Cosmology

Abstract:

We describe the design and performance of an easy to machine horn which exhibits excellent beam circularity and low cross polarisation over a relatively large bandwidth. No grooves are machined into the horn walls but, alternatively, flare angle discontinuities are generated along the horn profile. In other words, the horns will have several flare angles or sections instead of one. For example, if the horn consists of two flare angles, it could then be considered as a conventional Potter horn. As can be seen below, even with this simple design, excellent radiation patterns can be obtained over 15% bandwidth. The bandwidth could be further increased by adding more subsections with 30% bandwidth obtained when the profile is based on 4 sections. The operation of the horn is based on generating higher order modes at the correct amplitude ratio and phase with respect to the incident TE11 mode in the circular waveguide, which is achieved by accurate determination of the magnitude and location of the flare steps. This in turn yields a field distribution at the horn aperture that has low sidelobes and cross polarization in the radiation pattern. A key component in the design package is the optimization software that searches for the correct magnitude and location of the flare discontinuities. We have generated a software package based on the combination of modal matching, genetic algorithm (GA) and simplex optimization. The genetic code is first used to locate the proximity of the global minimum. The set of parameters obtained are then used as a starting point for the simplex method, which refines the parameters to the required accuracy. We shall illustrate our method by showing radiation patterns using two and three step discontinuities and also patterns for a spline profiled horn based on work by other investigators who used different optimization techniques.