Evolutionary optimization of Haferman carpet fractal patterned antenna array

This article investigates radiation characteristics of a new type of fractal shaped antenna array based on Haferman carpet geometry. An iterative feed matrix eases the complexity of array factor calculation that makes the array factor suitable for the application of any evolutionary optimization techniques. It is seen that Haferman carpet array produces peak side lobe level (PSLL) better than Sierpinski carpet that produces ?10 dB PSLL at every stage of growth. Optimization techniques have been applied for array element reduction and PSLL minimization at different stages of growth. Here, PSLL is minimized by turning off array elements and also by varying inter element spacing between the array elements. The optimized version of Haferman carpet array produces better characteristics (49.38% thinning with ?20.5 dB PSLL for stage‐2, 46.3% thinning with ?22 dB PSLL for stage‐3 and 42.3% thinning with ?21dB PSLL for stage‐4) than its original counterpart in terms of reduced element count and PSLL. Numerical results for obtaining optimized array performance exploit both DE as well as PSO. A comparative study on the performance is also presented. As a whole, Haferman carpet is seen to be more effective approach than Sierpinski carpet in fractal antenna paradigm. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:719–729, 2015.     

Broadband T‐bar fed slot antenna array with stable horizontally polarized omnidirectional radiation

A broadband horizontally polarized omnidirectional antenna array is proposed, which consists of a circular array of four identical broadband T‐bar fed cavity‐backed slot antenna elements and a 1‐to‐4 power divider. The proposed omnidirectional antenna array has a compact diameter of only 0.44λ₀, a broad bandwidth of 75.9% (450‐1000 MHz) and a favorable omnidirectional radiation pattern in the azimuth plane with a gain variation below 3 dB in the operating band. Moreover, the cavity‐backed structure makes the proposed antenna array hardly affected by metal environment and the all metal construction allows for high‐power applications, and the reserved cable channel behind the cavities of the antenna elements ensures the extensionality and stability of the proposed array when longitudinal array expansion is needed. Design procedures of the proposed antenna array have been described in detail, simulations and measurements of the proposed antenna array have also been carried out to validate its performance in this article.     

Development of an Enhanced Ant Lion Optimization Algorithm and its Application in Antenna Array Synthesis

In order to design a highly effective communication system, antenna plays a vital role and antenna array adds to the performances. And to achieve such a goal, the crucial challenge is to determine the optimum spacing between the elements and their excitations. In order to address this issue a novel optimization technique named as enhanced ant lion optimization (e-ALO) algorithm has been developed by modifying the basic Ant lion optimization algorithm. Further, to validate the efficacy of the proposed algorithm, few benchmark functions have been successfully tested and significant improvement is obtained in comparison to other reported optimization approaches. The proposed scheme is applied to antenna array synthesis problem to optimize the inter-element spacing and excitation of the elements for different antenna geometries, with an objective to minimize the sidelobe levels while keeping other constraints within boundary limits. The encouraging results obtained from the study have emphatically placed the proposed e-ALO algorithm in the optimization arena as a dominant player.     

Synthesis of sparse planar antenna arrays with multiple constraints

Synthesis of symmetrical sparse planar antenna arrays is introduced in this paper. In order to reduce the peak sidelobe level of the radiation pattern, the element positions of the arrays are optimized by invasive weed optimization with complex boundary conditions. The proposed algorithm changes a two‐dimensional optimization problem into a linear problem, which will reduce the complexity of the optimization procedure. The optimization method can constrain the size of the array aperture, the element number of the array, and the minimum spacing of the adjacent elements simultaneously. The simulation results show the robustness and effectiveness of the proposed method.     

Synthesis of linear antenna array using flower pollination algorithm

Linear antenna array (LAA) design is a classical electromagnetic problem. It has been extensively dealt by number of researchers in the past, and different optimization algorithms have been applied for the synthesis of LAA. This paper presents a relatively new optimization technique, namely flower pollination algorithm (FPA) for the design of LAA for reducing the maximum side lobe level (SLL) and null control. The desired antenna is achieved by controlling only amplitudes or positions of the array elements. FPA is a novel meta-heuristic optimization method based on the process of pollination of flowers. The effectiveness and capability of FPA have been proved by taking difficult instances of antenna array design with single and multiple objectives. It is found that FPA is able to provide SLL reduction and steering the nulls in the undesired interference directions. Numerical results of FPA are also compared with the available results in the literature of state-of-the-art algorithms like genetic algorithm, particle swarm optimization, cuckoo search, tabu search, biogeography based optimization (BBO) and others which also proves the better performance of the proposed method. Moreover, FPA is more consistent in giving optimum results as compared to BBO method reported recently in the literature.

