Coupled Dipole Research Articles

A Dual Slant-Polarized Cylindrical Array of Tightly Coupled Dipole Antennas

This study proposes a design of a low-profile ultra wide-band cylindrical antenna array with plus/minus 45-degree dual polarization. The proposed compact cylindrical antenna array produces an omnidirectional radiation pattern in the azimuth plane to cover all directions. It consists of <inline-formula> <tex-math notation="LaTeX">$20\times 4$ </tex-math></inline-formula> dual-polarized elements within a diameter of 131 mm and a height of 116 mm. The array elements are tightly coupled slant-polarized wideband dipole antennas, and hence, rotational symmetry of radiation patterns in the horizontal plane is achieved for the two orthogonal polarizations. Furthermore, a metasurface structure has been designed and placed over the interconnected array elements to achieve ultrawideband capabilities. The proposed array provides less than &#x2212;10 dB reflection coefficient over a frequency band between 1.7 GHz and 5.9 GHz. The cross-polarization discrimination (XPD) is 15 dB at boresight in the azimuth plane. The electromagnetic characteristics of the cylindrical array and its corresponding planar array before bending have been evaluated and compared via simulations, and verified by measurements. The compact size, lightweight, and printable design of the proposed antenna array enable low-cost manufacturing and ease of installation. The proposed array design overcomes many challenges encountered in wide-band MIMO systems by covering the entire sub-6 GHz band while providing wide 360-degree coverage in the azimuth plane, hence, supporting multibeam applications.

Packable and Readily Deployable Tightly Coupled Dipole Array (TCDA) With Integrated Planar Balun

To overcome the limited payload dedicated to onboard antennas for CubeSat/SmallSat applications, this paper presents a novel, foldable, dual-polarized Tightly Coupled Dipole Array (TCDA). In comparison to previous vertical feeds used for TCDAs, this array integrates a planar microstrip balun feed to enable foldability. The proposed array attains 5.4:1 (0.6-3.20 GHz) impedance bandwidth with VSWR < 3 at broadside and scans down to 45∘ at all azimuth planes. Notably, a substrate-integrated in-plane folding mechanism based on Lamina Emergent Torsion (LET) joints is employed to achieve foldability coupled with a simple fabrication process. The average simulated radiation efficiency was 95% across the band. A 5 × 8 prototype array was fabricated and tested to verify the finite array’s foldability, bandwidth, and gain performance. This prototype achieves 80% one-dimensional size reduction, yielding 60% overall volume reduction. Consequently, the array prototype can be folded and stowed in a compact volume of 1.4U ( 25 cm× 7.2 cm× 9 cm ).

A Novel Reflection-Type Polarization Convertor Design Using Connected Orthogonal Tightly Coupled Dipole Arrays

Herein, we design a polarization convertor (PC) using two orthogonally polarized, tightly coupled dipole arrays (TCDAs) connected in cascade, of which one is used for the reception of incident waves and the other is used for their transmission. The operation of the PC is elucidated via a cascading equivalent circuit of unit cells of orthogonally polarized TCDAs. The critical role of vertical metal strips (VMSs) with regard to wide-angle insensitivity is discussed. Moreover, it is found that the undesirable common mode occurs under oblique incidence and its frequency is related to the size-to-height ratio of the unit cell. To demonstrate the performance of the proposed PC, a 40 × 40 array structure is fabricated and measured using the Naval Research Laboratory (NRL) arch method. The simulated bandwidth range is 2.06 to 14.54 GHz (7.06:1) for a polarization conversion ratio (PCR) ≥ 80%, and the measured bandwidth range is 1.68 to 14.51 GHz (8.64:1) for a PCR ≥ 72% at an incident angle of 10°. At an incident angle of 40°, the simulated and measured bandwidths are 2.15 to 14.13 GHz (6.57:1) and 2.43 to 13.87 GHz (5.71:1) for a PCR ≥ 80%, respectively.

