Motivated by the critical challenges posed by modern wireless data trends and RFIC layouts, an aperiodic phased array topology that remains scalable to an arbitrary number of elements is proposed. Facilitated by an analytical surrogate directivity model of realistic embedded elements in an arbitrary planar array, such scalable aperiodic layouts are inversely designed for several element counts and representative cosine element patterns. It is seen that the proposed topology can operate over a wider bandwidth and field of view (FOV) than counterpart periodic arrays, yet with similar maximum gains across more than an octave of operation. Moreover, the use of the surrogate directivity model in the inverse design of these arrays bears out, for the first time, the importance of considering an array's embedded element pattern during the design process, not just after. It is shown that this process, which represents a significant break from the traditional optimization approaches, can yield array designs with superior performance.

The design space for electrical small antennas (ESAs) is being constantly innovated and transformed through the development of new technologies, materials, and design techniques. The thematic goal of these efforts is to balance the fundamental physical limitations imposed by the electrical miniaturization of the antenna with the application-driven need to enable broadband performance of the system. The fundamental challenges are well described by well-known limits linking the quality factor and bandwidth of the antenna (e.g., Chu's Limit) as well as the performance of any lumped, distributed, or hybrid circuit topology that may be deployed for small-signal impedance matching (e.g., Bode-Fano Limit). There are a wide range of pragmatic challenges that also exist that compound the complexity of this design space; this includes, but it not limited to, the losses and non-ideal behavior of commercial off-the-shelf components and materials and its interaction with a ground plane or the platform it is integrated onto. A recent concept using the Antenna-As-Package (AAP) has emerged in the mm-wave community to reconcile the dimensional similarities of active circuits (amplifiers, etc.) with the antennas, and it is examined here in the co-design of the ESA and a custom/co-located RFIC. This talk will include strategies explored to integrate time-varying impedance matching and large-signal matching into the ESA to maximize power radiated by the antenna when transmitting and maximize the SNR when receiving. Since typical antenna performance metrics (VSWR, etc.) becomes challenging to define in this configuration, the ESA's ability to transmit/receive phase-based digital communication schemes (N-QAM, OFDM, etc.) ais compared to an electrically large wideband antenna (horn, etc.). Simulated and measured results will be provided along with a discussion on the external limiting factors that also drive the performance of the system.

In this invited paper, the New Technology Directions Committee (NTDC) of the IEEE Antennas and Propagation Society (AP-S) presents new and emerging research directions to commemorate the 70th anniversary of the IEEE Transactions on Antennas and Propagation. The NTDC consists of three working groups (WGs); the members and collaborators of these groups provide their perspectives on topics related to WG themes in this article. WG-1 focuses on the advancement of materials and manufacturing processes for future antenna applications. WG-2 focuses on advances in communications, sensing, and imaging. WG-3 focuses on maximizing the societal impact of wireless connectivity. The discussion in this article ranges from additive manufacturing (AM) techniques and system integration to advanced communications and quantum-based sensing technologies. Numerous applications are explored and a perspective on the digital divide is offered.

In this paper, the design of an $8 \times 8$ Butler matrix, for fabrication with additive manufacturing, is presented. The use of additive manufacturing offers more design flexibility, with the opportunity to design parts in 3-dimensions. Individual component design (hybrid couplers, phase shifters, and crossovers) is presented along with simulated results. Additionally, the full Butler matrix design is presented along with simulated results.

In this paper, the effect of hardware errors is analyzed for phase-mode beamforming for uniform circular arrays. Distortion-mode errors due to array inter-element spacing is investigated along with hardware errors due to slight phase differences of an ideal and actual Butler matrix design. Phase-mode beamforming is carried out for using both ideal and real hardware implementations of the array and Butler matrix.

This work investigates and analyzes collaborative beamforming for a swarm-enabled distributed sensing project. It investigates the use of a three-dimensional, randomly populated, and uniformly-distributed array in three configurations: spherical, cylindrical, and cubical. These topologies uniquely act like a practical bound to contain the elements in swarm-type applications. In addition, these topologies provide mathematical simplicity toward understanding the fundamental research problem of both surface and underwater swarm-based UUV sensor networks, and their constraints to implementing a physical system in a volumetric setting. Therefore, statistical, ensemble, mean-valued average beampatterns scanned at the meridian elevation plane are analyzed in closed form using a large population of one million elements densely populated amongst geometrical bounds. This large density profile applies the law of large numbers in which numerical beampatterns converge to their expected (mean) patterns. Faithful agreement of the solution is shown to validate the distributed array pattern behavior. Finally, additional simulations are provided in this work using a cylindrical manifold that comprises ten, fifty, and one hundred isotropic radiators to determine the feasibility of a small element population.

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.

