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

An iterative solution method (POHM iterative) has been developed which is suitable for modelling small, intricate antennas that are mounted on comparatively large bodies. The method provides radiation pattern, impedance, gain and RCS information. A computer program was developed to test the POHM iterative algorithm. Results shows good agreement with moment method calculations and experimental data.

Iterative improvement of physical optics hybrid method-POHM iterative

The pioneering work of Maxwell (1864), Hertz (1888), Marconi (1895), Jansky (1948) and many other prominent researchers brought us the age of personal communications and sophisticated astronomical observations. The technological demands in fulfilling these dreams are vast and cover a multi-disciplinary usage of broad-based innovative engineering developments. Among the prominent technological challenges the applications of high performance antenna designs are one of the prime elements of the successful implementations of these systems. Reflector, lens and horn antennas are an integral part of both the satellite payload and a key component in the radio astronomy and remote sensing radar. This article looks at the historical events and then highlights several exciting developments by providing an overview of modern developments in the arenas of communications, remote sensing, radio astronomy, etc.

Reflectors, lenses and horns: past, present and future

For aperture type antennas in space applications, a thin radome in the mouth of the antenna is often employed. This radome is typically constructed of a layer of dielectric with a coating of paint on the exterior surface. Usually, the dielectric and paint can be made to be very thin as compared to the free space wavelength, and thus one anticipates that (for reasonably low loss material) the effect of the radome on the far-field is negligibly small. One must consider the antenna and radome interactions to properly account for the effects of the radome since the radome is typically in the near-field of the antenna. When the full interactions are taken into consideration, the loss can be considerably larger than the loss predicted by a simple plane wave transmission loss. For applications like scatterometer systems where the gain level in extended angular range is critical, or in systems for which the G/T level must be predicted accurately, the net radome loss can be significant. This radome loss is studied for a specific antenna geometry. It is shown that the loss in peak gain due to a radome is noticeably larger than that predicted by a plane wave analysis. >

Characterisation of the effects of thin radomes on antennas for space applications

Several emerging technologies such as next generation CubeSats and 5G mm Wave networks require antennas capable of providing high data rates while maintaining a small form factor. This paper describes a systematic approach for synthesizing high gain stepped reflector antennas with profile heights of the order of a wavelength, resulting in a very small form factor for mmWave bands. The reflector aperture is comprised of confocal parabolic sections which scatter in phase, resulting in a focused far field beam. Both symmetric and offset configurations are discussed. In particular, two distinct methods of synthesizing low profile offset reflectors are presented in this work, which makes it possible to meet application specific design constraints.

Novel Metal Only, Low Profile, High Gain Stepped Reflector Antennas for Future 5G mmWave and CubeSat Applications

http://ieeexplore.ieee.org/iel6/8258/25864/01149726.pdf

Yahya Rahmat-Samii

Papers

Iterative improvement of physical optics hybrid method-POHM iterative

Reflectors, lenses and horns: past, present and future

Characterisation of the effects of thin radomes on antennas for space applications

Novel Metal Only, Low Profile, High Gain Stepped Reflector Antennas for Future 5G mmWave and CubeSat Applications

Lens feed concepts for electronically steerable mobile satellite array antennas