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In this article, a novel dual-polarized embroidered textile antenna array with an omnidirectional radiation pattern is proposed for both on- and off-body wearable applications. The flexible antenna is composed of a group of circularly oriented dual-polarized patch antennas excited with uniform amplitude and phase. The antenna array can be wrapped around a cylinder, such as an arm or a leg, for realizing a quasi-omnidirectional radiation pattern in the azimuthal plane, which is highly desirable in both on-body and off-body wearable applications. The operating principles and design consideration for how to achieve the omnidirectional radiation and how to avoid radiation nulls are investigated in detail. Moreover, these analytical studies are verified through the experimental results. In addition, a dual orthogonal polarization capability is employed to improve the link reliability. Due to the high front-to-back ratio (FBR) exhibited by each patch antenna element, the proposed omnidirectional antenna array also features a low specific absorption rate (SAR) and high efficiency, which are extremely important for wearable applications. As a proof-of-concept, an antenna array prototype operating at 5.8 GHz is designed, fabricated, and tested. The measured results agree reasonably well with the simulations in terms of S-parameters, polarization isolation, and radiation patterns, demonstrating that the proposed antenna array is ideally suited for potential wearable applications. [ABSTRACT FROM AUTHOR]

Metasurfaces with independently tunable anisotropic dispersion characteristics have been designed to significantly improve the radiation efficiency of a short backfire antenna (SBFA) when placed within the antenna cavity walls. This advanced SBFA (A-SBFA) features a hexagonal aperture, which typically results in much lower aperture efficiency and increased cross polarization. However, the addition of metasurfaces leads to a higher aperture efficiency than is achievable with a conventional circular SBFA. Through careful design and optimization of the metasurface dispersion, the A-SBFA achieves high aperture efficiency across two discrete frequency bands while maintaining a relatively low height and weight. A detailed design and optimization methodology is presented here, along with the simulation studies that explore the design space and provide insight into how the antenna performance is affected as the metasurface parameters are adjusted. The A-SBFA is shown to be a promising candidate for future satellite-based antenna arrays due to its high aperture efficiency, hexagonal cavity, low weight, and low profile. [ABSTRACT FROM AUTHOR]

A novel self-diplexing aperture-shared dual-band dual-sense circularly polarized (CP) antenna array is proposed for transmitting/receiving (Tx/Rx) applications in X-band satellite communication systems. The antenna is capable of receiving the left-handed CP (LHCP) signals in the low band while transmitting the right-handed CP (RHCP) signals in the high band. First, a dual-port cavity-fed linearly polarized (LP) patch antenna with high isolation is developed as the element of the array. The element is composed of a slotted patch, a U-slot loaded substrate integrated cavity (SIC), and two groups of split-ring resonators (SRRs). The LHCP and RHCP operations are achieved by employing two sequentially rotated feeding networks which are isolated by a ground plane. To reduce the mutual coupling between the radiators, narrow slots are etched out in the center of the patches. Importantly, the sharing of patches at different bands (i.e., common aperture) enables a compact footprint to be achieved for the array, which is beneficial for suppressing undesirable grating lobes due to the reduced interelement spacing. The measured results of a fabricated prototype agree well with the simulations, showing an impedance bandwidth of 7.2–7.75 GHz (7.85–8.4 GHz), 3 dB axial ratio (AR) bandwidth of 7.4–7.7 GHz (7.95–8.32 GHz), and gain of 14 dBic (14.2 dBic) at the low band (high band). The channel isolation is over 27 dB and the sidelobe levels are below −15 dB in both bands. The demonstrated low-profile dual-band, dual-sense CP antenna array can be a good candidate for satellite communication. [ABSTRACT FROM AUTHOR]

Multiobjective optimization (MOO) provides the designer with a set of solutions that show potential tradeoffs between multiple conflicting objectives-e.g., performance and cost. Despite its utility, MOO is not as popular in electromagnetics (EMs) and optics as it is in other fields, such as economics, finance, and mechanical and chemical engineering. This article will provide a tutorial and introduction for electrical engineers interested in using a MOO algorithm. [ABSTRACT FROM AUTHOR]