A Wideband and Wide Scanning Tightly Coupled Dipole Array with Meta-Surface Wide-Angle Impedance Matching

A low profile ultra-wideband tightly coupled dipole array is studied. The antenna elements are fed by Marchand baluns of small size and low cost. A metasurface based wide-angle impedance matching (MSWAIM) layer is introduced to replace the traditional dielectric WAIM, improving the beam scan performance and reducing the antenna profile. The simulation shows that the proposed antenna array can operate over 2.4-12.4 GHz, approximately 5:1 bandwidth with maximum scanning angle of 50o for both E plane and 45o for H plane. The antenna profile above the ground is only 0.578λH at the highest operating frequency. This antenna array can find its application in the forthcoming massive MIMO beamforming systems for 5G.

Design of a New UWB Differential Tightly Coupled Dipole Array (D- TCDA)

Multifunctional arrays (MFAs) are widely used in RF electronic warfare, communications, radar, and sensing applications. Improvements in cooling technologies, high density packaging and ultra-wideband (UWB) transceivers are creating a paradigm shift in RF systems toward these MFAs. Another key enabler of these technologies is the use of UWB array apertures, which were impossible to design decades ago. In this paper, we present a new addition to the tightly coupled dipole array (TCDA) family that utilizes a patented UWB differential feed.

Optimized Differential TCDA (D-TCDA) With Novel Differential Feed Structure

Modern phased arrays require large instantaneous bandwidths, wide fields of view, and low profiles to conduct multiple functions. Many of these phased arrays rely on emerging high speed ADCs and advanced balanced transceivers. The benefits of balanced front-ends include improved linearity, dynamic range, isolation, and noise resilience. The application of a differential phased array in such a system removes extraneous losses caused by baluns, though the issue of feed-borne E-plane scan resonances must be considered. We address the E-plane scan resonance issue through an improved Balanced Wideband Impedance Transformer (BWIT) feed for the ultra-wideband (UWB) Tightly Coupled Dipole Array (TCDA). This BWIT feed has already demonstrated mitigated common-modes over a 3:1 bandwidth ratio while scanning to low angles. Here, our differential TCDA (D-TCDA) is developed for the L-C band ( viz. 1.0 GHz to 6.1 GHz) with emphasis on resonance-free wide-angle scanning. Rigorous EM model and circuit analysis is included to verify the BWIT performance. Under a VSWR $8\times 8$ single-polarized prototype.

Deployable Rigid-Flexible Tightly Coupled Dipole Array (RF-TCDA)

An origami-based Tightly Coupled Dipole Array (TCDA) is proposed for small satellite applications. The array is formed by a two-layered structure using rigid and flexible substrates to enable accordion-like folding. The proposed TCDA operates across 0.4-2.4 GHz with VSWR < 3 at broadside and across 0.6-2.4 GHz with VSWR < 3 when scanning down to 45∘ in the E-, D-, and H-plane. An 8 × 8 prototype was fabricated using Kapton Polyimide and FR4 and tested to verify the bandwidth and gain of the origami array. The fabricated prototype was demonstrated to be packable, low-profile, and lightweight (only 1.1kg). Notably, when packed, the array has a one-dimensional size reduction of 75%. As will be discussed, the packing compression is made possible by eliminating vertical PCB boards and incorporating the balun feeds within the dipole layer. To our knowledge, this is one of the first foldable, low profile, and low-scanning ultra-wideband arrays in the literature.

A Low-Cost Light-Weight Ultrawideband Wide-Angle Scanning Tightly Coupled Dipole Array Loaded With Multilayer Metallic Strips

This article presents a new ultrawideband wide-angle scanning tightly coupled dipole array loaded with multilayer metallic strips. The loaded multilayer metallic strips, which is composed of several narrow strips with different lengths, are used to equivalent the metal patch which has a specific shape. It can help achieve smoother impedance transform from the dipole to the free space. An equivalent circuit model (ECM) of the unit cell is proposed to help analyze and design the tightly coupled dipole array. Thanks to the loaded multilayer metallic strips, the array can be fed by a simple feeding structure, avoiding a matching network located below the ground plane. Also, all components of the proposed array are printed on a single dielectric substrate, resulting in a low-cost and light-weight array. The proposed tightly coupled dipole array can achieve 6.2:1 bandwidth with voltage stand wave ratio (VSWR) <; 3 while scanning to ±60° in all planes. The total profile of the array is 0.13 wavelength at 1.4 GHz. Finally, an 8×8 prototype is fabricated and measured. The measured results prove the feasibility of the design.

