Design of Novel Broadband Endfire Dipole Array Antennas

A novel broadband endfire dipole array antenna is presented in this letter. With a novel impedance matching method, this antenna is realized as a series-fed structure and four dipole elements on the same printed circuit board. The bandwidth of the antenna is increased by staggered tuning of the dipole elements. The measured results show that the antenna has an impedance bandwidth of 70.5% for voltage standing wave ratio ( $\mathrm{VSWR)} , a gain of 3.43–6.78 dBi and endfire radiation pattern. The total size is $0.595\times 0.977\; \lambda _o^2$ ( $\lambda _o$ is the free-space wavelength at the center frequency). The studies of the dipole length and distributed capacitor are also performed to verify the design theory. The advantages of broad bandwidth and unidirectional radiation pattern make this antenna favorable in wireless communication systems.

Design of a Compact Log-Periodic Dipole Array Using T-Shaped Top Loadings

A compact log-periodic dipole array (LPDA) is presented with size-reduced dipole elements. With T-shaped top loading, the length of individual dipole elements is reduced by 45% compared to that of λ/2-dipole elements. The compact LPDA is simulated and fabricated for measurement verification. The measured 10-dB impedance bandwidth is 87.3%, and the average realized gain in the direction of the shortest dipole is 5.1 dBi over the operating bandwidth.

Bandwidth Enhancement of a Horizontally Polarized Omnidirectional Antenna by Adding Parasitic Strips

A horizontally polarized omnidirectional antenna with enhanced impedance bandwidth is presented in this letter. The proposed antenna consists of a feeding network, four printed dipole elements with etched slots, parasitic strips, and director elements. Four identically curved and printed dipole elements are placed in a square array and fed by a feeding network with uniform magnitude and phase; thus, the proposed antenna can achieve an omnidirectional radiation. To enhance the impedance bandwidth, parasitic strips and etched slots are introduced to produce additional lower and upper resonant frequencies, respectively. By utilizing four director elements, the gain variation in the horizontal plane can be improved, especially for the upper frequency band. With the structure, a reduced size of 0.63 λ L × 0.63 λ L × 0.01 λ L ( λ L is the free-space wavelength at the lowest frequency) is obtained. The proposed antenna is designed and fabricated. Measurement results reveal that the proposed antenna can provide an impedance bandwidth of 84.2% (1.58-3.88 GHz). Additionally, the gain variation in the horizontal plane is less than 1.5 dB over the frequency band 1.58-3.50 GHz, and increased to 2.2 dB at 3.80 GHz. Within the impedance bandwidth, the cross-polarization level is less than -23 dB in the horizontal plane.

A Longitudinally Compact Yagi–Uda Antenna With a Parasitic Interdigital Strip

A Yagi–Uda antenna with a parasitic interdigital strip is proposed for a compact design. The parasitic strip is positioned between a driven dipole element and a reflecting element to compensate for the phase change, while high gain and good impedance matching is achieved for the proposed antenna with significant longitudinal reduction. The experimental results show that the proposed two-element Yagi–Uda antenna realizes a gain of 5.1 dBi with the spacing of only 0.06λ0, compared to the conventional spacing of 0.21λ0 (λ0 is the guided wavelength at 1.48 GHz). The overall size of the proposed antenna is 0.57 λ 0 × 0.12 λ0.