     

An optimal circular antenna array design considering mutual coupling using heuristic approaches

This article shows the design of a non‐uniformly excited single ring circular antenna array (CAA) for the synthesis of optimal far‐field radiation characteristics. A recently proposed meta‐heuristic based optimization algorithm called gray wolf optimization (GWO) and state‐of‐the‐art swarm intelligence based evolutionary optimization technique known as particle swarm optimization with a distribution based update mechanism (PSOd) are individually applied to determine the optimum set of current excitation amplitude weights and the inter‐element spacing among the array elements to reduce the side lobe level and 3‐dB beamwidth considering the mutual coupling. The results obtained by employing PSOd and GWO are compared to those of the uniform radiation pattern and the recently published results of state‐of‐the‐art literature having equal sets of elements to show the superiority of employed approaches. Three different design examples of 8, 10, and 12 elements CAA are reported in this article to study the performances of PSOd and GWO algorithm‐based results over the results of other recently reported literature.     

Synthesis of thinned concentric circular antenna arrays using teaching‐learning‐based optimization

In this article, the design of thinned concentric circular antenna arrays (CCAAs) of isotropic radiators with optimum side lobe level (SLL) reduction is studied. The newly proposed global evolutionary optimization method; namely, the teaching‐learning‐based optimization (TLBO) is used to determine an optimum set of turned ON elements of thinned CCAAs that provides a radiation pattern with optimum SLL reduction. The TLBO represents a new algorithm for optimization problems in electromagnetics and antennas. It is shown that the TLBO provides results that are somewhat better than those obtained using other evolutionary algorithms, like the firefly algorithm and biogeography based optimization. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:443–450, 2014.     

Modeling of mutual coupling of arbitrary order in coupled circuits and array antennas

This article presents a fundamental strategy for accurately modeling the mutual coupling of arbitrary order in any large‐scale electromagnetic structures and high‐density integrated chips such as antenna array elements and coupled circuit elements. The proposed method starts from the modeling of the first‐order mutual coupling, and it consists of two main steps. First of all, an equivalent circuit model describing low‐order mutual coupling (adjacent coupling) is characterized and established, of which each parametric value is accurately extracted by making use of a numerical calibration technique. Then, the circuit model for high‐order mutual coupling (crossover or crosstalk coupling) is generated from the lower order models, and it can further be used for the modeling of mutual coupling of any higher order. The accuracy and efficiency of the proposed method are demonstrated by three different kinds of structure including a linear phased array antenna, a finite periodic electromagnetic structure, and a planar low‐pass filter. This novel approach represents an easy, fast, and effective characterization of arbitrary‐order mutual coupling. It can find applications in the modeling of mutual coupling between any circuit elements and building blocks such as antennas, resonators, and even small discontinuities, and it promises to be helpful for the analysis and iterative design of microwave circuits and antenna arrays. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Slot antenna array for fifth generation metal frame mobile phone applications

An eight‐element antenna array based on open/closed slot modes that can cover the 3.5 GHz band (3400‐3600 MHz) is proposed and studied. There are two kinds of antenna elements with the slot sizes of 10.8 × 1 mm² and 28.8 × 1 mm² for open and closed slot modes, respectively. Both the two kinds of antenna elements are realized with the help of the metal frames with the height of 7 mm at the two long sides of the ground. The proposed antenna array is suitable for 5G metal frame mobile phone applications. A prototype is fabricated and measured. The measured results show that all the eight antenna elements can cover the band of 3400‐3600 MHz and the isolations are bigger than 13 dB, the measured efficiencies all are bigger than 42% and the measured envelope correlation coefficients are lower than 0.15.     

A wideband circularly polarized antenna array with sequential rotation feed

A novel wideband circularly polarized (CP) antenna array is designed, which consists of a horizontally placed wideband phase shifting feed network and four vertically placed linearly polarized dipole antenna elements, and the circular polarization is realized based on sequential rotation feeding technology. By placing two parasitic strips and two grounding strips on the top and side of each T‐shaped dipole antenna element, the impedance bandwidth and circular polarization performance of the antenna can be further improved. The simulation results show that the 10‐dB impedance bandwidth of the antenna is 93% (1.56‐4.27 GHz) and the 3‐dB AR bandwidth is 80.7% (1.7‐4.0 GHz). The measured results are in good agreement with the simulation results. Due to the use of orthogonally placed wideband feed network and wideband array elements, the proposed antenna array has a wider circular polarization bandwidth than the similar antenna arrays reported.     

