Coupled Antenna Array Research Articles

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.

Design of X-band ultra-wide angle scanning phased array antenna

–To realize X-band ultra-wide-angle scanning, the paper proposes a novel tightly coupled array antenna unit design, and combines the equivalent circuit to analyze and optimize antenna parameters. With the integrated Marchand balun, dipole and balun can be fabricated on the same PCB, thus reducing antenna’s weight and cost. Introducing the vertical parasitic superstrate and horizontal dielectric layer above the antenna aperture, the two work together to improve the impedance transformation during wide-angle scanning. The results show that the scanning angle ranges up to 80° in E-plane while 70° in H-plane, with an active VSWR<3, in X-band (8–12 GHz). The antenna is simple, compact and easy to fabricate.

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.

A Wideband Low-Profile Tightly Coupled Antenna Array With a Very High Figure of Merit

A wideband, low-profile, tightly coupled antenna array with a simple feed network is presented. The dipole and feed networks in each unit cell are printed on both sides of a single RT/Duroid 6010 substrate with a relative dielectric constant of 10.2. The feed network, composed of meandered impedance transformer and balun sections, is designed based on Klopfenstein tapered microstrip lines. The wide-angle impedance matching is empowered by a novel wideband metasurface superstrate. For the optimum design, scanning to 70° along the E-plane is obtained together with a very high array figure of merit PA = 2.84. The H-plane scan extends to 55°. The broadside impedance bandwidth is 5.5:1 (0.80–4.38) GHz with an active voltage standing-wave ratio value ≤2. The overall height of the array above the ground plane is $0.088\lambda _{\mathrm {L}}$ , where $\lambda _{\mathrm {L}}$ is the wavelength at the lowest frequency of operation. A prototype was fabricated and tested to confirm the design concepts.

Synthesis and Optimization of Almost Periodic Antennas Using Floquet Modal Analysis and MoM-GEC Method

This paper presented a new Floquet analysis used to calculate the radiation for 1-D and 2-D coupled periodic antenna systems. In this way, an accurate evaluation of mutual coupling can be proven by using a new mutual interaction expression that was based on Fourier analysis. Then, this work indicated how Floquet analysis can be used to study a finite array with uniform amplitude and linear phase distribution in both x and y directions. To modelize the proposed structures, two formulations were given in a spectral and spatial domain, where the Moment (MoM) method combined with a generalized equivalent circuit (GEC) method was applied. Radiation pattern of coupled periodic antenna was shown by varying many parameters, such as frequencies, distance and Floquet states. The 3-D radiation beam of the coupled antenna array was analyzed and compared in several steering angles θs and coupling values dx. The simulation of this structure demonstrated that directivity decreased at higher coupling values. The secondary lobs in the antenna radiation pattern affected the main lobe gain by energy dispersal and considerable increasing of side lobe level (SLL) may be achieved. Therefore, the sweeping of the radiation beam in several steering directions affected the electromagnetic performance of the antenna system: the directivity at the steering angle θs = π⁄3 was more damaged and had 19.99 dB while the second at θs = 0 had about 35.11 dB. This parametric study of coupled structure used to concept smart periodic antenna with sweeping radiation beam.

Phased Array Antenna Handbook (Third Edition) [Book Review

The third edition of the Array Antenna Handbook is a very welcome addition to the antenna field. It brings together many ideas and techniques that one would normally have to search through the literature to find. The book is a comprehensive treatment of phased array antennas written by a single author, and it is thus an integrated text that flows smoothly from one topic to another. The publication does not contain homework problems, but the material is presented in such a sufficiently explanatory manner that it could be used as a textbook for a course on phased or antenna arrays, in general, or as a supplement to a course on antennas. The book contains nine chapters, and it has a total length of 530 pages. The text focuses on the antenna aspects of phased arrays and, thus, focuses on aspects related to the radiation patterns of a phased array, along with the antenna elements that are used in phased arrays, and other antenna-related concepts such as mutual coupling in antenna arrays (and their associated effects on scan behavior such as scan blindness). Phased arrays are steadily gaining in relevance with applications in 5G and many other systems, both military and commercial. Better affordability and a wider variety of applications ensures this positive trend. Subsequently, this third edition is a most welcome addition to the antennas and propagation community. This latest edition has been updated to include new contributions to scanning antennas based on reflectors and lenses, as well as thinned arrays, and a more contemporary presentation of numerical methods for pattern synthesis has also been provided. The book provides a comprehensive coverage of all aspects of phased arrays from an antenna point of view, and it also provides an excellent overview of systemlevel aspects of phased arrays in the first chapter. It is very well written by a leading expert in the field, and it is one of the few texts written entirely on phased arrays. As such, it is a must-have publication for every antenna engineer, system engineer, scientist, or practitioner who works with or is interested in phased arrays. This book will also make a great supplement for instructors who teach a course in antenna engineering and who wish to cover phased arrays as part of their course topics.

