Linear Dipole Array Research Articles

An ultra-wideband 1-D monopulse antenna based on tightly coupled dipole linear array

A low-profile and ultra-wideband (UWB) 1-D monopulse antenna based on the tightly coupled dipole linear array (TCDLA) is proposed in this paper. First, a compact UWB monopulse feeding network is discussed. It consists of a UWB monopulse comparator and a pair of miniaturized 1-to-4 power dividers with tapered baluns. Then, a TCDLA element with frequency selective surfaces (FSS) superstrates is designed for radiation. Meanwhile, the feeding network is arranged at the bottom layer to avoid spurious radiation on radiation patterns. Finally, by connecting the feeding network and radiation part, a UWB monopulse antenna prototype is fabricated and measured. The proposed monopulse antenna array achieved an 82.35% (5-12 GHz) shared bandwidth and the isolation is greater than 16 dB. The measured results are in good agreement with the simulated results.

Linear Dipole Array With Element Rotation for Enhanced DOA and Polarization Estimation

Linear Dipole Array With Element Rotation for Enhanced DOA and Polarization Estimation

Backward THz Emission from Two-Color Laser Field-Induced Air Plasma Filament.

Two-color laser field-induced plasma filaments are efficient broadband terahertz (THz) sources with intense THz waves emitted mainly in the forward direction, and they have been investigated intensively. However, investigations on the backward emission from such THz sources are rather rare. In this paper, we theoretically and experimentally investigate the backward THz wave radiation from a two-color laser field-induced plasma filament. In theory, a linear dipole array model predicts that the proportion of the backward emitted THz wave decreases with the length of the plasma filament. In our experiment, we obtain the typical waveform and spectrum of the backward THz radiation from a plasma with a length of about 5 mm. The dependence of the peak THz electric field on the pump laser pulse energy indicates that the THz generation processes of the forward and backward THz waves are essentially the same. As the laser pulse energy changes, there is a peak timing shift in the THz waveform, implying a plasma position change caused by the nonlinear-focusing effect. Our demonstration may find applications in THz imaging and remote sensing. This work also contributes to a better understanding of the THz emission process from two-color laser-induced plasma filaments.

Synthesis of uniform amplitude sparse linear dipole arrays with multiple shaped‐beam patterns by sharing element rotations and positions

In this article, a novel method of synthesizing sparse linear dipole arrays with multiple shaped-beam patterns is proposed by finding a set of common element rotations and positions along with individual excitation phases. Compared with most shaped multiple-pattern synthesis methods using nonuniform amplitude excitations, the proposed method adopts the uniform amplitude excitation and exploits the element rotation as a supplementary degree of array freedom. Such a method enables each amplifier to work at its optimal level and avoids the usage of unequal power dividers for the array feeding network, thus reducing the cost, space, and weight of the radiation system. The shaped multiple-pattern synthesis problem with multiple constraints including the peak sidelobe level, cross-polarization level, minimum element spacing, and array length is formulated and optimized by particle swarm optimization. Two examples for synthesizing sparse linear dipole arrays with multiple shaped-beam patterns are conducted to validate the effectiveness and superiority of the proposed method. Synthesis results show that the proposed method can save antenna elements and avoid the usage of unequal power dividers for test cases. Moreover, the full-wave simulations are also conducted in these two examples.

DOA Estimation of Linear Dipole Array With Known Mutual Coupling Based on ESPRIT and MUSIC

AbstractIn this paper, multiple signal classification and estimation of signal parameters via rotational invariance technique (ESPRIT) algorithms are proposed to estimate the direction of arrival (DOA) of multiple incident signals under known mutual coupling among elements of the antenna array. These algorithms use the same subspace based techniques to achieve the separation of the eigenvectors into two subspaces: the signal space and the noise space. However, ESPRIT only uses the signal space. The performance of subspace based DOA estimation algorithm is evaluated using uniform linear arrays of dipole elements. The simulation results show the exact number of samples and elements, signal‐to‐noise ratio and spacing between the antennas elements used are the most important parameters in the algorithms, to sustain the accuracy of the DOA of the incident signals. The problem of calculating mutual coupling coefficient of the array elements is formed into a matrix has been considered. It is shown from the simulation results that the performance of the DOA estimation techniques considering the mutual coupling effect can be improved by the proposed compensation method. The different results obtained are in good agreement with those of the literature.

