Although used for some decades, the offset-parabolicreflector antenna's electrical properties and performance were not accurately modeled and optimized until the 1960's. This paper reviews, in a tutorial fashion, the state of the art of this important antenna for readers who are not necessarily experts in antenna theory and technology. After a discussion of fundamentals, the performances of both single- and double-reflector configurations are treated and compared, and practical primary feeds are described. Comments are given on the present status of analysis and design and on problems to be solved.

Offset-parabolic-reflector antennas: A review

Cet article fournit une vue d’ensemble didactique sur differentes configurations a un et a deux reflecteurs. L’auteur presente d’abord quelques methodes utilisees pour calculer les champs vectoriels rayonnes et en discuter la validite. Il decrit une methode analytique simple dans l’approximation de l’optique geometrique physique. Il compare les caracteristiques radioelectriques theoriques de la configuration a un seul reflecteur avec des resultats experimentaux en soulignant les problemes particuliers dus au type de polarisation et aux dimensions du reflecteur et en envisageant quelques applications pratiques telles que faisceaux multiples, faisceaux conformes, poursuite monopulsee et faibles lobes lateraux. L’auteur decrit des sources primaires et discute de la notion de source adaptee en mettant en evidence l’adaptation de la source primaire au champ incident dans le plan focal du reflecteur. Les avantages et les inconvenients des antennes a deux reflecteurs et a source decalee sont discutes en insistant sur la configuration Cassegrain ouverte et sur la configuration optimisee a double decalage (reflecteur secondaire et source primaire) qui permet, en principe, d’eviter l’obstruction par le reflecteur secondaire et d’obtenir de faibles niveaux en polarisation croisee.

Offset parabolic reflector antennas

The response of reflector antennas to out-of-band frequencies has been analyzed using physical optics. A simple approximate expression has been obtained for the effective aperture, and this expression yields both the receiving pattern and the frequency dependence of the on-axis gain. The theory has been compared with published out-of-band measurements, and the pattern agreement is good, but the measured gain falls below the theory. This discrepancy is caused by mismatch loss in the coax-to-waveguide adapter.

Out-of-Band Response of Reflector Antennas

Out-of-band response of reflector antennas

We propose a tensor product derivative matching (TPDM) method to restore the accuracy of high-order finite difference time-domain (FDTD) schemes of computational electromagnetics (CEM) with material interfaces in two spatial dimensions (2D). By making use of fictitious points, the TPDM method locally enforces the physical-jump conditions at material interfaces in a preprocessing stage to arbitrarily high orders of accuracy in principle, based on a structured grid. The proposed method encompasses a variety of schemes of different orders in a single code. In fact, numerical orders from 2 to near 16 are confirmed in the present study. To the best of our knowledge, such high orders have not been reported in the literature for CEM problems involving material interfaces. The limitation and applicability of the present scheme are also analyzed in detail. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 69–77, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20378

Tensor product derivative matching for wave propagation in inhomogeneous media

An analysis which provides the electric field distribution in the focal region of an offset parabolic reflector as a function of small scan angle has been performed. Formulae which predict both the principal and cross polarized fields have been obtained. These formulae are relatively simple and compact, provide a useful design tool, and allow efficient computer calculation. The results obtained from these formulae compare favorably with results obtained by other authors.

A. Valentino

Papers

Fields in the focal region of offset parabolic antennas