High gain substrate integrated waveguide beam scanning antenna with sub‐array elements

A method to enhance the gain of substrate integrated waveguide (SIW) beam scanning antenna is proposed in this article. 2 × 2 SIW cavity‐backed sub‐arrays are employed in array design. The antenna is constructed on two layers. The top layer places four SIW cavity‐backed sub‐arrays as radiating elements and the bottom layer is an SIW transmission line to feed the sub‐arrays. Beam scanning feature can be obtained due to the frequency dispersion. Moreover, through separating radiators to the other layer and using 2 × 2 SIW cavity‐backed sub‐arrays as radiating parts, the antenna gain is improved significantly. For a linear array, 4.1 to 6.8 dB gain enhancement is achieved compared to a conventional SIW beam scanning antenna with the same length. Then, the linear array is expanded to form a planar array for further gain improvement. A 64‐element planar beam scanning array is designed, fabricated, and tested. Experimental results show that the proposed planar array has a bandwidth from 18.5 GHz to 21. 5 GHz with beam scanning angle from ?5° to 11.5° and gain in the range of 20.5 to 21.8 dBi. The proposed high gain beam scanning antennas have potential applications in radar detection and imaging.     

Antipodal tapered slot antenna array using broadband decoupling structure for mutual coupling reduction

In this article, an effective method to reduce the mutual coupling between the antipodal tapered slot antenna (ATSA) array is proposed. This method is mainly implemented by loading a set of decoupling structures (DS) perpendicular to the dielectric substrate between two antenna elements. The proposed DS can provide transmission forbidden band which can effectively prevent leaked electromagnetic waves. DS can operate in most frequency bands within 4 to 17.5 GHz. It can enhance about 23 dB isolation between the ATSA array without affecting bandwidth and radiation characteristics. The proposed ATSA arrays are fabricated and tested. The measured results can verify its excellent properties. The proposed broadband decoupling method is a suitable candidate for restrain mutual coupling of ultra‐wideband planar end‐fire antennas. This design sheds new light on broadband decoupling.     

A polarization‐reconfigurable array design based on mode combination technique

This article reports a novel polarization‐reconfigurable antenna array using the technique of mode combination (MC). It can electronically alter its polarization states between left‐hand circular polarization mode, right‐hand circular polarization mode, and linear polarization (LP) mode. The antenna array consists of 2 × 2 microstrip antenna elements with one L‐slot on each square patch and two PIN diodes located in the slot region. Instead of degenerating circular polarization (CP) and LP modes by exciting different radiation parts of the antenna element, the LP one is combined by orthogonal CP modes generated by adjacent elements of the proposed antenna array. To verify the concept, a prototype is manufactured and tested. Experimental results show that the proposed antenna has an overlapped ?10 dB impedance bandwidth of around 11.2% for both CP modes and the LP one. The realized maximum gains are around 7.5 dB for the CP modes and 5.6 dB for the LP mode, which are satisfactory for wireless local area network in wireless communication systems.     

A linear antenna array failure correction using improved bat algorithm

The failure of antenna array elements causes disturbance in the sidelobe power level. In this article, an improved flexible approach that use bat algorithm is proposed and applied to solve the problem of antenna array failure by controlling only the amplitude excitation of array elements. An adaptive inertia weight approach is applied to the standard bat algorithm to improve the quality of the solution and the speed of convergence. The effectiveness of the proposed improved bat algorithm (IBA) is verified on different standard test functions. Numerical examples of element failure correction are presented to show the capability of this flexible approach in antenna array failure correction.     

Decoupling antenna array with X‐shaped strip

Manipulating mutual coupling between antenna array elements is always a critical essential in designing phased arrays. In this article, an X‐shaped strip is applied to decouple a five‐element E‐plane microstrip antenna array, whose adjacent elements' center‐to‐center spacing is only 0.45 λ₀. Simulation and measurement results reveal that the proposed array employing the loaded structure exhibits excellent decoupling capability, as in comparison to the reference array, impedance of every port is well matched, mutual coupling between both adjacent elements and nonadjacent ones is efficiently reduced and radiation patterns of every individual patch are markedly corrected. Besides, when beam scanning is performed, the proposed array is equipped with higher gain and lower SLL. The X‐shaped strip predicts a promising application in phased array and a large‐scale array.     

On techniques for optimal noise matching of a class of multimode antenna

This article investigates techniques to design noise‐matching networks for a class of multimodal antennas, specifically, the so‐called quad‐mode antenna. Such an antenna utilizes weighted combinations of four very dissimilar radiation patterns, and different modal input impedances, which vary across scan angle. The matching problem is therefore quite different from that of a classical array, where antenna elements are normally assumed to be similar. In addition to the standard techniques, a new, recursively averaged active impedance, is proposed and applied, as well one using a noise‐active impedance, and two optimization approaches. It is shown for the first time that the quad‐mode antenna displays excellent noise properties, with the simplest technique, namely that of matching to the self‐impedances, producing noise performances across all scan angles which are almost as good as the best solution found by all the techniques.     