Adaptive Beamforming Algorithm Based on MVDR for Smart Linear Dipole Array with Known Mutual Coupling

Adaptive Beamforming Algorithm Based on MVDR for Smart Linear Dipole Array with Known Mutual Coupling

Capacity Bounds and Degrees of Freedom for MIMO Antennas Constrained by Q-Factor

The optimal spectral efficiency and number of independent channels for MIMO antennas in isotropic multipath channels are investigated when bandwidth requirements are placed on the antenna. By posing the problem as a convex optimization problem restricted by the port Q-factor a semi-analytical expression is formed for its solution. The antennas are simulated by method of moments and the solution is formulated both for structures fed by discrete ports, as well as for design regions characterized by an equivalent current. It is shown that the solution is solely dependent on the eigenvalues of the so-called energy modes of the antenna. The magnitude of these eigenvalues is analyzed for a linear dipole array as well as a plate with embedded antenna regions. The energy modes are also compared to the characteristic modes to validate characteristic modes as a design strategy for MIMO antennas. The antenna performance is illustrated through spectral efficiency over the Q-factor, a quantity that is connected to the capacity. It is proposed that the number of energy modes below a given Q-factor can be used to estimate the degrees of freedom for that Q-factor.

Conditional and Unconditional Deterministic Bounds on the MSE of the Non-Uniform Linear Co-centered Orthogonal Loop and Dipole Array

The co-centered orthogonal loop and dipole (COLD) array exhibits some interesting properties, which makes it ubiquitous in the context of polarized source localization. In the literature, one can find a plethora of estimation schemes adapted to the COLD array. Nevertheless, their ultimate performance in terms the so-called threshold region of mean square error (MSE), have not been fully investigated. In order to fill this lack, we focus, in this paper, on conditional and unconditional bounds that are tighter than the well known Cramér-Rao Bound (CRB). More precisely, we give some closed form expressions of the McAulay-Hofstetter, the Hammersley-Chapman-Robbins, the McAulaySeidman bounds and the recent Todros-Tabrikian bound, for both the conditional and unconditional observation model. Finally, numerical examples are provided to corroborate the theoretical analysis and to reveal a number of insightful properties.

A Phased Array Antenna with New Elements Designed Using Source Transformations

Transformation electromagnetics/optics (TE/TO) has been shown to be a useful technique in designing electromagnetic devices with very unique properties. Here, the concepts of transformation optics for single elements is extended to an array of “pinwheel” shaped elements for the first time. Through full-wave finite element analysis (FEA), it is shown that a transformed “pinwheel” linear array can be designed to operate identically to a uniformly spaced linear dipole array. Thus, the “pinwheel” antenna array will maintain all the advantages of array processing of a simple dipole antenna array. The proposed method has applications in structurally integrated and conformal phased arrays for wireless communications, radars, and sensing where structural and mechanical constrains do not align with antenna performance.

Virtual Impedance Method for Mutual Coupling Compensation

The radiation pattern of an antenna within an array environment is modified by mutual coupling to neighboring elements, which can create unknown phase and amplitude variation on the order of 10° and 5 dB. This uncertainty in the element patterns results in beamforming errors, which can be particularly problematic for applications requiring precise pattern control. A new approach is reported to compensate for the mutual coupling of single-mode radiators using only the measured S-parameters and received signal from several far-field sources. The technique relies on the fact that dominant mode scattering from each antenna can be removed by terminating it with the proper impedance. Optimized beamforming weights are derived that compensate for mutual coupling. It is shown that implementing these optimized weights is equivalent to terminating all elements with a “virtual” impedance that cancels scattering from neighboring antenna elements (i.e., mutual coupling). Simulations of perfectly uniform and nonuniform linear dipole arrays show that compensating for mutual coupling using the proposed technique reduces the variation of the embedded element patterns by an order of magnitude compared to more conventional techniques. The proposed approach could be useful for a wide variety of antenna arrays and may even lend itself to self-calibration in the field using signals of opportunity.

A single‐layer high‐gain dipole antenna array with a bidirectional radiation pattern based on parallel‐strip line

A single-layer dipole antenna array with quasi-Yagi configuration has been proposed and demonstrated, which provides a dual radiation pattern with the same sense. This antenna is mainly composed of a substrate-supported parallel strip line (PSL) and several periodic dipole elements. Fed by PSL, dipole elements can be stimulated with a uniform power, forming a linear dipole antenna array. By adjusting the elements separation appropriately, the step phase of array factor can be tuned to achieve the same directivity as the element dipole. When an SubMiniature version A (SMA) coaxial connector is connected at the beginning of PSL, the fundamental mode TEM in the PSL is excited and the radiation electromagnetic wave from the dipole elements is achieved. A taper line between the SMA and PSL can be used to reduce the discontinuity, minimizing the reflection coefficient of the port. According to the theory of classical Yagi antenna, the gain can be further improved by introducing multiple directors, achieving the gain increment of about 3 dBi in the proposed design. Considering 5 GHz frequency band applications (4.85–5.2 GHz), the experimental and simulated results show the proposed antenna array has a working bandwidth ( | S 11 | ≤ − 10 d B ) from 4.85 to 12 GHz.