Synthesis of coupled antenna arrays using digital phase control via integer programming

A pattern synthesis technique for real and coupled antenna arrays by using digital phase-only excitation weights is introduced here. The method is formulated as an integer linear programming problem incorporating a fast full-wave analysis of the array, based on the finite element method and spherical mode expansions. The method achieves radiation patterns with specified pointing directions, main lobe widths, minimum sidelobe level, and prescribed nulls, controlled by digital phase shifters.

An Ultra-Wide-Band Tightly Coupled Dipole Reflectarray Antenna

A novel ultra-wide-band tightly coupled dipole reflectarray (TCDR) antenna is presented in this paper. This reflectarray antenna consists of a wideband feed and a wideband reflecting surface. The feed is a log-periodic dipole array antenna. The reflecting surface consists of $26 \times 11$ unit cells. Each cell is composed of a tightly coupled dipole and a delay line. The minimum distance between adjacent cells is 8 mm, which is about 1/10 wavelength at the lowest operating frequency. By combining the advantages of reflectarray antennas and those of tightly coupled array antennas, the proposed TCDR antenna achieves ultra-wide bandwidth with reduced complexity and fabrication cost. A method to minimize the phase errors of the wideband reflectarray is also developed and the concept of equivalent distance delay is introduced to design the unit cell elements. To verify the design concept, a prototype operating from 3.4 to 10.6 GHz is simulated and fabricated. Good agreement between simulated and measured results is observed. Within the designed frequency band, the radiation pattern of the TCDR antenna is stable and the main beam of the antenna is not distorted or split. The side lobe levels of the radiation patterns are below −11.7 dB in the entire operating band. It is the first time a tightly coupled reflectarray is reported.

Measurement Technique to Emulate Signal Coupling Between Power Amplifiers

A measurement technique to emulate coupling between power amplifiers (PAs) such as that in an antenna array is presented. The case that the technique aims to emulate is referred to as the target array. The technique provides emulation of the distorted output signal for each PA under the coupling effect without the requirement for constructing the target physical coupling network or antenna array. Furthermore, given that the target array contains identical elements or PAs, transmitting either identical or different signals, the technique merely requires one PA as the device-under-test (DUT) to produce all output signals. The technique has direct connection to active load–pull, and aims to present the output of the DUT with corresponding time-varying impedances of each transmission path in the target array. The emulated output signals can then be analyzed, for example, in terms of adjacent channel power ratio, error vector magnitude, and normalized mean square error. Such measurement technique provides insight into the distortion and the impairment generated in the target array without the requirement to realize an actual array, and can be used, as an example, during the design stage of an array. The technique is theoretically motivated. The procedure is thoroughly described. The technique is experimentally demonstrated and verified under various usage cases and scenarios. Subsequent comparison to conventional active load–pull is provided.

A Capacitive Coupled Patch Antenna Array With High Gain and Wide Coverage for 5G Smartphone Applications

In this paper, a novel capacitive coupled patch antenna array capable of providing high gain and 360° coverage in the elevation plane is proposed. The proposed antenna element is studied in detail using the theory of characteristic modes to enhance the bandwidth. It exhibits a uniform radiation pattern with a stable gain when integrated with the mobile phone chassis. These elements are positioned in the mobile phone chassis as a set of four sub-arrays each with 12 antenna elements to provide high realized gain around 16.5 dBi with each sub-array providing 90° coverage. The antenna array is fabricated, and the beam steering performance of the array is evaluated using a beam-steering test bed. The results show that it covers the frequency range of 24–28 GHz, which is a promising band for future 5G-based smartphone services as predicted and could be a strong candidate for 5G applications.