Recently, a robust and versatile multiobjective lazy ant colony optimization technique was introduced for inverse design of 3-D frequency selective structures (FSSs) with remarkable polarization independent filtering performance for incidence angles up to 80°. However, fabricating and characterizing these elements present many challenges that have yet to be addressed. For example, conventional free-space measurement techniques require intractably large arrays to uniformly illuminate the sample and mitigate edge diffraction at extreme incidence angles. To mitigate these effects, a broadband focused beam measurement technique is proposed to characterize a finite $24 \times 48$ element 3-D FSS array optimized for C-band operation. Elements are fabricated using PolyJet 3-D printing, metallized, and encapsulated in a Sylgard-527 substrate over a polymethylmethacrylate lattice resulting in a low-loss, low-cost, low-profile, and lightweight array that is suitable for conformal surfaces and can be easily repaired. A comparison of simulated and measured results is presented, and a discussion of the implications of the array and measurement system is offered. The fully fabricated 3-D FSS array achieves a 6.25% −10 dB rejection band and 8.26% 3 dB passband at 5.6 and 7.75 GHz, respectively, for both TE and TM polarizations and incidence angles up to 72°. [ABSTRACT FROM AUTHOR]

Recently, the covariance matrix adaption evolutionary strategy (CMA-ES) has received attention for outperforming conventional global optimization techniques such as the genetic algorithm (GA) or particle swarm optimization (PSO), often used in electromagnetic designs. Here, CMA-ES is first applied to the design of ultra-wideband aperiodic arrays using realistic spiral radiating elements. To improve the axial ratio of the array, optimization was extended to incorporate a mechanical rotation of each spiral element. This novel strategy of optimizing both the location and rotation of each element provides noticeable improvement in both the axial ratio and sidelobe level performance. [ABSTRACT FROM PUBLISHER]

Micro-UAV swarm-based antenna arrays provide a novel solution for high-risk radar imaging applications. These apertures lack a single point of failure by distributing their resources and sensors across multiple platforms. However, turbulence and positional errors provide a challenging operational environment when it comes to the implementation of these systems. Turbulence can limit the aperture's ability to coherently resolve a target and cause aircrafts to collide in midair if the formation is too tightly packed with closely spaced elements. This paper introduces several techniques that can reduce the effects of turbulence on the system. First, a phase compensation algorithm is presented that can eliminate the effects of turbulence on the main beam of the array. In addition, sparse antenna apertures can be used to create flight formations that reduce the probability of midair collisions. Traditional periodic apertures are insufficient because these arrays display grating lobes at wide interelement spacings. Therefore, two aperiodic array optimization methodologies are discussed that produce sparse array configurations suitable for micro-UAV formations. These sparse arrays exhibit low peak side-lobe levels without the presence of grating lobes over wide interelement spacings. By combining phase compensation with optimized sparse aircraft formations, one can achieve high radiation pattern resolution in a micro-UAV based radar imaging application. [ABSTRACT FROM PUBLISHER]

A multi-objective Pareto genetic algorithm design methodology is applied to thinned planar arrays to simultaneously minimize peak side-lobe levels and target an elliptical mainbeam with specific minimum and maximum half-power beamwidths. This new radiation pattern synthesis technique for thinned planar arrays provides antenna engineers with a set of tradeoffs between low side-lobe levels and close adherence to mainbeam design objectives (i.e., the specified half-power beamwidths corresponding to the major and minor axes of an elliptical mainbeam). One Pareto optimization example is presented for a thinned low side-lobe planar array with a desired minimum and maximum beamwidth of 8.4^\circ and 12^\circ respectively. Two designs from the Pareto front are discussed, one with a -20.92~dB side-lobe level and beamwidths between 11.5^\circ and 7.5^\circ and a second with a -18.97~dB side-lobe level with beamwidths between 12^\circ and 7.93^\circ. [ABSTRACT FROM AUTHOR]

The Peano-Gosper space-filling curve provides an excellent framework for designing planar antenna array distributions with modular architectures and suppressed sidelobes over a relatively wide bandwidth. The curve consists of a self-avoiding path that intersects a triangular lattice and its construction is based on the iterative application of a generating curve. There exist a number of other recently discovered curves, coined generalized Gosper curves, that possess properties similar to those of the Peano-Gosper curve but are based on larger and more complex generating curves. In this paper these generalized curves will be examined as the framework for antenna array layouts. It will be shown that arrays based on these curves have a number of excellent characteristics while offering modular array configurations and sizes that are not inherent to Peano-Gosper arrays. Moreover, when combined with a simple recursive-perturbation technique, the element distributions of these arrays can be efficiently adjusted to generate designs with bandwidths that far exceed that of standard periodic- and triangular-lattice arrays. The efficacy of this technique will be demonstrated through design examples, including one that has more than a 10:1 bandwidth. Full-wave simulations of a wideband patch array will also be used to investigate the effects of mutual coupling on these array distributions. [ABSTRACT FROM AUTHOR]