Multiple Solutions Starting from Real Shaped Beams in Equispaced Linear Arrays.

In the present work, the theoretical basis of the multiplicity of solutions obtained from an initial real symmetric distribution is derived. This initial solution is devoted to generating an equivalent pure real shaped-beam pattern for a concrete synthesis scenario. However, these new solutions are not based on real symmetric distributions; hence, not based on the generation of pure real patterns. The bandwidth performances and tolerance to errors provided by the multiple solutions in the array design are analyzed by considering different architectures, also including mutual coupling models and element factor expressions due to accuracy purposes. In addition, a technique to obtain efficient linear arrays by designing resonant structures is addressed. Examples involving both standard linear arrays of half-wavelength cylindrical dipoles and resonant linear arrays generating flat-top beam patterns are reported and discussed. Additionally, an extension to planar arrays performed by means of a generalisation of the Baklanov transformation through collapsed distribution techniques inspired in the well-known method devised by Tseng and Cheng is performed. In such a way, an analysis of the quality of solutions for generating circular and elliptical footprints with controlled both SLL and ripple which are highly interesting in the framework of space vehicle applications.

Characteristic Mode Analysis of ESPAR for Single-RF MIMO Systems

A systematic method based on the Theory of Characteristic Modes (TCM) for finding orthogonal radiation patterns of any electronically steerable parasitic array radiator (ESPAR) is described. This method can be useful for designing single-RF front-end multiple-input multiple-output (MIMO) systems in which orthogonal patterns can be utilized as a basis set for space modulation (SM) or full multiplexed MIMO systems. The method is based on the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> -port formulation of TCM and is not restricted to antenna type or array configuration. It can also provide closed formed solutions for the antenna element currents required to generate the orthogonal patterns. In addition an approach to finding the required load reactances in ESPAR for generating the orthogonal patterns is provided and is based on the quasi-Newton method utilizing a closed form expression for the initial approximate solution. Approximate estimation of the effective aerial degrees of freedom of the ESPARs is also discussed. Two simulation examples of ESPARs, a 4-element linear dipole array and an 8-element rectangular planar inverted-F antenna array, using SM as well as full multiplexed MIMO are provided, demonstrating the effectiveness of the proposed method.

Design of Sum and Difference Patterns by Optimizing Element Rotations and Positions for Linear Dipole Array

This communication presents a novel method of synthesizing both sum and difference patterns by optimizing the element rotations and positions for linear dipole array. The common element rotations and positions are optimized by using the particle swarm optimization (PSO) method to produce sum and difference patterns with reduced sidelobe levels (SLLs) and cross-polarization levels (XPLs) and as steep slope as possible for the difference pattern at the target direction. Such a method leads to a sum-and-difference array with sparsely distributed uniform amplitude elements, thus saving many antenna elements and unequal power dividers. Three examples for synthesizing sparse rotated dipole arrays with sum and difference patterns are provided. Synthesis results show that the obtained arrays with uniform amplitudes can produce the satisfactory sum and difference patterns while saving about 34.69% ~ 42.27% of the antenna elements compared with λ/2-spaced arrays occupying the same aperture.

Nonadditive properties of van der Waals interactions in a one-dimensional dipole array

The van der Waals potential energy of a linear dipole array is calculated based on a formula using a determinant of a matrix determining the dipole interactions, which includes all orders of the coupling strength and can be applied to a system with an arbitrary number of dipoles. To consider the nonadditivity of the van der Waals interactions, the van der Waals potential energy is expressed as a series of ratios of the susceptibility of the dipole to a cubic root of the distance between the nearest-neighboring dipoles, up to the fourth order for different numbers of dipoles. We show that the contribution of the terms including nonadditive interactions between four dipoles increases with the total number of dipoles and exceeds that between two dipoles. Furthermore, the error in the series expansion is evaluated by comparing the exact potential energy, including all orders of the coupling strength for a small number of dipoles.