Tightly Coupled Array Antennas for Ultra-Wideband Wireless Systems

Tightly coupled array (TCA) antenna has become a hot topic of research recently, due to its potential of enabling one single antenna array to operate over an extremely wide frequency range. Such an array antenna is promising for applications in numerous wideband/multi-band and multi-function wireless systems such as wideband high-resolution radars, 5G mobile communications, satellite communications, global navigation satellite systems, sensors, wireless power transmission, Internet of Things, and so on. Many papers on this topic have been published by researchers internationally. This paper provides a detailed review of the recent development on TCA that utilizes the capacitive coupling. The basic principles and the historical evolution of the TCAs are introduced first. Then, recent development in the analysis and design of TCAs, such as equivalent circuit analysis, bandwidth limitation analysis, array elements, feed structures, substrates/superstrates loading, and so on, are explained and discussed. The performances of the state-of-the-art TCAs are presented and a comparison amongst some TCAs reported recently is summarized and discussed. To illustrate the practical designs of TCA, one case study is provided, and the detailed design procedures of the TCA are explained so as to demonstrate the TCA design methodology. Simulated results including the VSWR at different angles of scanning, patterns, and antenna gain are shown and discussed. A conclusion and future work are given in the end.

Investigations on Dual Slant Polarized Cavity-Backed Massive MIMO Antenna Panel With Beamforming

A cavity-backed dual slant polarized and low mutual coupling antenna array panel with frequency band from 4.9 to 6 GHz is analyzed and realized for the MIMO antenna 5G applications. The beamforming capability of this array is also explored. The printed cross dipoles fed with balun and enclosed in a cavity are used as radiating elements. The two cross dipoles are placed at an angle of 45° and 135° giving slant polarizations. A $4 \times 4$ subarray of dimension $2.8\lambda \times 2.8\lambda \times 0.26\lambda $ where $\lambda $ is free space wavelength at 6 GHz is designed, fabricated, and experimentally verified. It shows good impedance matching, port isolation, envelope correlation coefficient, and radiation characteristics which are desired for MIMO applications. Beamforming capability in the digital domain is verified using the Keysight SystemVue simulation tool for both $4 \times 4$ and $16\times 16$ panel arrays which employ measured 3-D embedded element radiation pattern data of the fabricated $4 \times 4$ subarray. Four simultaneous beams using digital beamforming approach are also presented for the $16 \times 16$ array for multiuser environment base station antenna applications.

Novel Decoupling Concept for Strongly Coupled Frequency-Dependent Antenna Arrays

This paper presents a novel wideband decoupling network for strongly frequency-dependent antenna couplings. The network consists of directional couplers, a transmission line, and a parallel resonant circuit. It cancels mutual coupling by the superposition of a designed coupling with the same magnitude as the original coupling but the opposite phase. Further, the proposed approach accommodates variations in the coupling magnitude and large group delays in the coupling phase. Therefore, it is easy to apply the approach to wideband applications. The design formulas are also derived. With these formulas, the computational results show that the resultant coupling with the proposed technique is 26.4 dB smaller than that of the original coupling at 12.2% bandwidth with a large group delay. Moreover, this paper also describes a technique for practical implementation using short stubs. The resultant coupling with the fabricated multiantenna is 12.6 dB smaller than the original, over the entire 12.2% frequency range. The degradation of radiation efficiency by the proposed circuit is sufficiently small and the enhancement of signal-to-noise ratio is demonstrated.

Robust Nonlinear Array Interpolation for Direction of Arrival Estimation of Highly Correlated Signals

Important signal processing techniques need that the response of the different elements of a sensor array have specific characteristics. For physical systems this often is not achievable as the array elements’ responses are affected by mutual coupling or other effects. In such cases, it is necessary to apply array interpolation to allow the application of ESPRIT, Forward Backward Averaging (FBA), and Spatial Smoothing (SPS). Array interpolation provides a model or transformation between the true and a desired array response. If the true response of the array becomes more distorted with respect to the desired one or the considered region of the field of view of the array increases, nonlinear approaches become necessary. This work presents two novel methods for sector discretization. An Unscented Transform (UT) based method and a principal component analysis (PCA) based method are discussed. Additionally, two novel nonlinear interpolation methods are developed based on the nonlinear regression schemes Multivariate Adaptive Regression Splines (MARS) and Generalized Regression Neural Networks (GRNNs). These schemes are extended and applied to the array interpolation problem. The performance of the proposed methods is examined using simulated and measured array responses of a physical system used for research on mutual coupling in antenna arrays.

