Kieran Greene

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.

Terahertz imaging at 77 K

Terahertz (THz) technology is receiving increasing attention around the world due to its important potential in many application areas. Novel compact solid-state sources and detectors are being sought for?THz radiation and detection. We report the realization of a?THz imager based on a high- Tc superconducting (HTS) Josephson detector working above liquid nitrogen temperature (77?K). The detector, made of a YBa2Cu3O7?x (YBCO) step-edge Josephson junction, is coupled to a thin-film ring-slot antenna and a hemispheric silicon lens. Images of high visual quality are obtained which demonstrate unique properties of?THz radiation such as the sensitivity to water content and the ability to penetrate packaging materials. The results should stimulate further research leading to the development of a HTS superconducting?THz imaging system.

Development of a Terahertz Imaging System

This paper introduces work being conducted by the authors towards developing terahertz (THz) imaging technologies. Specifically this paper addresses two topics: the development and implementation of a THz imaging system, and design of a THz detector. The THz imaging system has been implemented to allow exploration across a broad range of applications. An overview and design of this system are presented, along with early images acquired with the system. A high temperature superconducting device capable of detection at THz frequencies is being designed. As development of this detector is at an early stage simulated detector performance results are given; however, it is expected that detector results will be presented at the conference.

Microwave radar for detection of resin defects in Pinus elliottii Engelm var elliottii

Abstract Surface penetrating microwave radar is identified as a low-cost, reliable, portable, and safe means of detecting resin defects in plantation-grown pine logs. This new method of non-destructively testing logs has the potential to be applied at several intervention points in the value chain, including on standing trees, fallen stems, and merchandised logs either in the forest or in the mill. Results clearly distinguish resin-affected logs from unaffected logs, even in logs of high moisture content.

A wide-band prime-focus horn for low-noise receiver applications

A horn suitable for a prime-focus antenna requiring low cross polarization, wide bandwidth, and low spillover is described. The design is particularly suited for low-noise applications such as high-quality satellite earth-station antennas and radio telescopes. The horn has a return loss substantially better than 20 dB, a cross polar sidelobe level better than -20 dB, a beamwidth variation of 40% and negligible phase center shift. >

A 500-700 GHz system for exploring the THz frequency regime

The CSIRO ICT Centre has recently completed a terahertz demonstrator with the aim of exploring applications in the 500-700 GHz range. The system is capable of transmission measurements through samples, and simple modulation experiments. Further work towards realizing detection by arrays of superconducting detectors is being pursued. This paper describes the design choices and implementation of the terahertz system, discusses recent results and future directions.

Upgrade of an existing earth station for commercial and military applications using a new Ka-band feed system

This paper describes a Ka-band feed system capable of covering the full commercial and military frequency allocations (19.2 to 21.2 GHz for downlink and 29.0 to 31.0 GHz for uplink). The feed offers both right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP) in the transmit and receive frequency bands, making it suitable for installations accessing a number of Ka-band satellites. The feed was designed for an upgrade of an existing Ku-band facility.

Quarter-sphere Luneburg lens scanning antenna

Scanning properties of a quarter-sphere Luneburg lens with two backing ground planes are evaluated. The main beam of the antenna is scanned by rotating the feed antenna, as in a full or a hemispherical lens antennas. Since only one quarter of the lens is used the weight of the antenna is halved compared to a hemispherical lens. This reduction is achieved at the expense of the scanning range of the antenna. Simulated results for a small quarter-sphere two-layer lens operating at 20 GHz are presented, showing that scanning loss of less than 0.5 dB may be achieved in the range of ±50° in the azimuth plane and ±25° in the elevation plane.

Reduction of the grating lobes in Luneburg lens arrays

Mobile satellite communication systems suitable for installation on moving vehicles are increasingly in demand [1]-[3]. One of the main requirements for such systems is low-profile in order to prevent intolerable drag and air-stream turbulence. A low profile Ku-band antenna system based on a four-element Luneburg lens array (LLA) was presented in [3] where the reduction in height is achieved by using a ground plane and by increasing the number of elements at the expense of increased diameter of the array. However, using an array of elements has an inherent problem of grating lobes [4]. This problem is particularly difficult in an array of lenses since the minimum array spacing is limited by the lens size and generally it is of the order of several wavelengths. High grating lobes in the radiation pattern limit the usefulness of the lens array and their reduction is critical. So far, the results for the expected grating lobes in an array of Luneburg lenses have not been reported in the literature. Our aim is to study the grating lobes in a LLA as a function of the number of lenses in the array and also as a function of the spacing between the lenses. We present simulated results for the radiation patterns of two arrays using three and four Luneburg lenses, respectively, and show how removing part of the outer shells of the Luneburg lens and decreasing the element spacing can reduce the grating lobe level.