Flexible hybrid electronic (FHE) materials and devices exploit the interaction of mechanical and electromagnetic properties to operate in new form factors and loading environments, which are key for advancing wearable sensors, flexible antennas, and soft robotic skin technologies. Dielectric elastomer (DE) architectures offer a novel substrate material for this application space as they are a class of strain‐tolerant and programmable metamaterials that derive their mechanical and dielectric properties from their architecture. Due to their hyperelasticity, dielectric elastomers can leverage reversible finite deformation to physically reconfigure their internal architecture to repeatedly tune their material behavior. Here a combined computational and experimental study of two dielectric elastomer architectures, based on square and hexagonal unit cell periodicities are presented. A shift in effective permittivity is observed due to the relative increase in matrix volume and the rearrangement of the electric field distribution in the cells. Additive fabrication allows rapid unit cell geometry customization for tuning the electromechanical response of the architectures. Effective permittivity shifts Δ ε 2 > 0.7 under compressive strains of 35% are observed. The practical utility of this strain‐tunable permittivity is demonstrated in a microstrip patch antenna, which exhibits shifts in resonance frequency greater than 110 MHz when the dielectric elastomer substrate is compressed.

The design of an additively manufactured V‐band bandpass filter is proposed using spherical resonators with elliptical waveguides feeds. Compared with the traditional rectangular form, the curvilinear architecture seeks to mitigate corner radius effects in both the electromagnetic performance and additive manufacturing process. The filter and calibration components required for measurement are printed as single structures and then electroless silver plated using a closed‐loop bidirectional pump‐driven fluidic system. Simulated and measured results are provided.

Multi-material additive manufacturing enables transformative capabilities in customized, low-cost, and multi-functional electromagnetic devices. However, process-specific fabrication anomalies can result in non-intuitive effects on performance; we propose a framework for identifying defect mechanisms and their performance impact by mapping geometric variances to electromagnetic performance metrics. This method can accelerate additive fabrication feedback while avoiding the high computational cost of in-line electromagnetic simulation. We first used dimension reduction to explore the population of geometric manufacturing anomalies and electromagnetic performance. Convolutional neural networks are then trained to predict the electromagnetic performance of the printed geometries. In generating the networks, we explored two inputs: one image-derived geometric description and one using the same description with additional simulated electromagnetic information. Network latent space analysis shows the networks learned both geometric and electromagnetic values even without electromagnetic input. This result demonstrates it is possible to create accelerated additive feedback systems predicting electromagnetic performance without in-line simulation.

This work presents the design and fabrication of two multi-element structurally embedded vascular antennas (SEVAs). These are achieved through advances in additively manufactured sacrificial materials and demonstrate the ability to embed vascular microchannels in both planar and complex-curved epoxy-filled quartz fiber structural composite panels. Frequency-reconfigurable antennas are formed by these structures through the pressure-driven transport of liquid metal through the embedded microchannels. The planar multi-layer topology examines the ability to fabricate two co-located radiating structures separated by a single ply of quartz fabric within the composite layup. The multi-element linear array topology composed of microchannels embedded on to a single-layer are used to demonstrate the ability to conformally-integrate these channels into a complex curved surface that mimics an array of antennas on the leading edge of an Unmanned Aerial Vehicle (UAV). A parallel-strip antipodal dipole feed structure provides excitation and serves as the interface for fluid displacement within the microchannels to facilitate reconfiguration. The nominal design of the SEVAs achieve over a decade of frequency reconfiguration with respect to the fundamental dipole mode of the antenna. Experimental and predicted results demonstrate the operation for canonical states of the antennas. Additional results for the array topology demonstrate beam steering and contiguous operation of interconnected elements in the multi-element structure.

A system performance analysis for Direction of Arrival (DOA) estimation using UAV swarms in the presence of small sensor gain, phase, and position errors has been derived analytically. Its analysis accounts for pragmatic errors and uncertainties when the UAVs fly in practice. This includes the signal model with deterministic unknown location errors, which is extended to cases when the location error is stochastic. The Cramer-Rao Bound (CRB) is derived for the joint estimation of DOAs, accounting for variation in sensor gain, sensor phase, and sensor location errors for the swarm. This work examines the results from the first experimental campaign to study the behavior of these systems in a laboratory setting. Both numerical simulations and practical experiments have been obtained to verify the theoretical results. The focus of this manuscript is on the latter.

Recent studies demonstrate the benefit of integrating origami in many engineering applications, where computational methods facilitate the origami design process. An emerging concept utilizes origami design for physically and functionally flexible electromagnetic devices. However, coupled mechanical and electromagnetic design tools are needed to systematically navigate the complex spaces of fold topology and electromagnetic performance. In this article, we introduce topology optimization formulations that find origami fold-driven frequency selective surface designs possessing electromagnetic filtering properties at target frequencies. These formulations utilize a nonlinear mechanics analysis to simulate an origami folding process. A geometric mapping relates mechanically-relevant origami substrate properties and electromagnetically-relevant conductive element properties. Both gradient-based and genetic algorithm methods are used to find optimal origami crease patterns and folded configurations by optimizing fold stiffness and force distributions over a prescribed potential fold line network. Using nonlinear manifold learning techniques, we demonstrate the isolated nature of optimal design candidates in the design space and the complex interplay of fold topology and fold path selection through initial perturbation from the flat state. Collectively, this study provides an initial framework to design novel EM origami structures and also provides important insights on the complex nature of the design space, which can be leveraged to refine future tool development.