VHF/UHF Ultrawideband Tightly Coupled Dipole Array for CubeSats

To date, CubeSat radars and imagers have been limited to operations beyond S-band due to the challenges associated with the design of wideband, compact, low-frequency antennas. Concurrently, the frequencies at VHF/UHF bands can image through clouds and foliage, and are very attractive for ice, water and biomass sensing. There is thus a need to develop wideband antennas that can operate at VHF/UHF bands which are low cost, light-weight, and packable. In this paper, we present a CubeSat deployable Tightly Coupled Dipole Array (TCDA) that achieves VSWR<; 3 from 80 MHz - 600 MHz, and VSWR<; 4 from 65 MHz - 600 MHz. While the array itself is 1.2 m in length, 10 cm in width and 1.5 mm in thickness, it can be folded and stowed in a compact volume of 0.40U. We detail the design of the array, demonstrate the folding mechanism, and validate its performance through measurements.

Semi-Resistive Approach for Tightly Coupled Dipole Array Bandwidth Enhancement

A new approach to enhance the bandwidth of Tightly Coupled Dipole Arrays (TCDA) is presented. The new design achieves the integration of a semi-resistive Frequency Selective Surface network (FSS) composed of a non-resistive low-pass FSS and two resistive band-stop FSSs. The integration of this FSS network within a dual-polarized Tightly Coupled Dipole Array (TCDA) led to an increased impedance bandwidth of 28:1 from 0.20GHz to 5.6GHz. Notably, the use of an FSS superstrate allowed for scanning down to 60° at VSWR $12 \times 12$ array prototype was fabricated and tested to verify the bandwidth and gain of a finite array. The simulated radiation efficiency was demonstrated to be 83%, on average, across the band.

Coupled electric and magnetic dipole formulation for planar arrays of particles: Resonances and bound states in the continuum for all-dielectric metasurfaces

The optical properties of infinite planar array of scattering particles, metasurfaces and metagratings, are attracting special attention lately for their rich phenomenology, including both plasmonic and high-refractive-index dielectric meta-atoms with a variety of electric and magnetic resonant responses. Herein we derive a coupled electric and magnetic dipole (CEMD) analytical formulation to describe the reflection and transmission of such periodic arrays, including specular and diffractive orders, valid in the spectral regimes where only dipolar multipoles are needed. Electric and/or magnetic dipoles with all three orientations arising in turn from a single or various meta-atoms per unit cell are considered. The 2D lattice Green function is rewritten in terms of a 1D (chain) version that fully converges and can be easily calculated. Modes emerging as poles of such lattice Green function can be extracted. This formulation can be applied to investigate a wealth of plasmonic, all-dielectric, and hybrid metasurfaces/metagratings of interest throughout the electromagnetic spectrum.

Design of a Wideband Coupled Feed Dipole Antenna for PCL Array Systems

This article proposes the design of a wideband coupled feed dipole antenna for Passive Coherent Location (PCL) systems. The proposed antenna consists of an internal direct feed dipole and an external coupled feed dipole. This coupled feed mechanism, which is often used in microstrip patch antennas, is applied to the dipole element for a wide matching bandwidth. To verify the operating principle of the proposed antenna, an equivalent circuit model is investigated along with some parametric studies of the coupling effect. The proposed antenna is then extended to an eight-element uniform circular array to confirm the beamforming performance for PCL systems. The results demonstrate that the coupled feed dipole element is more suitable to enhance the matching bandwidth compared to a conventional dipole antenna.

