The electric field integral equation (EFIE) is used with the moment method to develop a simple and efficient numerical procedure for treating problems of scattering by arbitrarily shaped objects. For numerical purposes, the objects are modeled using planar triangular surfaces patches. Because the EFIE formulation is used, the procedure is applicable to both open and closed surfaces. Crucial to the numerical formulation is the development of a set of special subdomain-type basis functions which are defined on pairs of adjacent triangular patches and yield a current representation free of line or point charges at subdomain boundaries. The method is applied to the scattering problems of a plane wave illuminated flat square plate, bent square plate, circular disk, and sphere. Excellent correspondence between the surface current computed via the present method and that obtained via earlier approaches or exact formulations is demonstrated in each case.

Electromagnetic scattering by surfaces of arbitrary shape

A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. Although it is made of continuous metal, and conducts dc currents, it does not conduct ac currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves, and its image currents are not phase reversed. The geometry is analogous to a corrugated metal surface in which the corrugations have been folded up into lumped-circuit elements, and distributed in a two-dimensional lattice. The surface can be described using solid-state band theory concepts, even though the periodicity is much less than the free-space wavelength. This unique material is applicable to a variety of electromagnetic problems, including new kinds of low-profile antennas.

/pdf/high-impedance-electromagnetic-surfaces-with-a-forbidden-3vtu72a5an.pdf

High-impedance electromagnetic surfaces with a forbidden frequency band

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

The particle swarm optimization (PSO), new to the electromagnetics community, is a robust stochastic evolutionary computation technique based on the movement and intelligence of swarms. This paper introduces a conceptual overview and detailed explanation of the PSO algorithm, as well as how it can be used for electromagnetic optimizations. This paper also presents several results illustrating the swarm behavior in a PSO algorithm developed by the authors at UCLA specifically for engineering optimizations (UCLA-PSO). Also discussed is recent progress in the development of the PSO and the special considerations needed for engineering implementation including suggestions for the selection of parameter values. Additionally, a study of boundary conditions is presented indicating the invisible wall technique outperforms absorbing and reflecting wall techniques. These concepts are then integrated into a representative example of optimization of a profiled corrugated horn antenna.

Particle swarm optimization in electromagnetics

A reflectarray utilizes key features of reflector antennas and phased array antennas by allowing a feed to illuminate its planar main reflector's array elements to produce a collimating beam. Consequently, this mechanism eliminates the feed-network as required in phased-array antennas. Maximizing the reflectarray antenna gain requires a phase correcting mechanism to be applied to its individual array elements. Phase correction can be achieved in a number of ways by maintaining phase uniformity across the reflectarray surface. Independent of the type of phase compensation scheme, in this study, we attempt to extend analytical techniques in reflector analysis to reflectarray antennas by introducing a number of approaches to estimate the reflectarray antenna performances.

http://ieeexplore.ieee.org/iel5/8636/27413/01219847.pdf

Characterizing reflectarray antennas radiation performance

An electrically large antenna system is vulnerable to the interference with other communication links. An accurate and fast prediction of antenna coupling can reduce an adverse effect of the interference in preliminary stage of antenna system design. In this paper, the integral form of coupling formula is employed in examining the mutual coupling between two antennas placed in the near-field and far-field region. It demonstrates the feasibility of applying the coupling program to diverse cases of mutual coupling.

Calculation of Mutual Coupling between Two Antennas of Diverse Displacements and Polarizations

The vision of Internet of Things (IoT) has evolved the needs of providing seamless connectivity between devices across the globe. A potential solution to this requirement is to launch a CubeSat constellation that can provide broadband Internet access to rural and undeveloped areas (Internet of Space (IoS)). This has escalated the need for low-cost, low-profile antennas with wide angle beam steering capabilities. In this work, we elaborate on the design of a broadband, circularly polarized reflectarray capable of dynamic beam steering in the frequency range of 17.8-20.2 GHz. The reflectarray unit cell consists of a set of four copies of rotated Archimedean spiral arms, and the desired phase shift is obtained by suitably switching between these arms through PIN diodes. Representative prototypes have been fabricated and measured, and beam scans up to 60° have been achieved.

Beam Steerable Reflectarray Enabling CubeSat Internet of Space: Conceptualization and Design (Invited Paper)

With the advent of small-scale satellite technologies, there has been significant interest in developing deployable antennas for CubeSat and SmallSat projects. This paper introduces a novel concept of deployable lenses based on impedance matching gradient index (GRIN) metamaterials. The three-dimensional lens antenna consists of multi-layer microstrip square-ring units of variable sizes distributed on planar substrates to satisfy the required refractive index distribution. The attractiveness of this new lens is its high performance and low-profile. Developing lenses within this paradigm opens the door for many new applications which require compact and high-gain antennas.

A Novel Deployable Compact Lens Antenna Based on Gradient-Index Metamaterials

This paper investigates elliptic-card antennas in terms of feeding techniques and feasibility of miniaturization of these antennas. Starting from an available design, the structure antenna is modified and the feeding mechanism is designed. The performance of the antennas is then simulated in terms of VSWR and far-field patterns and the results are verified by measurements. In the next step, it is shown that the length of the antenna can be miniaturized by a factor of 4. The miniaturized antenna is built and measured to verify the simulation results. In the course of this study, the structures of antennas are simulated using HFSS software and the results are verified by measurements. The results represented in this study propose the miniaturized elliptic-card antenna as an efficient and ultra wideband (3.1 to 10.6 GHz) antenna which can be considered as an attractive candidate for portable ultra wideband communication devices

Yahya Rahmat-Samii

Papers

Characterizing reflectarray antennas radiation performance

Calculation of Mutual Coupling between Two Antennas of Diverse Displacements and Polarizations

Beam Steerable Reflectarray Enabling CubeSat Internet of Space: Conceptualization and Design (Invited Paper)

A Novel Deployable Compact Lens Antenna Based on Gradient-Index Metamaterials

Elliptic-Card UWB (3-11 GHz) Antennas for Wireless Communications: Miniaturization, Simulation and Measurement