There is considerable interest in interleaving multiple phased array antennas into a single common aperture system. Current phased array antenna technology is limited to narrowband operation, leading to the appearance of grating lobes and strong mutual coupling effects when they are incorporated into the design of a common aperture system. To overcome this obstacle, a new class of arrays, called polyfractal arrays, has been introduced that possess natural wideband properties well suited for large-scale genetic algorithm optimizations. These arrays also possess recursive beamforming properties and an autopolyploidy-based chromosome expansion that can dramatically accelerate the convergence of a genetic algorithm. In addition, a robust Pareto optimization can be applied to reduce the peak sidelobe levels at several frequencies throughout the intended operating band, leading to ultrawideband antenna array designs. Because of their lack of grating lobes, these polyfractal arrays are ideal building blocks for interleaved antenna array systems. This paper develops these concepts, first creating ultrawideband array designs based on polyfractal geometries and then interleaving these designs into a common aperture system. Several examples of interleaved systems are discussed, with one two-array system possessing a peak sidelobe level of nearly -18 dB with no grating lobes over a 20:1 bandwidth with either of the component array mainbeams steered independently up to 60° from broadside. [ABSTRACT FROM AUTHOR]

Antenna arrays based on aperiodic tilings have been shown to exhibit low sidelobe levels and modest bandwidths over which grating lobes are suppressed. In addition, compared to conventional periodic arrays, these arrays are naturally thinned (i.e., mean interelement spacing is greater than λ/2). The generation of these arrays involves placing array elements at the locations of the vertices of an aperiodic tiling. To obtain a realizable design, the entire array is then scaled and truncated to achieve a desired minimum element spacing and aperture size. This paper demonstrates that it is possible to greatly extend the bandwidth of these arrays by incorporating a simple perturbation scheme into the basic array generation process. The implementation of this perturbation scheme is straightforward and it lends itself well to being combined with an optimization technique such as the genetic algorithm. It is successfully used to generate arrays that have large bandwidths (peak sidelobe level ≤ -10 dB with no grating lobes) of up to a minimum element spacing of 5λ. Moreover, the flexibility of this technique will be further demonstrated by introducing a slight variation of the basic scheme that is capable of generating arrays with extremely wide bandwidths. An example will be presented for an array design that has a bandwidth corresponding to a minimum element spacing of up to 11λ. [ABSTRACT FROM AUTHOR]

The application of global optimization techniques, such as genetic algorithms, to antenna array layouts can provide versatile design methodologies for highly directive, thinned, frequency agile, and shaped-beam antenna systems. However, these methodologies have their limitations when applied to more demanding design scenarios. Global optimizations are not well equipped to handle the large number of parameters used to describe large-N antenna arrays. To overcome this difficulty, a new class of arrays was recently introduced called polyfractal arrays that possess properties well suited for the optimization of large-N arrays. Polyfractal arrays are uniformly excited with an underlying self-similar geometrical structure that leads to aperiodic element layouts. This paper expands on polyfractal array design methodologies by applying a robust Pareto optimization technique with the goal of reducing the peak sidelobe levels at several frequencies specified over a wide bandwidth. A recursive beamforming algorithm and an autopolyploidy based mutation native to polyfractal geometries are used to dramatically accelerate the genetic algorithm optimization process. This paper also demonstrates that the properties of polyfractal arrays can be exploited to create designs that possess no grating lobes and relatively low sidelobe levels over ultrawide bandwidths. The best example discussed in this paper maintains a -15.97 dB peak sidelobe level with no grating lobes from a 0.5λ, to more than a 20λ minimum spacing between elements, which corresponds to at least a 40:1 bandwidth for the array. [ABSTRACT FROM AUTHOR]

There has been considerable recent interest in techniques for the optimization of large-N antenna arrays. Unfortunately, the successful development of such techniques has been hindered by the large number of independent parameters that must be optimized and the complexity of the calculations needed for the electromagnetic evaluation of large-N arrays. One promising new design methodology for large-N arrays which has recently been introduced is based on properties of a subset of fractal-random arrays called polyfractal arrays. Polyfractal arrays have many embedded self-similar structures, thereby allowing very large and seemingly complex array layouts to be described with only a small set of independent parameters. In addition, by effectively utilizing the self-similarity of polyfractal arrays, a considerable reduction can be achieved in the amount of time required to evaluate the radiation patterns of large-N arrays. This paper introduces a type of nature-based design process that applies a specially formulated genetic algorithm (GA) technique to evolve optimal polyfractal array layouts. The most unique aspect of this optimization technique is a new autopolyploidy-based chromosome expansion that maximizes the efficiency of the GAs. Simple polyfractal geometries are used in the initial stage or first epoch of the optimization because the number of independent parameters is small and the computation times are relatively fast. After the optimization converges for the first epoch, more complicated descriptions of these polyfractal arrays are introduced to provide additional independent parameters for the optimizer as it progresses through later epochs of evolution. This process has been shown to be very effective in creating optimized large-N arrays, the largest example considered here being a 1616-element linear array with a -24.30-dB sidelobe level and a 0.056deg half-power beamwidth [ABSTRACT FROM PUBLISHER]