Superdirective Linear Dipole Array Optimization

The theory of superdirective antenna arrays was discussed. The procedure for finding the excitation currents of fixed-geometry arrays, which maximizes the directivity, termed as superdirectivity, for a given direction and polarization, was described. The procedure was based on the solution of an eigenvalue problem including the directivity and matrices of normalized self- and mutual radiation intensities and normalized self- and mutual radiated powers of array elements. For examples of a linear dipole array located above a perfect electric conductor ground plane, this procedure was also combined with the optimization of the parameters of geometry of the array as a spacing of dipoles, or their height above the ground, for various number of dipoles in the array.

A Linear Array of Skewed Dipoles With Asymmetric Radiation Pattern for Angular Filtering

In this letter, we present a design of a linear array of tilted dipoles to achieve radiation patterns with asymmetric angular filtering characteristics. To realize the asymmetric radiation, the dipole elements are spaced by a distance larger than half a wavelength, thus allowing for grating lobes to occur in the visible region. Moreover, the dipoles are loaded with artificial dielectrics to increase the front-to-back ratio and consequently to enable higher gain in certain desired angular regions. Based on the design, a linear array with ten elements is manufactured and tested. The measured results show the ability of such an array to achieve stable gain from broadside up to 90° scanning while implementing a stopband angular filter for negative scanning angles.

Dynamic Metasurface Antennas for Higher-order MIMO Systems in Indoor Environments

We propose a MIMO system using a dynamic cavity-backed metasurface antenna (DMA) as a transmit antenna to improve the channel capacity of indoor MIMO channels. The DMA is a printed cavity loaded with tunable metamaterial radiators and fed by radio frequency ports. The DMA can generate radiation patterns that are adaptive to MIMO channels by individual tuning of the metamaterial radiators. In this letter, we study a 4 $\times $ 4 MIMO system operating at 5.9 GHz, consisting of a simulated DMA as transmit antenna and a linear dipole array as receive antenna. Using a ray tracing technique, we simulate indoor MIMO channels and compute MIMO channel capacity at different receiver locations. We demonstrate that the adaptive radiation pattern generated by the DMA can increase the channel capacity. The MIMO system using the DMA can be low cost and low in power consumption, and can find applications where bandwidth, power, and cost represent constraints.

Synthesizing Uniform Amplitude Sparse Dipole Arrays With Shaped Patterns by Joint Optimization of Element Positions, Rotations and Phases

This paper presents a novel method for synthesizing sparse dipole arrays with shaped patterns by joint optimization of element positions, rotations and phases. Such joint optimization exploits maximum available degrees-of-freedom under the assumption of uniform amplitude excitations to improve the shaped power pattern synthesis performance, and it leads to a reduced number of elements and simpler feeding network without using unequal power dividers for the array. The copolarization (COP) and cross-polarization patterns for a rotated dipole array are derived in a 2-D case, and then the vectorial shaped pattern synthesis problem is formulated as finding the optimal solution by maximally approaching the desired COP pattern shape under multiple constraints on the sidelobe level (SLL) and cross-polarization level (XPL). In addition, an asymmetric mapping method is incorporated into the proposed joint optimization, so that the minimum element spacing constraint can be also used for the synthesis of planar sparse dipole arrays. The comprehensive learning particle swarm optimization (CLPSO) algorithm is adopted to optimize the element positions, rotation angles and phases. A set of synthesis experiments including linear and planar rotated dipole arrays with a different pattern shape requirements are conducted to validate the effectiveness and robustness of the proposed approach. Synthesis results show that the proposed approach can save about 17.24% – 55.86% elements as well as many unequal power dividers for test cases.

Design and Development of High-Gain SIW H-Plane Horn Antenna Loaded With Waveguide, Dipole Array, and Reflector Nails Using Thin Substrate

In this communication, a new probe-fed substrate integrated waveguide (SIW) H-plane horn antenna including three linear dipole arrays is proposed. To feed the dipole arrays, a portion of a rectangular waveguide is placed at the front of the radiating aperture of the SIW horn in conjunction with two slots, which are etched at the top and bottom of the substrate. A row of reflector nails is also added to reduce the backward radiation and to improve the antenna gain. A prototype of the proposed antenna is fabricated using the printed circuit board process. The proposed antenna is numerically investigated by a software package. The simulated and measured results are reported for verification. The measured results show that the proposed antenna provides 13.97 dBi gain at 20.5 GHz with a low backward radiation.