Current requirements on microwave reflector antennas for modern communication and radar systems impose stringent specification on impedance match, sidelobe level and polarisation purity. Corrugated horns are widely used as primary feeds for such systems due to their excellent radiation characteristics which can be maintained over a relatively wide bandwidth or over multiple widely separated frequency bands. The fundamental theory of corrugated horns, based on the surface impedance concept, is well established and commonly used in the design procedure. However, the impedance model fails to predict accurately the return loss and cross-polar characteristics. The engineer is then left with the problem of optimising, at least partly, the performance of the horn empirically through a measurement and modification procedure. This is ineffective in terms of both development time and cost.The objective of this paper is to demonstrate that a fully computer-optimised design and analysis procedure for circular corrugated horns comprising radial slots is realised in practice. In a previous paper (1) the modular analysis technique was verified for the fundamental TE 11 /HEg1 mode using a profiled wide-angle corrugated horn with only seven axial slots. In the application presented here the technique is extended and verified for multi-slot corrugated horns together with the inclusion of higher order tracking modes (TE21/HE21 and TM01/E02).
COMPUTER-AIDED ANALYSIS AND DESIGNThe modular analysis concept is applied for the design of circular corrugated horns.In this approach the corrugation boundary which may comprise either (ring-loaded) radial or axial slots is decomposed into basic modules as shown in Figure 1. The scattering matrix of each module is determined separately and, by cascading module by module, the scattering matrix of the entire horn can be obtained. The radiated field and the total field across the aperture can then be calculated in terms of the incident modes in the aperture by means of an integral equation method (2) which can also include flange effects. Once the aperture field is known, the reflection at the horn throat can be computed from the scattering matrix description of the entire horn. This modular analysis concept has the advantage that it incorporates all the geometrical parameters of the horn and does not impose any restrictions, except that the semi-flare angle should not exceed 90 . Thus, it offers the possibility to investigate corrugated horns with arbitrary surface profiles and arbitrary dimensions of the slots and ridges in order to meet particular design constraints, or to best suit manufacturing convenience. It also provides for a parametric study to optimise the corrugation geometry or for a tolerance analysis of the horn parameters. Many other structures can also be modelled such as TE mode impedance transformers and tapers in circular waveguide, TE11/HE11 moAe converters, choked flange feeds, radial line chokes and cavity filters. 228
APPLICATIONThe corrugated horn to be described in t...
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