There has of late been a great amount of interest by the antenna design community in the synthesis of optimal phased arrays. It is no wonder, given the increased prevalence of applications such as electronically steered radar, terrestrial multiuser communications (e.g., 5G mobile communications), and space-based shaped beam antennas, among many others. A key figure of merit in the design of a phased array is the directivity pattern, meaning both the peak achievable directivity ( D-0 ) of the array as well as the peak sidelobe level (PSLL) below the main beam. Especially in the case of large element-count aperiodic arrays, these values are quite difficult to accurately determine without first performing computationally intensive numerical integrations of unpredictable radiation patterns. The literature offers several solutions to determine directivity using analytical (i.e., closed form or exact) array factor (AF) methods, but these leave much to be desired in terms of true generality. In this work, we present a new fully generalized analytical directivity solution that may be applied to planar arrays of totally arbitrary topology. The proposed element model is shown to apply to a variety of practical antennas, in addition to enabling rapid array synthesis. Moreover, the solution is shown to be in excellent agreement with prior solutions when considered as special cases (SCs).

AbstractA lens consisting of an anisotropic near‐zero index metamaterial (NZIM) is introduced for improving the far‐field performance of active electronically scanned arrays (AESA). Several simulation studies demonstrate how the NZIM lens (metalens) can be functionalized to transform the embedded element pattern of an array from a typical cosinusoidal shape to a flat‐topped pattern, dramatically reducing the gain at wider angles. This corresponds to reductions in scan loss and suppression of grating lobes in the desired field of view (FOV), especially for arrays with large element spacing (i.e., sparse or thinned arrays). The metalens concept is demonstrated through several simulation studies illustrating the beam shaping capability of NZIM materials. A fabricated metalens demonstrates full suppression of grating lobes and minimal scan loss with a ±10° FOV, which is ideally suited for limited FOV applications such as geosynchronous satellite communications.

The operation and application of high-power microwave devices is limited by system cost and dielectric breakdown events. Reflectarrays, though, provide a promising lower-cost alternative to phased array solutions, while maintaining a low profile, reduced complexity, and lower weight requirements when steering compared with large reflector antennas so long as their resonant field enhancement is suppressed. However, reflectarrays are limited by their spatial feeding arrangement where the amplitude distribution can only be controlled by the feed choice and position. In this work, we briefly introduce that an additively manufactured gradient index (GRIN) lens can be optimized to engineer the near field reflectarray illumination from a conventional horn antenna to increase the power handling capacity of the array. In particular, the lens is shown to reduce the peak field strength by 17% across the aperture and correspondingly increases the aperture efficiency of the system from 70% to 75.9%, improving the effective radiated power by nearly 50%.

A universal mathematical model for the radiation pattern of an antenna has recently been introduced which promises to enable rapid and versatile array synthesis. Here, that model is utilized in a case study to illustrate the dramatic reduction in time-to-synthesis for a series of aperiodic linear arrays to meet a desired peak relative sidelobe level. The results indicate high computational efficiency compared to traditional numerical directivity methods.

Phased array technology has of late enjoyed a dramatic increase in utility in such varied applications as millimeter-wave communications and reconfigurable intelligent surfaces [1]. The increased use of this important enabling technology warrants strong design capabilities, to include rapid and accurate modeling of expected array behavior. To that end, we present in this report a new element pattern model which faithfully reproduces practical real-world, arbitrary array elements. Also, spherical integration of the proposed model results in a completely analytical solution, allowing for greatly reduced computational complexity in the optimization of arbitrary array topologies.

Metasurfaces have been used to greatly enhance the performance capabilities of well-known antennas. One example of this improvement in performance is the Advanced Short Backfire Antenna (A-SBFA), in which the metallic inner rim-wall of a short-backfire antenna is lined with an anisotropic impedance metasurface. A hexagonal A-SBFA has been shown to produce greater than 90% aperture efficiency at both the GPS L1 (1.575 GHz) and L2 (1.227 GHz) bands [1], while circular A-SBFAs are capable of greater than 100% dual-band aperture efficiency at a range of aperture sizes [2]. The A-SBFA technology is therefore an excellent candidate for service as an array element on next-generation Medium Earth Orbit (MEO) GPS satellite buses. In this report, we outline the development path that led to the current A-SBFA technology. We further describe studies which should be conducted to bring the A-SBFA to a higher level of technology readiness as a phased array element.

The feed for reflectarrays and transmitarrays is crucial for determining the overall antenna aperture efficiency, gain, and power handling. In the past, several methods, such as altering the horn shape to achieve higher modes, have been employed to modify the feed radiation pattern to improve these key parameters. However, another approach is to use gradient index (GRIN) lenses, which offer unprecedented control over the radiation pattern and can be used to shrink the overall antenna. In this paper, we demonstrate highly effective approaches for optimizing GRIN lenses to achieve different design objectives including high gain radiation with a compact feed as well as improved aperture efficiency and power handling. Additive manufacturing is employed to fabricate the lenses, and measured results agree well with simulations.

