Showing papers by "Per-Simon Kildal published in 1988"
TL;DR: The widely used transversely corrugated surfaces and other alternative surfaces having the same anisotropic surface impedance deserve a common name as discussed by the authors, and it is proposed to call them soft surfaces by analogy with the soft surfaces in acoustics.
Abstract: The widely used transversely corrugated surfaces and other alternative surfaces having the same anisotropic surface impedance deserve a common name. Here it is proposed to call them soft surfaces by analogy with the soft surfaces in acoustics. In the same way artificially hard surfaces are defined. Cylindrical hard waveguides of any cross-sectional shape can support TEM waves.
349 citations
TL;DR: Horn antennas with soft and hard boundaries are analyzed and the dependency between the edge taper directivity, and sidelobes is calculated based on the solution to the spherical hybrid modes in a conical horn with arbitrary wall impedances.
Abstract: Horn antennas with soft and hard boundaries are analyzed. A soft boundary which exists in classical hybrid-mode horns gives zero field intensity at the wall. A hard boundary corresponds to a uniform field distribution over the horn aperture. Soft and hard horn antennas are compared with respect to directivity, sidelobes, and beamwidth. The dependency between the edge taper directivity, and sidelobes is also calculated based on the solution to the spherical hybrid modes in a conical horn with arbitrary wall impedances. This makes it possible to study how to compromise between directivity and sidelobes. Also discussed is how the different wall impedances may be realized, and some preliminary experimental work on hard horns is presented. >
102 citations
06 Jun 1988
TL;DR: In this article, the authors define hard and soft surfaces in terms of an anisotropic surface impedance, and propose to refer to such surfaces and their relatives by the common name "soft" surfaces.
Abstract: Transversely corrugated surfaces are widely used in the design of hybrid-mode horn antennas. The authors propose referring to such surfaces and their relatives by the common name 'soft' surfaces. The reasons for this are that (1) these surfaces have the same characteristics relative to electromagnetic waves as the so-called acoustically soft surfaces have relative to acoustic waves, i.e., that the density-of-power flux along the surface is zero at the surface, and that (2) there also exists so-called artificially hard surfaces in electromagnetics, along which the power flux has a maximum for any polarization of the electric field. The authors define hard and soft surfaces in terms of an anisotropic surface impedance. Characteristics and possible applications of soft and hard surface are described. >
63 citations
TL;DR: In this article, the authors show that the power radiated by the cluster feed is lost as spillover into space, and they show that this spillover may be reduced considerably by using hard horns as cluster elements.
Abstract: A major problem in many contoured-beam satellite antennas is that nearly half the power radiated by the cluster feed is lost as spillover into space. The authors show that this spillover may be reduced considerably by using hard horns as cluster elements. >
62 citations
TL;DR: In this paper, simple design curves for the efficiency reduction, the sidelobe levels, and the cross polarization caused by strut blockage are presented for a symmetrical reflector antenna, where the most significant IFR values for struts with circular cross section are calculated and plotted in a way which makes them easy to use as design curves.
Abstract: In a symmetrical reflector antenna the feed system and its support struts block the aperture and thereby deteriorate the radiation characteristics. Simple design curves are presented for the efficiency reduction, the sidelobe levels, and the cross polarization caused by strut blockage. The results are obtained from an analytical study that includes the induced field ratio (IFR) of the struts. The most significant IFR values for struts with circular cross section are calculated and plotted in a way which makes them easy to use as design curves. The use of the design curves is demonstrated by an example. >
57 citations
01 Oct 1988
TL;DR: In this paper, a reduction of forward scattering from struts has been achieved by forming the strut cross section into a rhombic shape and making the surface approximately "hard", both longitudinally corrugated and strip-coated surfaces are shown to give approximations to the desired boundary conditions.
Abstract: A reduction of forward scattering from struts has been achieved by forming the strut cross section into a rhombic shape and making the surface approximately "hard". Both longitudinally corrugated and strip-coated surfaces are shown to give approximations to the desired boundary conditions. The basic properties of these surfaces have been studied numerically, and the induced field ratios of two struts have been measured. For the polarization with initially strong scattering, a significant reduction is demonstrated. For the orthogonal polarization with initially weak scattering, an increase is observed. This increase can be reduced by an optimized design of the surface geometry.
9 citations
06 Jun 1988
TL;DR: In this paper, the synthesis of offset dual-reflector antennas is reduced to solving nondifferential equations, which is made possible by approximating a known solution for the geometrical optics (GO) field reflected from a surface, and using local parabolic expansions of the reflector surfaces.
Abstract: An approach is presented by which synthesis of offset dual-reflector antennas is reduced to solving nondifferential equations. This is made possible by approximating a known solution for the geometrical optics (GO) field reflected from a surface, and using local parabolic expansions of the reflector surfaces. The advantages of this approach are that the calculation is easy to carry out, the condition of low cross-polarization is included, and the question of existence clearly can be answered. The synthesis method can also readily be extended to the synthesis of multireflector antennas. >
8 citations
06 Jun 1988
TL;DR: In this paper, a transition region theory (TRT) code is described for dynamic ray field amplitude and polarization tracing. But the code is not applicable to the case of the radio observatory in Arecibo.
Abstract: The antenna of the radio observatory in Arecibo is currently fed by line feeds that correct for the spherical aberrations of the reflector. To improve the bandwidth and the sensitivity of the radiotelescope the line feeds will be replaced with a dual-reflector feed system. A computer code is described that is based on an efficient geometrical optics (GO) ray tracing technique. The code, called the TRT code, is related to the procedure of dynamic ray tracing used in seismics, which means that the complete complex ray field amplitude (and polarization for EM waves) is traced. The code also makes use of the paraxial-ray approximation, applied by considering each individual ray as an axis. In addition to the GO analysis, the code gives asymptotic information about the diffraction losses. This is obtained by the diffraction tracing techniques of the transition region theory (TRT). The characters of the TRT code are noted. >
4 citations
01 Oct 1988
TL;DR: In this paper, the authors present a method to improve the calculation of the directivity and the radiation pattern of a primary-fed reflector antenna, by including the contribution due to multiple reflections between the feed and the reflector.
Abstract: This paper presents a method to improve the calculation of the directivity and the radiation pattern of a primary-fed reflector antenna, by including the contribution due to multiple reflections between the feed and the reflector. These multiple reflections are controlled by introducing a feed scattering pattern, which is the scattered field from the feed when illuminated by a plane wave. The method is applied to a reflector with a self-supported dipole-feed, showing good agreement with both the measurements and a moment method solution of the complete antenna including the feed as well as the paraboloidal reflector. The results show that the multiple reflections may have stronger effect on the directivity and the cross-polar sidelobe level than the centre blockage has.
3 citations
01 Apr 1988
TL;DR: In this paper, the authors give an overview of the activity in the areas of reflector antennas and feeds in Norway since 1978, including cylindrical, symmetrical, spherical, offset, single and dual-reflectors, and primary dipole feeds.
Abstract: This article gives an overview of the activity in the areas of reflector antennas and feeds in Norway since 1978. The activity includes cylindrical, symmetrical, spherical, offset, single- and dual-reflectors, and primary dipole feeds, waveguide feeds, hybrid-mode feeds, lens feeds and microstrip antennas. The work has resulted in industrial applications and a number of articles in international journals.
3 citations