Showing papers by "Per-Simon Kildal published in 1993"

Admittance of an isolated waveguide-fed slot radiating between baffles using a spectrum of two-dimensional solutions

Abstract: An efficient method of computing resonant length and admittance characteristics of an isolated broad-wall shunt slot radiating between baffles of finite height is presented. The outer three-dimensional (3D) field problem associated with this geometry is reduced to a two-dimensional (2D) one via a Fourier transformation with respect to the longitudinal z direction. For each value of the longitudinal wave number k/sub z/ an integral equation is solved for the E field in the mouth of the plates using the method of moments. This procedure is repeated for several discrete values of k/sub z/, to obtain a spectrum of 2D solutions which are then inverse-transformed to construct the 3D solution in the spatial domain for the exterior baffle region and the half space. The slot aperture field is determined by the conventional moment method solution to the integral equation that enforces the continuity of the H field across the slot. Scattering properties of the slot are then deduced. Numerical results for the resonant length and resonant conductance are presented. Computer results are found to be in good agreement with experimentally measured data. >

Artificially soft and hard surfaces in electromagnetics and their application to antenna design

Abstract: This paper give an introduction to the concept of artificially soft and hard surfaces in electromagnetics. The soft and hard surfaces are defined from the boundary conditions of the E-field by an analogy with soft and hard surfaces in acoustics. The electromagnetic soft and hard surfaces have polarisation-independent boundary conditions (at the centre frequency), in contrast to a metallic conductor that has different boundary conditions for the tangential and normal components of the E-field. This makes the soft and hard surfaces desirable in many practical antennas, in particular when dual or circular polarisation is required. The soft and hard surfaces are realised by providing a metal conductor by an anisotropic surface impedance. This can be obtained by providing it with corrugations, or with a strip-loaded dielectric layer. The most known application of the soft surface is in hybrid-mode horns, more commonly known as corrugated horns. The corrugated "soft" surface is also often called "chokes" and used to reduce coupling and sidelobes in particular directions (e.g. choke-horn). The hard surface has only been known a few years. Two of the most important applications of the hard surface are described in the present paper. The first is to design hard horns which have very high aperture efficiency for application in cluster feeds and arrays. The second is to reduce scattering from masts or struts that block the aperture or radiation fleld of an antenna. The paper also describes how known calculation methods now are extended to analyse these types of loaded surfaces.

An efficient rectangular hat feed for linear polarization and low sidelobes

Abstract: A cheap alternative to the swan-neck feed, which can obtain low sidelobes even without an absorbing cylinder is presented. This feed is called the rectangular hat feed. The ideas of soft and hard surfaces have been used to optimize the performance of this linearly polarized feed. It can give low sidelobes and has broader bandwidth than the circular hat feed. >

Admittance of a longitudinal slot in a finite ground plane

Abstract: The admittance and resonant length of an isolated longitudinal waveguide slot radiating in a finite ground plane are calculated. The problem is solved by applying a spectrum of two-dimensional solutions, referred to as the S2DS method. The reflection coefficient of a single slot in a WR-187 terminated waveguide was measured as a function of slot length and slot offset at 4.8 GHz. This makes it possible to determine the resonant length and resonant conductance for the slot. The resonant length is predicted within 0.5%. >