Reflectarray antenna (RA) systems are being increasingly used in many applications due to the advantages of their simple design and spatial feeding along with their capabilities for beam shaping and beam forming. However, like all aperture antennas, RAs are limited in the maximum gain they can achieve and power handling they can attain as a result of the feed illumination. By augmenting an RA horn feed with a GRadient INdex (GRIN) lens it is shown that it is possible to better distribute the feed's incident illumination across the surface while still maintaining the gain of the nominal system. Specifically, this work demonstrates that a GRIN lens designed for an offset fed RA at S Band operation can reduce the peak field strength by 17.6 % and correspondingly improve the power handling capability by 47% relative to the nominal, no-lens system.

The millimeter wave (mmWave) spectrum promises improved communications, but comes with the challenge of developing steerable, highly directive antennas which are operable over wide bandwidths. For mmWave systems, engineers often employ RF integrated circuit (RFIC) technologies for which scalable architectures are highly desirable. Periodic arrays, easily scaled to large apertures, are nevertheless hindered by grating lobes and inter-element coupling, which necessarily limit the operating bandwidth. Therefore, we present in this work a new aperiodic array topology which is supported by an underlying periodic feeding layer. Antenna element aperiodicity renders grating lobes virtually non-existent at wide steering angles, while feed point periodicity maintains RFIC scalability. Furthermore, this new topology is shown to be rapidly optimized with modern algorithms and verified by analytical formulations.

In this article, we demonstrate that a circular advanced short backfire antenna (A-SBFA) can be optimized for high single- or dual-band aperture efficiency over a range of different aperture sizes. Optimization methods developed previously to utilize anisotropic, dispersive metasurfaces on the cavity walls of the hexagonal A-SBFA are modified and applied to achieve 100% aperture efficiency at two frequency bands for circular aperture diameters spanning a remarkably large range from $1.0\lambda _{0}$ up to $2.13\lambda _{0}$ . Furthermore, a single-frequency optimization was able to achieve a design with 100% aperture efficiency for an A-SBFA with a diameter of $2.6\lambda _{0}$ , the highest known achievable efficiency for an antenna of its aperture size, and overall height. Finally, simulations revealed the first compact hard horn or open-ended waveguide design with close to 100% aperture efficiency below $1.6\lambda _{0}$ .

First introduced decades ago, the Short-Backfire Antenna (SBFA) has proven to be a well-defined, reliable, and rugged radiator often selected for use in harsh environments requiring gain greater than 15 dBi. In this report, we present the optimization of a circular Advanced Short Backfire Antenna (A-SBF A) which has been designed for dual-band operation with remarkably high aperture efficiency over a range of different aperture sizes. In contrast to the hard-EM SBFA, anisotropic, dispersive metasurfaces line the cavity walls of the circular A-SBF A and prove integral to achieving 100 % aperture efficiency at the two frequency bands for diameters spanning a range from $\boldsymbol{1.0\lambda_{0}}$ up to $\boldsymbol{2.13\lambda_{0}}$ . We present an inverse-design methodology used to optimize such high-performing A-SBFA antennas, and the pursuant results. In addition, we draw a comparison between the circular A-SBFA and traditional high-efficiency short horn antennas, which is illustrative of the great impact of the circular A-SBFA.

This work presents a new analytical (i.e., closed-form) solution to the directivity of a planar array with arbitrary topology. The derived method also makes use of a novel element pattern model which can take into account radial asymmetries in both θ and ϕ: a generic pattern suitable for a wide range of applications. The analytical method is validated by numerical integration using Simpson's 1/3 rd method. The analytical method enables fast topology optimization of phased array designs by avoiding time-consuming numerical integration.

A novel curvature-based shaped reflector antenna design technique using the covariance matrix adaptation evolution strategy (CMA-ES) algorithm is presented. An approach based on optimizing the profile of a curve representing a rotationally symmetric reflector is proposed. In this method, the reflector shape is optimized with few design variables and an ideal design is found within a very small number of iterations. The validity of this method is verified by an application example and its advantages are compared with a reflector surface represented using the modified Jacobi polynomials.

Metamaterial reflectarray antennas are attractive options for reducing system SWaP (size, weight, and power) compared to conventional reflector antennas. However, it has been a long-held belief that metamaterials are unsuitable for high-power microwave applications due to their strong field enhancement behaviors. Here we demonstrate that, fortunately, this challenge can be overcome by judiciously combining state-of-the-art optimization with intelligent material selection and metamaterial geometry.

A slotted waveguide antenna array (SWAA) has been optimized for high power microwave (HPM) applications in the L-band. Through the use of global optimization, the dimensions of the feed layer and radiating slots were fine-tuned to minimize S 11 and electric field enhancement, while maintaining high directivity. The radiating slots are encapsulated in dielectric, minimizing the electric field magnitude in air, while allowing the SWAA to be pressurized to further improve power handling capability.