Development of phased array antenna by controlling the filling factor of periodic structure

A phased array antenna is realized by utilizing the variation of filling factor (FF) of electromagnetic bandgap (EBG) structures. The variation takes place under the feed line of a 4‐element array that gives the change in relative phase shift. The phase shift achieved from different combinations of EBGS lying under the feed lines is used in personal computer aided antenna design software, PCAAD 4.0, to see the beam steering capacity. Then the same feed lines are connected with four microstrip patches to yield a 4‐elements phased array antenna. The 4‐elements phased array antenna is simulated in electromagnetic (EM) software Zeland IE3D. Finally, the design is fabricated with the help of milling machine that takes the help of ISOPRO and QUICKCAM software. It can be seen that the beam steering angle increases with the increase of FFs. Thus a novel FF of EBGS based phased array antenna is developed. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

Spectral efficiency enhancement using an antenna‐based orthogonal frequency division multiaccess technique

An approach to enhance antenna spectral efficiency is proposed based on combining spacetime electromagnetic (EM) models of Tx/Rx antennas with orthogonal frequency division multiaccess (OFDM), leading to the EM‐OFDM, a technology capable of removing intersymbol interference (ISI) in high‐data rate communication links caused by the EM‐induced distortion antenna effects. The proposed approach differs from traditional OFDM in wireless communication in several aspects. First, the technique suggests a new decoupling approach by treating each given antenna transreceive device pair as a “stand‐alone channel” with its own distortion mechanisms considered separately from the propagation channel. Moreover, the deterministic distortion caused by the nonflat pure antenna EM filtration effects is exploited to carefully design a specialized OFDM transmission techniques based on the antenna parameters, not the multipath fading channels often invoked in conventional uses of OFDM methods. (The EM‐OFDM, however, can be combined with a traditional OFDM later if fading channels are present.) In this manner, a more efficient implementation of the wireless link equalization strategy may be enacted since the EM antenna origin of ISI is very different from the traditional propagation channel one. As a proof of concept, the proposed EM‐OFDM method is implemented for a single‐input‐single‐output link comprised of half‐wavelength linear wire antennas. A careful use of finite difference time‐domain to provide EM data allowed the construction of 64 decoupled “pure antenna OFDM subchannels.” Simulation results suggests that the antenna‐based OFDM system is capable of completely neutralizing all ISI effects caused by the limited antenna matching bandwidth of the transreceive wires, therefore, supporting considerably higher data rates with low symbol error rate (SER). A concrete evaluation of the SER using quadrature phase‐shift keying (QPSK) digital carrier modulation resulted in an increase of the effective antenna digital communication spectral efficiency by ratios up to 300%. Moreover, the EM‐OFDM error rate was found to be close to the ideal QPSK level or the maximum possible theoretical limit. Thus, combining detailed EM knowledge with standard signal processing methods can lead to considerable improvement in system design without modifying the antenna physical layout. The proposed approach is expected to play a role in the forthcoming 5G/6G and millimetre wave technology systems currently under development where there is a trend toward integration of EM and digital signal processing at the physical layer level.     

Near optimal conformal antenna array structure for direction‐of‐arrival estimation

This article determines the near optimal conformal antenna array structure for direction‐of‐arrival (DOA) estimation through a comprehensive study on the planar and usual conformal antenna arrays including the cylindrical and hemispherical by using the directive antenna elements in all designs. To model the hemispherical structure, an improved multi‐face antenna array with three different tilts is proposed and compared with previous works in order to investigate the tilt effect and obtain the conclusive results. The Cramer‐Rao lower bound, multiple signal classification, and root‐mean‐square error algorithms are utilized to evaluate the estimation accuracy of all conformal structures. Finally, by comparing the estimation precision of all conformal structures it is shown that the purposed multi‐face structure as the hemispherical model has a better performance than other conformal structures in terms of the maximum angular coverage of the spatial resource. Moreover, the proposed study method in this article fully examines the impacts of the different conformal antennas geometric structure on the DOA estimation performance by involving the directive antennas radiation patterns.     

Fast simulation‐driven optimization of planar microstrip antenna arrays using surrogate superposition models

A technique for simulation‐driven design of excitation tapers for planar antenna arrays is presented. Our methodology exploits antenna array models constructed as a superposition of simulated radiation and reflection responses of the array under design, with only one radiator active at a time. Low computational costs of these models are ensured by using iteratively corrected electromagnetic‐simulation data computed with coarse meshes. Our technique allows for simultaneous control of the radiation pattern and the reflection coefficients of the array. Numerical efficiency as well as scalability of the technique is demonstrated using the design examples of various sizes and topologies, including a sixteen element and hundred element microstrip patch antenna arrays of the Cartesian lattice and a hundred element microstrip antenna array of the hexagonal lattice. The proposed technique is versatile as it also can be applied for simulation‐based optimization of antenna arrays comprising other types of individually fed elements, e.g., wires, strips, or dielectric resonator antennas. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:371–381, 2015.