We experimentally demonstrate a frequency-diverse, computational imaging system at W-band frequencies utilizing an array of cavity-fed metasurface antennas. Each metasurface antenna consists of a cavity milled from aluminum stock, with an upper plate patterned with a set of radiating slots. As a function of frequency, the metasurface cavities produce a set of spatially diverse radiation patterns that probe the reflectivity distribution of a scene. The antennas are designed to maximize the measurement diversity and hence imaging capacity of the system. The number and distribution of the radiating slots is optimized by balancing the cavity quality factor (Q) and Fourier space coverage. In the experimental realizations, the radiation patterns from each cavity-fed metasurface antenna is first measured using near-field scanning techniques, propagated over the imaging domain, and then stored for use in the image reconstruction step. Comprehensive alignment procedure is implemented to align the measured radiation patterns with regard to the physical position of the cavities. Using a modeling platform, we find excellent agreement between the simulation and experiment, indicating the validity of the calibration and alignment procedures. The scaling of the cavity-fed metasurface antenna represents a key step in the development of alternative high-frequency apertures for imaging and beam-forming applications.

We demonstrate a low-profile holographic imaging system at millimeter wavelengths based on an aperture composed of frequency-diverse metasurfaces. Utilizing measurements of spatially-diverse field patterns, diffraction-limited images of human-sized subjects are reconstructed. The system is driven by a single microwave source swept over a band of frequencies (17.5–26.5 GHz) and switched between a collection of transmit and receive metasurface panels. High fidelity image reconstruction requires a precise model for each field pattern generated by the aperture, as well as the manner in which the field scatters from objects in the scene. This constraint makes scaling of computational imaging systems inherently challenging for electrically large, coherent apertures. To meet the demanding requirements, we introduce computational methods and calibration approaches that enable rapid and accurate imaging performance.

We present a novel method of rapid prototyping waveguide and antenna using plating on plastic technique. The part is created by high-precision three-dimensional printing and plated with copper using both electroless plating and electroplating. The performance is comparable to industry-made waveguides and antennas, but the time and cost for creating these parts are largely reduced.

We design and numerically analyze a coherent computational imaging system that utilizes a sparse detector array of planar, frequency-diverse, metasurface antennas designed to operate over the W-band frequency range (75-110 GHz). Each of the metasurface antennas consists of a parallel plate waveguide, into which a center coaxial feed is inserted into the lower plate, launching a cylindrical guided wave. A dense array of metamaterial resonators patterned into the upper plate couples energy from the waveguide to free space radiative modes. The resonance frequency of each element, determined by its specific geometry, can be positioned anywhere within the W-band. The geometry of each element is chosen to produce a resonance frequency selected randomly from the W-band. Since a random subset of elements is resonant at any given frequency, the metasurface antenna forms a sequence of spatially diverse radiation patterns as a function of the excitation frequency. We analyze the metasurface aperture as an imaging system, optimizing key parameters relevant to image quality and resolution, including: aperture size; density and quality factor of the metamaterial resonators; number of detectors and their spatial distribution; bandwidth; and the number of frequency samples. A point-spread function analysis is used to compare the metasurface imager with traditional synthetic aperture radar. The singular value spectrum corresponding to the system transfer function and the mean-square-error associated with reconstructed images are both metrics used to characterize the system performance.

We present an analysis of a slotted waveguide antenna (SWA) whose directivity has been enhanced by using metamaterial parasitic elements. We apply an adapted form of the discrete dipole approximation (DDA) as a modeling tool and verify the accuracy and versatility of this method for different configurations, including matched and shorted SWAs, and with and without parasitic elements. The results presented in this letter demonstrate the capabilities of the DDA for the fast and accurate simulation of aperture antennas composed of small radiators, and its further application for the design of complex metamaterial structures.

In this article we introduce a new type of frequency diverse antenna based on a leaky waveguide. We have shown with simulated experiment that the antenna can achieve 2cm spatial resolution at K-band frequencies

The focus of this manuscript is an analysis of various design aspects of composite right-left handed transmission lines (TLs) with emphasis on practical implementation to periodic structures. Existing used design procedures consider the influence of a period to guided wavelength ratio, coupling of parasitic fields, or fabrication inaccuracies to a limited degree. These factors become especially important for composite right/left handed (CRLH) TLs design increasing the frequency of operation. The result of this work is a detailed analysis of finite periodic transmission lines design with regard on the factors mentioned. The optimal value of the period to guided wavelength ratio was found to be 0.1-0.25 for the best trade-off between easy balancing of the unit cell and maintaining the applicability of the Bloch analysis.

Bloch analysis in conjunction with a full-wave simulation is used in order to design a composite right/left-handed (CRLH) transmission line (TL). We analyze the parasitic components introduced by loading elements and inter-cell coupling, and present details to the compensation required in order to maintain the balanced state of the periodic TL. The method is shown to yield a useful tool for the design of CRLH periodic TLs up to millimeter-wave frequencies for structures with arbitrary metallization. The performance of the method is shown numerically at 26 and 77 GHz. Experimental verification is done at 26 GHz, comparing radiative properties, dispersion, and attenuation constant of a through-broadside scanning leaky-wave antenna.