The design of an additively manufactured circular waveguide 3-dB hybrid directional coupler is proposed and demonstrated. Asymmetric corner radius perturbations at the in-plane orthogonal junction of the four waveguides along with curvilinear inductive posts designed to interact with the TE 11 mode of the circular waveguide are used to facilitate directivity and isolation. Capacitive waveguide perturbations at each of the four ports provide impedance matching. The proposed design is engineered to operate within V-band from 57 to 64 GHz and provide both 10-dB isolation and return loss and a 90° phase difference between the direct and coupled ports. A commercially available stereolithography (SLA) printer is used to fabricate the hybrid coupler as well as the rectangular-to-circular tapered mode transducers and the thru, reflect, line (TRL) calibration components required for experiments. The printed couplers are metallized using an electroless silver plating process by a closed-loop bidirectional multiport pump-driven fluidic system. Results from the experiment and the simulation are provided.

This work examines the characteristic modes and measurement of various circularly distributed array topologies in which element radiators are used independently to deliver both sum and difference beams under lossy conditions. An associated moment generating function is derived, such that analytical patterns use even-odd symmetries for sum difference beam behavior. This approach generalizes the Fourier probabilistic methods by using the Laplace transform to analyze statistical averages catering to the degenerating effects of pattern behavior that is influenced by the environment.

This work discusses the design of a microstrip patch antenna and its use as an orientation-agnostic radiator in an origami-inspired folding antenna array. The antenna is based on a perturbed circular patch design that is impedance matched to reside in a radial feed network for a 2 × 2 array. This 2 × 2 array can be switched to provide sum and difference pattern behaviour. Both the feed network and the ground plane are modified to enable folding of the structure according to the Miura-ori pattern. The performance of a circularly polarised array is evaluated for a comprehensive range of fold angles to evaluate the impact of physical reconfiguration. Results for a simulated and fabricated circularly polarised array are provided for a 3 GHz design.

In this work, a novel technique using closed-form expressions is rigorously surveyed to collaboratively nullsteer uniformly distributed, planar ring, and volumetric shell distributions. To assess the radiation behavior of these geometries circular tapers is of interest for their attractiveness in derivation, design, application, and mathematical simplicity. A rigorous mathematical derivation is used for the generation of closed-form expressions of the mean-valued radiation characteristics. The numerical simulations are performed using both ANSYS HFSS and MATLAB using a finite-element distribution. To validate the analytical models, we include the measured results of a uniformly distributed ring array topology, constrained to a set of 18 elements and a uniformly distributed shell array topology constrained to 16 elements. The results of all methods are compared to demonstrate exceptional agreement in the recommended theoretical analysis. This process follows differently from traditional phased array nulling methods, which apply the unique amplitude tapers along individual phased array elements. Unlike typical adaptive beamforming algorithms, this process does not require the estimation of second-order statistical metrics and avoids expansions of large polynomial equations. It uses shared aperture characteristics in order to generate null beams simultaneously. This can also be extended to widen null widths from the compounding of these shared aperture distributions, which is shown in simulation.

This paper presents the design, fabrication, and characterization of a self-foldable Active Origami Reflector Antenna (AORA) of parabolic form. Self-folding of the AORA is enabled by smooth uncreased folds composed of shape memory polymer (SMP) composites. Design methods for origami with smooth folds are applied to determine the shape and fold pattern of a planar sheet that can be folded to reach the parabolic antenna shape. A proof-of-concept prototype of the AORA is fabricated and self-folding of the AORA driven by thermal actuation of the SMP composite folds is demonstrated. The far-field electromagnetic (EM) characteristics of the AORA prototype are investigated through numerical simulations and experimental measurements in an anechoic chamber. A design-of-experiment study is conducted to investigate the effects of the antenna shape parameters on its EM characteristics such as far-field antenna gain and beamwidth, and to compare the performance of the AORA to that of equivalent smooth and faceted parabolic reflectors. Applications of the AORA include high-gain directional radio telescopes and satellite telecommunication.

A polarization reconfigurable microstrip patch antenna is achieved using eutectic gallium indium (EGaIn) confined in microfluidic channels. The antenna topology is derived from an orthogonal overlay of two linearly polarized narrow-width microstrip patch antennas. The resulting structure isolated each patch around a common feed structure that has a microfluidic network embedded into a superstrate. Reconfiguration occurs by the reversible filling and extraction of the liquid metal through the back plane of the antenna into microchannels that provide interconnections to the feed point. The microchannels are fabricated using 3D printing of a sacrificial ink in a thermally stable structural low-loss epoxy.

This paper reports on the direction-of-arrival (DOA) estimation using micro-UAV swarm-based (MUSB) arrays in the presence of location errors. The MUSB array is a virtually three-dimensional (3-D) random time-varying array reconstructed from swarming UAVs (unmanned aerial vehicle). In practice, the sensor position errors cannot be omitted and will impact the DOA estimation performance. The goal of this work is to evaluate the impact of the position errors in the proposed MUSB array and study the convergence under low snapshot conditions using the iterative Multiple Signal Classification (iterative- MUSIC) algorithm. Measurements on a thirty location test platform are provided to benchmark the performance with expectations.