For conformal phased arrays, generally the excitation amplitude of the array elements must be adjusted in order to maintain low sidelobes as the array is scanned. While the desired phase weights for maximum gain are deterministically set by the array geometry and scan angle, the representation of optimum low sidelobe amplitude weights remains an open problem. Following up on prior work using the efficiency-constrained optimization of a modified Bernstein polynomial for low sidelobe conformal array synthesis, a Bézier surface is shown to provide a good representation of the optimized amplitude weights with a reduced number of parameters, while demonstrating ϵ-constraint multi-objective optimization of conformal aperture efficiency versus sidelobe level. These results are extended to include a Bézier volume representation for the multiobjective optimization of conformal aperture efficiency versus both sidelobe level and scan angle. [ABSTRACT FROM AUTHOR]

As various enabling technologies advance, conformal phased arrays are finding more numerous applications. Because a conformal array is curved, new far field pattern behaviors emerge and many of the traditional linear and planar phased array synthesis methods are not valid. This paper starts by reviewing the equations for the far field of a curved phased array, and provides a generalized definition of aperture efficiency appropriate for con- formal arrays. A modified Bernstein polynomial, defined with just five parameters, is introduced which provides a flexible method to specify a variety of smooth unimodal amplitude distributions that are shown to give good sidelobe levels and aperture efficiencies. By using particle swarm optimization of the modified Bernstein polynomial parameters constrained to provide a specified aperture efficiency, a family of aperture distributions and corresponding far field patterns is produced that allows aperture efficiency to be traded for sidelobe level. [ABSTRACT FROM AUTHOR]

Genetic algorithms are commonly used to solve many optimization and synthesis problems. An important issue facing the user is the selection of genetic algorithm parameters, such as mutation rate, mutation range, and number of crossovers. This paper demonstrates a real-valued genetic algorithm that simultaneously adapts several such parameters during the optimization process. This adaptive algorithm is shown to outperform its static counterparts when used to synthesize the phased array weights to satisfy specified far-field sidelobe constraints, and can perform amplitude-only, phase-only, and complex weight synthesis. When compared to conventional static parameter implementations, computation time is saved in two ways: 1) The algorithm converges faster and 2) the need to tune parameters by hand (generally done by repeatedly running the code with different parameter choices) is greatly reduced. By requiring less iteration to solve a given problem, this approach may benefit electromagnetic optimization problems with expensive cost functions, since genetic algorithms generally require many function evaluations to converge. The adaptive process also provides insight into the qualitative importance of parameters, and dynamically adjusting the mutation range is found to be especially beneficial. [ABSTRACT FROM AUTHOR]

In this paper, a new class of antenna arrays are introduced, which we call fractile arrays. A fractile array is defined as any array with a fractal boundary contour that tiles the plane without gaps or overlaps. It will be shown that the unique geometrical features of fractiles may be exploited in order to make available a family of deterministic arrays that offer several highly desirable performance advantages over their conventional pen odic planar array counterparts. Most notably, fractile arrays have no grating lobes even when the minimum spacing between elements is increased to at least one-wavelength. This has led to the development of a new design methodology for modular broadband low-sidelobe arrays that is based on fractal tilings. Several examples of fractile arrays will he considered including Peano-Gosper, terdragon, 6-terdragon, and fudgeflake arrays. Efficient iterative procedures for calculating the radiation patterns of these fractile arrays to arbitrary stage of growth P are also introduced in this paper. [ABSTRACT FROM AUTHOR]

This paper investigates the radiation characteristics of a new type of array that is based on the family of space-filling and self-avoiding fractals known as Peano-Gosper curves. The elements of the fractal array are uniformly distributed along a Peano-Gosper curve, which leads to a planar array configuration with parallelogram cells that is bounded by a closed Koch curve. These unique properties are exploited in order to develop a design methodology for deterministic arrays that have no grating lobes even when the minimum spacing between elements is increased to at least one wavelength. This leads to a class of arrays that are relatively broad-band when compared to more conventional periodic planar arrays with square or rectangular cells and regular boundary contours. An efficient iterative procedure for calculating the radiation patterns of these Peano-Gosper fractal arrays to arbitrary stage of growth P is also introduced in this paper. [ABSTRACT FROM AUTHOR]

