Michael W. Nurnberger

Slot spiral antenna

When compared to printed cavity-backed spirals, slot spiral antennas offer the possibility of designs that are conformal and very thin. We discuss the physical characteristics of a cavity-backed slot spiral, as well as the associated infinite balun and termination designs. Simulations of the proposed cavity-backed spiral are presented and used to optimize the antennas various parameters. Comparisons of measurements and calculations are also given, to validate the gain and axial-ratio computations. Several options for miniaturizing this design, using capacitive and inductive loadings, are also presented.

A new planar feed for slot spiral antennas

A new planar, wideband feed for a slot spiral antenna is presented and tested at VHF frequencies. Radiation pattern measurements are presented to demonstrate the performance and usefulness of this feed. In contrast to most traditional printed spiral antenna designs, the one presented here incorporates a completely planar balun and feed, making it more attractive for conformal applications.

A hybridization of finite-element and high-frequency methods for pattern prediction for antennas on aircraft structures

This paper considers the hybridization of the finite-element and high-frequency methods for predicting the radiation pattern of printed antennas mounted on aircraft platforms. The finite-element method is used to model the cavity-backed antennas, whereas the interactions between the radiators and the substructures are treated via a high-frequency technique, such as the GTD, PO/PTD, or SBR. We present comparisons between measurements and calculations, along with a qualitative description of the finite-element and high-frequency codes employed.

A planar slot spiral for multi-function communications apertures

A slot spiral antenna and its associated feed are presented for conformal mounting on a variety of land, air, and sea vehicles. By exploiting the inherent broadband behavior, good pattern coverage and polarization generality of the spiral antenna, a conformal antenna which may be concurrently used for cellular, digital personal communications (PCS), global positioning (GPS), and intelligent vehicle highway systems (IVHS), as well as wireless LAN networks, has been developed. A key requirement for achieving such broadband behavior (800-3000 MHz) is the availability of a frequency-independent planar feed and balun. Additionally, high quality, very broadband spiral arm terminations and cavity and waveguide mode suppression are also very important. After a general description of the slot spiral antenna and the above advances, pattern and gain data are presented across the entire frequency range of operation.

Analysis of the log-periodic folded slot array

In recent years then has been significant interest in conformal, low-profile, very wideband antennas. To this end various configurations of log-periodic antenna structures have been developed, mostly consisting of planar logarithmic spirals, toothed planar and wire structures, and the ubiquitous dipole array. Unfortunately, none of these designs easily lend themselves to low-profile, conformal mounting. A log-periodic antenna structure more suited to this type of mounting has been developed by Greiser and is called the log-periodic folded slot array (LPFSA). Accurate knowledge of the radiation patterns and impedance characteristics would facilitate the development and optimization of a design procedure for the LPFSA. The purpose of this investigation is to gain a more complete understanding of the LPFSA, with the goal of developing an optimized design procedure.<<ETX>>

Ultra wideband slot spiral with dielectric loading: measurements and simulations

The performance of a very thin conformal cavity backed slot spiral antenna for various dielectric loadings inside and outside the cavity is considered. An improved FE-BI code is used to numerically predict and estimate the antenna performance for various antenna parameters. Near-field data are used to estimate the miniaturization effects for various dielectric loadings. These data are correlated to the miniaturization effects extracted from the antenna gain. An archimedean slot spiral antenna 15.2 cm in diameter and 1.2 cm thin is designed, built and measured and results are compared to the simulation.

A thin cavity-backed Archimedean slot spiral for 800-3000 MHz band coverage

We show that cavity-backed slot spirals (rather than printed) are particularly attractive for conformal applications. Since slot radiation is enhanced by the presence of a shallow metal backed cavity, very thin (less than a 1/4 inch thick) antennas can be considered without compromising the spirals broadband performance. A specific design proposed by Nurnberger and Volakis (see 19th. Meeting and Symposium of Antenna measurement Techniques Association, Boston, Massachusetts, 1997) is considered for analysis and improvement.

FEMATS: a general-purpose scattering code using the finite element method

The focus of the article is the code FEMATS, developed at the Radiation Laboratory of the University of Michigan. FEMATS is a general-purpose code for computing the radar cross-section (RCS) of arbitrary three dimensional targets with material inhomogeneities. It employs state-of-the-art techniques in finite element modeling of open structures, the latest sparse matrix solutions and graphical user interface for pre- and post-processing of the geometry and data files. Although the code has been primarily used for finding the echo-area of targets, FEMATS can be easily extended to solve open domain problems related to antennas, microwave circuits and cellular phones. The power of FEMATS comes from two features inherent in the technique: (i) the ability to model complicated geometries in three dimensions having arbitrary material fillings without code modification; (ii) the O(N) memory requirement of the method due to the employed local mesh termination techniques conformal to the target. This feature essentially implies that the technique scales favorably with problem size and thus very large problems can be tackled with minimal usage of computer memory and time.