Sparsely Excited Tightly Coupled Dipole Arrays Based on Irregular Array Techniques

An innovative architecture for sparsely excited tightly coupled dipole arrays is proposed, based on the irregular array techniques. In such a framework, an improved maximumentropy model considering the difference of embedded element patterns is applied to optimize the irregular partition to suppress the grating lobes. Meanwhile, guidelines for the entire design procedure including antenna elements, power dividers, and optimization design of irregular feeding networks are presented. In order to achieve large elevation angle scanning, the differential evolution (DE) algorithm is used to synthesize active pattern and active reflection coefficient simultaneously. Finally, a 192-port prototype operating at 8-12 GHz has been fabricated and measured, where the port spacing is 0.576λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> is the free-space wavelength at the highest frequency). Numerical and experimental results show that the prototype array is able to achieve the reduction of gain <; 1 dB for scanning to near broadside and about 2.7 dB for scanning up to 60°, in comparison with that of conventional Taylor arrays.

Dual‐polarised wideband tightly coupled dipole array for airborne applications

An ultra-wideband (UWB) array is presented for UHF-S band (0.19–2.3 GHz) communications with an emphasis on dual-linear polarisation and wide-angle scanning. The array achieves 12:1 impedance bandwidth for a voltage standing wave ratio (VSWR) <3 at broadside with low-angle scanning off broadside to 0°, 45°, 60° in the E-plane (VSWR < 3, 4, 3.1) and 0°, 45°, 60° (VSWR < 3, 3.8, 5.5) in the H-plane. A 7 × 11 prototype was fabricated and tested for verification. In addition, finite effects with respect to mounting UWB arrays in airborne platforms are discussed. Specifically, the effect of radomes, perfect electric conductor shielding walls and resistive walls on the gain of the designed tightly coupled dipole antenna was studied, showing that losses can approach 2 dB.

In-Band Scattering Control of Ultra-Wideband Tightly Coupled Dipole Arrays Based on Polarization-Selective Metamaterial Absorber

With the polarization-selective metamaterial absorber (PSMA), a unique approach for reducing the in-band radar cross section (RCS) while preserving the radiation performance of a tightly coupled dipole array (TCDA) is proposed. The proposed PSMA structure is comprised of resistive films, dielectric layers, and polarization gates. In detail, the resistive films are loaded on the surface of a TCDA, and the polarization gates are utilized to broaden the absorption bandwidth of PSMA as well as to improve the polarization purity of the array. Moreover, the process of the co-design of the phased array with PSMA is presented. The designed infinite array is able to achieve a 3:1 bandwidth from 6 to 18 GHz with the active VSWR $10 \times 10$ single-polarized prototype array is fabricated and measured. Measured results are in good agreement with simulated ones, thus demonstrating that the PSMA structure is able to reduce the scattering significantly throughout the operating band of the array under normal and oblique incidence.

An Optimal Radiation Pattern Synthesis and Correction of Mutually Coupled Circular Dipole Antenna Array

Abstract – This paper proposes a fundamental approach for radiation pattern correction of the mutually coupled circular dipole antenna array (CDAA) using parametric assimilation technique. The effect of mutual coupling is an indispensable part of any practical design issue of the antenna array. Many analytical and numerical techniques have been put forward in the past few decades for the calculation, compensation and reduction of mutual coupling effect. This paper shows an accurate method for mutual coupling correction by using a recently proposed technique called parametric assimilation technique, where the values of mutual impedance are calculated and assimilated with the values of the desired radiation pattern. The proposed technique is cost-effective, less complicated and easy to implement while achieves better performance for mutually coupled circular dipole antenna array synthesis. Grey Wolf Optimization (GWO) algorithm is a state-of-the-art stochastic algorithm applied here to find the optimal values of the current excitation weights and the inter-element spacing between each element of the CDAA for the desired, uncorrected and corrected far-field radiation pattern synthesis. PSO and DE optimization-based statistical results are also reported to compare the results obtained by using GWO algorithm to confirm the outstanding performance of GWO algorithm based design.