Mathematical Modeling of n-Sided Polygon Metamaterial Split Ring Resonators for 5.8 GHz ISM Band Applications

Metamaterials have become an interesting area of research in electromagnetism due to their unique characteristics which can radically change the world of wireless communication. Split ring resonator (SRR) is the most commonly used metamaterial structure which is used for preventing signal propagation at the desired frequency band due to its capability to exhibit negative permeability and stop band characteristics. This paper presents SRR designs for 5.8 GHz industrial, scientific and medical band applications. Rings of the designed SRRs are n-sided regular polygons. We have proposed a mathematical model for the SRR to estimate the shape of SRR for given values of coupling and bandwidth at 5.8 GHz. Subsequently, mathematical equations are proposed for the estimation of coupling and bandwidth from given shape of SRR for 5.8 GHz band. Proposed SRR designs and their mathematical models find applications in the areas such as reduction of mutual coupling in antenna arrays and design of microwave band stop filters.

Low mutual coupling antenna array for WLAN application

A mutual coupling reduction antenna design for WLAN MIMO application is proposed. The proposed antenna array consists of two rectangular patch antennas, six parallel metal strips, a single substrate layer, and common ground plane. About −42 dB mutual coupling is achieved at the 5.8 GHz resonant frequency. Both simulation and measurement results confirm improvements in mutual coupling at about 30 dB when compared with those without metal strips. The radiation patterns are almost unaffected by adding these metal strips in the proposed antenna.

A dual band stacked aperture coupled antenna array for WLAN applications

ABSTRACTIn this article, a dual band stacked micostrip antenna array is presented for wireless local area network. The antenna is designed and simulated using CST MWSv’14. Stacking of the patches is done to achieve dual band. Further resonant slots are cut on the patch to achieve greater bandwidth. The antenna uses aperture coupled feed with defected ground structure on reduced ground. The antenna is fabricated on FR4 substrate with a dielectric constant of 4.4. The simulated antenna shows a bandwidth of 228.3 MHz from 3.63 to 3.86 GHz and 232 MHz from 5.15 to 5.38 GHz. The simulated gain and envelope correlation coefficient was found to be 6.11 dB and 0.14. The testing of the prototype antenna (to measure S11) is done using vector network analyser. The measured results are matching to the simulated ones. The simulated and the measured results are presented in the article. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:648–654, 2017

Pattern Synthesis of Coupled Antenna Arrays via Element Rotation

In this work, a pattern synthesis method is presented for coupled antenna arrays via element rotation. The array is rigorously analyzed with a hybrid and full-wave analysis method based on the 3-D finite element method, modal analysis, generalized scattering matrix, and rotation and translation properties of spherical waves, including mutual coupling effects. The co- and cross-polar components are optimized by means of a gradient method, according to a specific cost function, via successive rotations of the elements.

Corrigendum to “The Noise Performance of a Multiple-Input-Port and Multiple-Output-Port Low-Noise Amplifier Connected to an Array of Coupled Antennas”

Corrigendum to “The Noise Performance of a Multiple-Input-Port and Multiple-Output-Port Low-Noise Amplifier Connected to an Array of Coupled Antennas”

Radiation Pattern Correction in Mutually Coupled Antenna Arrays Using Parametric Assimilation Technique

Mutual coupling in antenna arrays has been a deterrent issue for design accuracy and predictions. Several techniques for calculation, reduction, and compensation of mutual coupling were proposed in the past; the techniques include both analytical and numerical approaches. However, the methods of mutual coupling mitigation in context of radiation pattern correction had been very few. Here, mutual impedances are calculated through a conventional technique and is used to form a set of network equations whose parameters are assimilated with those of a desired radiation pattern; the proposed technique directly leads to the calculation of feed currents, required in the antennas, for restoring the mutual coupling affected radiation pattern to the desired pattern. The technique is accurate with lesser computational complexity compared with the extant methods.