Graeme L. James

A smooth-walled spline-profile horn as an alternative to the corrugated horn for wide band millimeter-wave applications

At millimeter-wave frequencies, corrugated horns can be difficult and expensive to manufacture. As an alternative we present here the results of a theoretical and measurement study of a smooth-walled spline-profile horn for specific application in the 80-120 GHz band. While about 50% longer than its corrugated counterpart, the smooth-walled horn is shown to give improved performance across the band as well as being much easier to manufacture.

Diplexing feed assemblies for application to dual-reflector antennas

We investigate possible configurations for dual-band waveguide diplexing assemblies appropriate for use as feed systems for dual-reflector antennas. Specific applications are where the bands are well separated and, individually, have relatively wide bandwidths. Two crucial problems are addressed: the demanding bandwidth requirements of the feed horn and the subsequent means of diplexing the signals. We present results arising from the analysis of candidate systems and discuss a preferred option in detail.

Design of wide-band corrugated conical horns for Cassegrain antennas

Design procedures based on extensive theoretical and experimental investigations are given for hybrid-mode corrugated conical horns having near-constant beamwidth, low cross-polarized sidelobes and low reflection for continuous bandwidths up to 2.1:1. The design techniques are applicable for horn flare semi-angles to about 30\deg , which includes most feed horns in dual-reflector antennas.

Compact multimode horn with low sidelobes for global Earth coverage

A new multimode corrugated horn is described for full-Earth coverage from a geostationary satellite. The horn has low sidelobes, low cross polarization, and is compact. We outline the design of this horn and compare its performance with other circular horn types, including conventional single and multimode-corrugated horns and dielectric loaded horns. A design was fabricated and measured results are described for return loss, radiation patterns, and axial ratio. These measurements demonstrate excellent agreement with computer predictions using mode-matching software.

The designing, manufacturing, and testing of a dual-band feed system for the Parkes radio telescope

This paper presents the designing, manufacturing, and testing of a dual-band feed system for the Parkes radio telescope (Australia). The feed system consists of a coaxial horn and associated feed components to operate in the 648-712 MHz and 2.6-3.6 GHz frequency bands. The manufacturing of such a feed system was challenging, and we present the innovative solutions that were devised to fabricate the different parts of the feed system. Preliminary measurements indicate that the overall system, feed and reflector, is working to operational expectations, and valuable scientific results have already been obtained using the simultaneous dual-frequency capability.

TE 11 -to-HE 11 mode converters for small angle corrugated horns

A theoretical and experimental study of mode conversion from the transverse electric (TE 11 ) mode in a circular waveguide to the HE 11 hybrid mode in a small angle conical corrugated horn is given. Mode conversion is achieved through a transition section where the slots are either ring-loaded or are conventional slots of varying depth. Using varying depth slots the optimum design gives a return loss exceeding 30 dB over a 1.45 bandwidth ratio, with the low frequency limit determined by the deterioration in return loss, and the upper frequency limit determined by the excitation of excessive levels of the unwanted EH 12 hybrid mode. Using ring-loaded slots a bandwidth ratio of 1.55 is possible, increasing to at least 2.0, if the small amount of of EH 12 mode generated (being an order of magnitude less than the case using varying depth slots) is acceptable.

Millimetre-wave antenna and propagation studies for indoor wireless LANs

The combination of increased portability and increased computing power is placing new demands on interconnects with other such new computer systems and existing networks. One possible way of providing the required interconnections while maintaining portability is through wireless systems. Relatively low bit-rate systems are already available in the market place, and faster, second-generation systems are under development. This paper outlines work in progress at CSIRO on millimetre-wave antennas and propagation relating to wireless local area network (WLAN) systems operating at frequencies in the 40 to 60 GHz band for intra-office communication. The basic arrangement for such systems involves a hub antenna, located possibly in the ceiling, and a number of roamable antennas located on desks throughout the room, within a radius of about 20m of the hub. Signals transmitted to and from the antennas are subject to considerable multi-path interference and, whilst this can limit the system performance, it can be used to overcome the effect of obstructions in the direct path. It is apparent that to optimize WLAN performance it is important to understand propagation effects in rooms and to develop antennas whose characteristics match the overall requirements, including cost.<<ETX>>

Compact low-sidelobe corrugated horn for global-Earth coverage

A new corrugated horn is described for providing full-Earth coverage from a geostationary satellite. The horn has low-sidelobes, low cross-polarization and is very compact. We outline the design of this horn and describe its performance giving theoretical and measured results for return loss and radiation patterns.

A dual-band feed system for the Parkes radio telescope

A dual-band, dual-polarisation, coaxial receiver system for 10 cm and 50 cm wavelengths is being designed and constructed for the Parkes radio telescope. While the primary motivation is to provide a receiver system optimised for pulsar observations, the feed system will also be used for other wideband continuum observations, such as the 9 cm transition of CH and various recombination lines.

Optimized Spline-Profile Smooth-Walled Tri-Band 20/30/44-GHz Horns

A smooth-walled spline-profile approach has been used to design two examples of easily constructed tri-band 20/30/44 GHz horns. Surprisingly good results were obtained with such a simple configuration. The radiation patterns of the horns have low sidelobes and acceptable cross-polarization levels within each band for application to a very small aperture terminal (VSAT) mobile antenna link.