Efficient Design of Tightly Coupled Dipole Array Using an Equivalent Circuit-Based Approach

This paper proposes an efficient and systematic design approach for tightly coupled dipole array (TCDA) designs. In this approach, the radiator structure and feeding structure are designed and optimized based on their equivalent circuit models (ECM) respectively. A novel ECM is proposed to accurately describe the impedance characteristics of the radiator structure with dual-diamond dipoles. The proposed ECM of the radiator structure keeps its accuracy for variable design parameters. The ECM of the proposed feeding structure is also developed to analyze its impedance characteristics. As compared with conventional brute-force optimizations based on full-wave simulations, the two ECMs make it easy and efficient to design wideband TCDAs. A dual-polarized TCDA is designed with the proposed approach to illustrate the efficiency of the approach. The resultant TCDA operates in a wide frequency band of 0.87-10.14 GHz with VSWR ≤2 for broadside radiation. Meanwhile, the VSWR value under all conditions (broadside, ±60° scanning in E- and H-planes) remains ≤3 over the frequency band of 0.8-9 GHz. A 10 × 10 prototype is fabricated to demonstrate the design.

Cooperative interactions between nano-antennas in a high-Q cavity for unidirectional light sources

We analyse the resonant mode structure and local density of states in high-Q hybrid plasmonic-photonic resonators composed of dielectric microdisks hybridized with pairs of plasmon antennas that are systematically swept in position through the cavity mode. On the one hand, this system is a classical realization of the cooperative resonant dipole–dipole interaction through a cavity mode, as is evident through predicted and measured resonance linewidths and shifts. At the same time, our work introduces the notion of ‘phased array’ antenna physics into plasmonic-photonic resonators. We predict that one may construct large local density of states (LDOS) enhancements exceeding those given by a single antenna, which are ‘chiral’ in the sense of correlating with the unidirectional injection of fluorescence into the cavity. We report an experiment probing the resonances of silicon nitride microdisks decorated with aluminium antenna dimers. Measurements directly confirm the predicted cooperative effects of the coupled dipole antennas as a function of the antenna spacing on the hybrid mode quality factors and resonance conditions.

A Low-Profile Wideband Tightly Coupled Dipole Array With Reduced Scattering Using Polarization Conversion Metamaterial

A novel approach aimed at reducing the out-of-band scattering cross section (SCS) and preserving the radiation characteristics of a low-profile wideband tightly coupled dipole array (TCDA) operating in P-L band is presented. The array is designed without wide-angle impedance matching (WAIM) layers for low profile and simple topological structure. The SCS reduction of the proposed TCDA is achieved by loading the array with polarization conversion metamaterial (PCM). The PCM is arranged in a chessboard configuration and placed on the ground plane of the TCDA. The infinite array is able to achieve a 4:1 bandwidth from 0.5 to 2.0 GHz, with VSWR $8 \times 8$ TCDA prototype is fabricated and measured. The experimental results are in good agreement with simulated results. The simulated and experimental results demonstrate that by using the proposed approach with PCM, the monostatic SCS is significantly reduced within 6.0–18.0 GHz under normal incidence. Meanwhile, the radiation characteristics are well preserved in the operating band of the TCDA.

Low-Profile, Lightweight, Ultra-Wideband Tightly Coupled Dipole Arrays Loaded With Split Rings

An ultra-wideband and wide-scanning tightly coupled dipole array with low-profile height and lightweight is presented. A novel split ring (SR) printed on planar single-layer printed circuit board is designed and loaded on each element of the proposed array to replace the conventional wide-angle impedance matching (WAIM) superstrates, which usually consist of dielectric slabs. Consequently, the array achieves a 7.2:1 impedance bandwidth (0.3–2.15 GHz) while scanning up to 70° in the E-plane and 45° in the H-plane for active VSWR $8 \times 8$ prototype array weighing only 4.3 kg (including an aluminum ground plane of 2.3 kg) was fabricated. The measured results are in good agreement with the simulated results.