FOCUSING THE VERTICAL ELECTRIC DIPOLE RADIATION BY THE PENDRY LENS

The flat lens conception was considered in the pioneering work of V.G. Veselago, who considered the possibility of electromagnetic waves propagation in media with simultaneously negative permittivity and permeability (according to modern terminology − in the left-handed metamaterials). Later, J.B. Pendry put forward the idea of the so-called "superlens", the resolution of which would exceed the diffraction limit. In view of the prospects for the practical applications it has caused a discussion on the possibility of anti-parallelism of phase and group velocities and the actual super-resolution implementation for the source in the form of a monopole. However, using the ray theory approximation reduced the generality of the results, neglecting losses radically distorted them, and errors in the theoretical analysis led to the wrong physical interpretation. In this paper, we obtained a rigorous solution to the problem of focusing radiation from elementary electric dipole located perpendicularly to the plane layer of finite thickness made of the left-handed metamaterial with absorption. Spatial distribution of the electromagnetic field in the layer, as well as the incident and reflected fields at various heights of the dipole, layer thickness and losses in each medium are numerically simulated. The analysis of the calculated spatial structure of the electromagnetic field confirmed the focusing ability of the interfaces between ordinary and left-handed media, as well as a flat lens.

Low-Profile Compact Dual-Band Unit Cell for Polarizing Surfaces Operating in Orthogonal Polarizations

This communication introduces a novel periodic reflector which provides linear to circular polarization (CP) conversion in two frequency bands. Significantly, the reflector converts a slant 45° linearly polarized wave into two orthogonal CPs over two separate frequency bands while further the unit cell dimensions are maintained below the critical grating lobe limit of half wavelength. Unlike previous designs providing this performance, which are based on linear dipole elements, miniaturization is here achieved by exploiting resonances in both TE and TM polarized waves. The operating principle of the polarizer is discussed and a parametric study is presented to derive design guidelines. A prototype working in the satellite Ku-band has been designed and tested to validate the proposed design. The proposed polarizer can find applications in multiple-beam satellite antenna systems in order to reduce the number of reflector apertures in a single-feed-per-beam configuration.

Synthesis of linear aperiodic array using Cauchy mutated cat swarm optimization

A novel Cauchy mutated cat swarm optimization (CMCSO) that features effective global search capabilities with fast convergence is introduced in this paper. The Cauchy mutation enables the cats of the cat swarm optimization (CSO) algorithm to seek their positions in directions that avoid the problem of premature convergence and local optima. In this communication, CMCSO is applied to the synthesis of linear aperiodic arrays for minimizing sidelobe level and controlling the null positions. Various synthesis examples are considered and the obtained results are compared with linear aperiodic array designs from literature. Numerical results demonstrate that the proposed method is superior to existing methods in terms of accuracy and convergence speed. Some of the synthesized aperiodic array designs are implemented with wire dipole antenna elements using a full-wave electromagnetic simulator. Furthermore, experiments are conducted on several standard benchmark complex multimodal problems to demonstrate the effectiveness of the proposed method. The sensitivity analysis is performed on different parameters of CMCSO to demonstrate their influence on the overall performance of the benchmark and antenna array synthesis problems.

Polarimetric Radar Barcode: A Novel Chipless RFID Concept With High Data Capacity and Ultimate Tag Robustness

This paper presents a novel chipless radio frequency identification (RFID) concept where the information is encoded on the tag with a 2-D polarimetric radar barcode. We achieved a data capacity with this technique that is outstanding for chipless RFID. Even though these chipless RFID tags are simple, they are extremely robust in harsh environments. The polarimetric radar barcode is formed by a set of geometric structures like small dihedral mirrors, plane surface elements, or dipole elements with different polarimetric backscattering behaviors. These structures are arranged in a 2-D array to create a specific polarimetric 2-D radar barcode. The information is read by polarimetric millimeter-wave imaging radar. The lateral resolution of the radar determines the minimum resolvable element size and is therefore critical for the maximum data capacity of the tag. We show that, theoretically, a data capacity of more than 800 bit on a surface less than the size of a credit card can be achieved if a millimeter-wave multiple-input multiple-output radar is used as reader. The polarimetric encoded reflectors can be formed by metal or reflecting ceramic structures, and the tag can consist of a single material. Thus, tag robustness is limited only by the robustness and temperature resistance of the material used. We verify the performance and functionality of the proposed chipless RFID concept with measurements taken in a laboratory test setup with a 20-bit tag and a millimeter-wave radar system with 77.5-GHz center frequency.