This paper proposes a hybrid scanning antenna architecture for applications in mm-wave intelligent mobile sensing and communications. We experimentally demonstrate suitable W-band leaky-wave antenna prototypes in substrate integrated waveguide (SIW) technology. Three SIW antennas have been designed that within a 6.5 % fractional bandwidth provide beam scanning over three adjacent angular sectors. Prototypes have been fabricated and their performance has been experimentally evaluated. The measured radiation patterns have shown three frequency scanning beams covering angles from 11 to 56 degrees with beamwidth of 10 ± 3 degrees within the 88-94 GHz frequency range.

This paper discusses the prospects of millimeter-wave beam steering antennas, such as tuneable high-impedance surface, dielectric rod waveguide with an integrated phase shifter, tuneable leaky-wave antenna, active reflectarray, and shaped lens antenna with an integrated switched feed array. In these antennas the necessary phase change for antenna elements can be achieved using various electronically tuneable elements, but in our case MEMS are used. Some early results of our investigations are presented.

This paper describes the main results of the EU FP7 project TUMESA - MEMS tuneable metamaterials for smart wireless applications. In this project, we studied several reconfigurable antenna approaches that combine the new technology of MEMS with the new concept of artificial electromagnetic materials and surfaces (metamaterials and metasurfaces) for realisation of millimetre wave phase shifters and beam-steering devices. MEMS technology allows to miniaturise electronic components, reduce their cost in batch production, and effectively compete with semiconductor and ferroelectric based technologies in terms of losses at millimetre wavelengths. Novel tuneable materials and components proposed in this project perform as smart beam steering devices. Fabricated with MEMS technology in batch and on a single chip, proposed tuneable devices allow substituting of larger and more complex sub-system of, e. g., a radar sensor. This substitution provides a dramatic cost reduction on a system level.

Microelectromechanical (MEMS) technology is being used for many purposes in reconfigurable devices due to its advantages compared to other technologies, e.g., varactors. In this paper MEMS are suggested to be used for the development of leaky-wave antenna for 77 GHz. Antenna comprises a right left handed transmission line, where a microstrip is used as the right handed transmission line. The left handed loading comprises series reconfigurable MEMS capacitors and shunt narrow strip inductors. Analytical design, simulation and measurement of a planar leaky-wave antenna structure are carried out and compared.

The authors suggest and theoretically study an efficient leaky-wave antenna (LWA) with beam scanning governed by micro-electromechanical systems (MEMS) capacitors. The use of MEMS instead of varactors or magnetised ferrite substrate allows one to significantly decrease losses. The LWA is implemented as a periodically loaded transmission line (PLTL). In order to obtain maximal possible dispersion of a PLTL, resonant loads combining variable capacitors and stub strap inductors are applied. Analysis of dispersion properties and design of a unit cell of the PLTL are based on the analytical model with further numerical optimisation. Full-wave simulations are carried out for a realistic beam-scanning LWA, where the radiated beam can transit from forward to backward directions for a practical MEMS design.

This paper presents study of controllable leaky wave modes in various planar transmission lines operating at millimetre wavelengths. Leaky wave regime is achieved by exploitation of periodic inclusions. The main goal is to obtain the scanning of the radiation angle from forward to backward direction and rather broad range of scanning angles at a given operation frequency corresponding to the mm-wave range. For this purpose, we suggest to use MEMS capacitors combined with shunt strap inductors. This design solution allows one to significantly reduce the losses in the loaded line compared to known scanning leaky-wave antennas based on varactors, or on magnetized ferrites. The design of the unit cell is done using global optimization method, and the dispersion is investigated analytically. After that, full wave analysis is done using Ansoft HFSS v.11 environment. After the leaky wave regimes are verified, an example of a leaky-wave antenna is introduced in order to confirm possibility of beam scanning.

In this paper, design, analytical analysis and numerical analysis of beam-steering possibilities of the planar transmission line loaded with microelectromechanical systems (MEMS) capacitors and stub inductors is presented. First, the design and analysis of a single unit cell comprising antenna structure is carried out. By stacking certain number of these unit cells leaky-wave structure is obtained, which is then analyzed. As a result, effective beam-steering structure (controlled by MEMS capacitance variation) is obtained.

The paper is focused on numerical studies of electromagnetic properties of composite materials used for the construction of small airplanes. Discussions concentrate on the homogenization of composite layers with metal lattice and composite layers with metal lattice with a slot. The homogenization is aimed to reduce CPU-time demands of EMC computational models of electrically large airplanes. First, a methodology of creating a 3-dimensional numerical model of a composite material with metal lattice in CST Microwave Studio is proposed focusing on a sufficient accuracy of the model. Second, two different approaches to homogenizing the composite with metal lattice are discussed. The proposed approaches are evaluated and compared from the viewpoint of the efficiency, the accuracy, the convergence, and hardware requirements. The obtained field distribution is compared with the distribution computed for the original composite walls.