Stephen W. Schneider

Beam Steering of a Half-Width Microstrip Leaky-Wave Antenna Using Edge Loading

A technique is presented for steering the main beam of a half-width microstrip leaky-wave antenna (LWA) at fixed frequencies over the operational frequency range. By loading the free edge of the microstrip using lumped capacitors, the phase constant may be adjusted in a prescribed manner, and the beam pointed along a desired direction. The transverse resonance method is used to explore the range of capacitances needed to steer the beam through a nearly 90° range of angles for a typical antenna. Measurements of a prototype antenna are used to validate the technique.

Modeling conformal antennas on metallic prolate spheroid surfaces using a hybrid finite element method

In this paper, the hybrid finite element-boundary integral (FE-BI) method appropriate for modeling conformal antennas on doubly curved surfaces is developed. The FE-BI method is extended to model doubly curved, convex surfaces by means of a specially formulated asymptotic dyadic Greens function. The FE-BI method will then be used to examine the effect of curvature variation on the resonant input impedance of a cavity-backed, conformal slot antenna and a conformal patch antenna recessed in a perfectly conducting, electrically large prolate spheroid surface. The prolate spheroid shape provides a canonical representation of a doubly curved mounting surface. The numerical results for conformal slot and patch antennas on the prolate spheroid are compared as a function of curvature and orientation.

Radiation by a magneto-dielectric loaded patch antenna

Radiation by microstrip patch antennas have been studied for well over thirty years. Their popularity in array, especially for massive arrays, is due in no small part to their construction methods. They are, in the simplest configuration, a leaky capacitor consisting of a metallic patch sitting atop an electrically thin grounded dielectric slab. The antenna is fed in some manner and if designed well, will radiate over a rather narrow bandwidth of a couple percent. More capable microstrip patch antennas inevitably involve more complex construction and a fairly complex feed structure (since the most simple feed mechanism tends to limit the operational bandwidth). In this paper, a perturbation in the construction of the antenna is considered to provide another means to tune the behaviour of this ubiquitous radiator. This perturbation will involve the inclusion of loop inductors and a magneto-dielectric material.

Empirical analysis of the effects of parasitic elements on the half- width leaky wave antenna

Microstrip leaky wave antennas offer the potential for a low-profile, wide-bandwidth antenna element that can be arrayed if desired. An effort has commenced at the Air Force Research Laboratory (AFRL) to develop an array of these thin profile novel radiators in order to enhance efficiency and bandwidth. Understanding the effects of coupling and propagation effects of parasitic elements in an array environment is an essential stepping stone in this process.

Finite element-boundary integral simulation of a conformal microstrip leaky-wave antenna

Microstrip leaky-wave antennas offer an attractive wide bandwidth alternative to microstrip patch antennas with the caveat involving pattern control. Leaky-wave antennas, by their nature, will steer the main-lobe of the radiation pattern as the operating frequency is changed. Therefore, although the bandwidth of leaky-wave antennas is attractive, ensuring a fixed angle of radiation independent of the operating frequency, within the leaky-wave region of operation, is challenging.This is especially true for microstrip leaky-wave antennas that are conformally mounted on a curved surface, such as a circular cylinder. In this paper, a microstrip leaky-wave antenna is investigated and particular attention is paid to the radiation properties of the antenna. The antenna is simulated with a finite element-boundary integral formulation that makes use of a dyadic Greens function for an infinite, metallic, right circular cylinder.

Radiation and Scattering by Complex Conformal Antennas on a Circular Cylinder

A technique for characterizing and designing complex conformal antennas flush-mounted on a singly-curved surface is presented. This approach is based on the hybrid finite element–boundary integral (FE–BI) method. A related method was proposed in the past utilizing cylindrical-shell finite element and roof-top rectangular basis functions for the boundary integral. Although that method proved very powerful for analyzing cylindrical–rectangular patch arrays flush-mounted to a circular cylinder, the requirement for uniform meshing in the aperture ultimately limited its usefulness. In this present formulation, tetrahedral elements are used to expand the volumetric electric fields while similar basis functions are used for the boundary integral. The curvature of the aperture is explicitly included via the use of the circular cylinder dyadic Greens function. After presentation of the formulation and validation using several well-understood examples, an example is presented that illustrates the capabilities of this method for modeling complex conformal antennas heretofore not examined by rigorous methods due to inherent limitations of the various published methods.

Modeling conformal antennas on prolate spheroids using the finite element-boundary integral method

In this paper, the effects of curvature on the resonant input impedance and radiation pattern of a cavity-backed, rectangular, aperture antenna that is conformal to the surface of a perfectly conducting prolate spheroid are investigated. The radiation pattern and input impedance are calculated using a hybrid finite element-boundary integral approach. To gain further insight, the behavior of the resistive part of the resonant input impedance of the antenna is compared with that of the same type of antenna that is conformal to the surface of a perfectly conducting circular cylinder as the curvature is varied.

The design of wideband arrays of closely-spaced wire and slot elements

The quest for wide band operation of antenna arrays, for example reaching 10 to 1 or more, has led to the consideration of many different types of elements. Spirals and other wide band elements have been tried as one alternative, but this leads to large elements with wide interelement spacing that results in grating lobes at high frequencies. Munk [1, 2] has shown that simple dipoles and slots can be effectively used to achieve wide band widths without grating lobes by the effective use and control of element to element coupling and wide band matching techniques. This paper outlines the logic of this array design procedure. Many impedance calculations used in planar wideband array design are made using the Periodic Moment Method code [3]. The theory behind PMM is based on a plane wave expansion technique [4], and yields the analysis of infinite, periodic, and planar arrays of scattering elements (wires or slots). Semi-infinite calculations are made using a code referred to as SPLAT [5, 6].

Analysis of arrays of microstrip half-width leaky wave antennas

The research described in this paper continues that work by analyzing two four-element arrays of microstrip half-width leaky wave antennas of different element lengths. The experimental results are compared with calculations made using the commercial software CST Microwave Studio.

Simulation of Microstrip Leaky-Wave Antennas on Inhomogeneous Substrates Using Transverse Resonance and Finite Element Methods

Abstract Microstrip leaky-wave antennas offer the potential for wide-bandwidth, thin-profile apertures, albeit with the potential disadvantage of beam steering with respect to operating frequency. These antennas have been extensively studied in the past; however, previously published results have utilized homogeneous substrates. In this article, a substrate with transverse step inhomogeneous layers is investigated with two methods: the transverse resonance method (TRM) and the finite element-boundary integral (FE-BI) method. In this article, the former is generalized for N-layers and used to determine the leaky-wave mode propagating characteristics. Antennas designed using this approach are then simulated using the finite element method to determine the radiation pattern.