A novel method for designing reconfigurable multiband linear and planar antenna arrays is presented in this paper. The technique is based on a generalized Fourier series synthesis approach that exploits the self-similarity of a specified fractal radiation pattern in order to achieve the desired multiband performance. The fractal radiation patterns are composed of scaled and shifted copies of an appropriately chosen generating window function that exhibits low sidelobe levels and rapid spectral rolloffs in the transform domain. A newly developed thinning algorithm will be presented which may be employed to considerably reduce both the overall physical size as well as the total number of elements in a synthesized multiband array. Finally, a band-switching scheme is introduced that is well-suited for implementation in the form of a reconfigurable common aperture array. [ABSTRACT FROM AUTHOR]

A domain-decomposition/reciprocity procedure is presented which allows the radiation patterns of microstrip patch antennas mounted on arbitrarily-shaped three-dimensional perfectly electric conducting (PEC) platforms to be computed accurately as well as efficiently. The utility of this technique is demonstrated by considering an example consisting of a nine-element conformal array of microstrip patch antennas mounted axially along a finite-length PEC circular cylinder. It is shown that the elements close to the ends of the cylinder have significantly different patterns than those close to the center of the cylinder. The results from this example suggest that the common practice where all the individual element patterns are assumed identical is not always valid and, in fact, can lead to significant performance degradation in the design of conformal phased arrays. This observation is supported by the fact that an attempt to steer the main beam of the nine-element conformal array to an angle θ[sub 0] = 60° using a standard uniform progressive phase shifting technique proves unsuccessful. Next a genetic algorithm (GA) synthesis procedure is introduced that is capable of determining the optimal set of element excitation phases required to yield a desired or specified far-field radiation pattern. The results of this GA phase-only optimization are shown to yield the desired main beam steered to the correct angle for this nine-element linear array mounted on a circularly cylindrical platform. The GA radiation pattern synthesis procedure introduced appears to be a highly effective means of correcting for platform effects on the individual element patterns of a conformal phased array. [ABSTRACT FROM AUTHOR]

Provides updates in the field of fractal antenna engineering. Analysis of the design of fractal antenna elements; Application of fractal components to the design of antenna arrays; Highlights of related works in fractal frequency-selective surfaces.

The scan volume of a thinned periodic linear phased array is proportional to the spacing between array elements. As the spacing between elements increases beyond a half wavelength, the scan range of the array will be significantly reduced due to the appearance of grating lobes. This paper will investigate a method of creating thinned aperiodic linear phased arrays through the application of genetic algorithms that will suppress the grating lobes with increased steering angles. In addition, the genetic algorithm will place restrictions on the driving-point impedance of each elemerit so that they are well behaved during scanning. A genetic algorithm approach will also be introduced for the purpose of evolving an optimal set of matching networks. Finally, an efficient technique for evaluating the directivity of an aperiodic array of half-wave dipoles will he developed for use in conjunction with genetic algorithms. [ABSTRACT FROM AUTHOR]

This paper introduces a powerful technique that utilizes a hybrid Particle-Swarm Optimization (PSO) method for the design optimization of aperiodic linear phased arrays of tightly packed miniature meander-line dipole elements. Miniaturization is achieved by first introducing a fixed grid of reduced length, and then employing a hybrid PSO to determine the optimum meander-wire shape on the grid and the optimal element spacing. The purpose was to achieve comparable performance in terms of voltage standing-wave ratio (VSWR) and sidelobe levels during scanning to conventional full-size periodic phased arrays of linear half-wave dipoles. This design technique is applicable in cases where the desire for aperture miniaturization takes precedence over the reduction in gain that comes as a consequence. As one of the design criteria, the same number of antenna elements was maintained and tightly packed into a smaller aperture area. This allowed the antenna elements to be driven by lower-power transmitting modules for a given effective radiated power (ERP), compared to a thinned array with the same aperture size. This method also provides flexibility in controlling the self impedance of individual elements and the mutual coupling among array elements. It is hence capable of evolving compact array configurations with meander-line dipole elements that have well-behaved driving-point impedances and low sidelobe levels over a prescribed scan range. In order to overcome the optimization difficulty of arrays with a large number of antenna elements, orthogonal design with quantization (OD/Q) was employed for this mixed-valued optimization problem to generate relatively fit particles at the initialization stage. Several design examples were considered with parallel or planar grids, and with identical or different element configurations. Included among these examples was a design with 32 identical elements that achieved a 42% array-length reduction and a 16% element-size reduction, while providing a relative sidelobe level less than −10 dB and a VSWR less than 2∶1 for each element over the scan range of ±30° from broadside. [ABSTRACT FROM PUBLISHER]