John S. Kot

RADAR CROSS-SECTION STUDIES OF SPHERICAL LENS REFLECTORS

The reflectivity of a Spherical Lens Reflector is investigated. The scattering of an electromagnetic plane wave by a Spherical Lens Reflector is treated as a classical boundary value problem for Maxwell’s equations. No restrictions are imposed on the electrical size of reflectors and the angular size of the metallic spherical cap. The competitiveness of the Spherical Lens Reflector against the Luneberg Lens Reflector is demonstrated. It has been found that Spherical Lens Reflectors with relative dielectric constant in the range 3.4 ≤ er ≤ 3.7 possess better spectral performance than 3or 5-layer Luneberg Lens Reflectors in a wide frequency range.

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>>

Australian activities in microwave links for wireless LANs

A program centered at the CSIRO Division of Radiophysics in Australia aims to develop third-generation wireless systems with capacities on the order of 100 Mb/s in a cell. The authors discuss some of the issues relating to the design of millimeter-wave antennas and transceiver MMICs (monolithic microwave integrated circuits) for operation at frequencies near the 60-GHz ISM (industrial scientific, and medical) band. Components in this wavelength range have traditionally suffered from the high cost of labor-intensive manufacture, which has acted as a major impediment to commercial utilization. Successful implementation of this wireless local area network (LAN) program will require the development of multifunctional MMICs combined with sophisticated planar antennas in low-cost, easily assembled packages.<<ETX>>

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.

Analysing radiation from a cylindrical-rectangular microstrip patch antenna loaded with a superstrate and an air gap, using the electric surface current model

This paper presents an analysis of radiation from a cylindrical-rectangular microstrip patch antenna loaded with a superstrate and an air gap between the substrate and the superstrate, using the full-wave approach and the electric surface current model. Numerical results are presented in the form of normalized radiation patterns for various thicknesses of the air gap and also for superstrates made of lossy dielectric material, to show the effects of these on the radiation from the antenna.

The Luneburg lens as a radio telescope element

Serious consideration of the scientific objectives for the next generation decimeter radio telescope includes, as a major objective, the desire to study interstellar hydrogen in the early universe occurring at large red-shifts. This has led to the proposal for a Square Kilometre Array (SKA). Among the primary specifications are large collecting area (the square kilometre relates to the effective collecting area of the telescope at 1.4 GHz), wide frequency coverage (200 MHz to 2 GHz minimum), large dynamic range, full sky coverage and the possibility of forming multiple simultaneous beams on the sky. A lens can have both a wide field-of-view and a high aperture efficiency. Indeed, only a lens appears to offer the possibility of maintaining a constant collecting area for all viewing directions and thereby allowing a multiple beam capability through the use of a fixed focal plane array or lightweight movable feeds. We propose the consideration of a Luneburg lens to meet the requirements of the antenna element for the SKA.

An Integrated Wideband Circularly-Polarized 60 GHz Array Antenna with Low Axial-Ratio

An integrated, circularly-polarized antenna comprising an annular slot and hybrid feed network fabricated on a standard liquid crystal polymer (LCP) substrate is described. The antenna is designed to operate in the WPAN band around 60 GHz. Modeled results for a single element and a 2x2 array are presented. The antenna bandwidth is sufficient to cover the entire WPAN band, and the array antenna has very low axial ratio, better than 0.3 dB across the band.

A Spherical Lens for the SKA

Spherical refracting lenses based upon the Luneburg lens offer unique capabilities for radioastronomy, but the large diameter of lens required for the Square Kilometre Array (SKA) means that traditional lens materials are either too dense or too lossy. We are investigating a composite dielectric that theoretically offers extremely low loss and low density, and is suitable for low-cost mass production. We describe our progress towards realising this material and demonstrating the manufacturing concept, via the manufacture and testing of a small (0.9 m) spherical lens.

The Analysis of 3D Model Characterization and its Impact on the Accuracy of Scattering Calculations

When employing computational methods for solving problems in electromagnetic scattering the resulting solutions are strongly determined by the geometry of the scatterer. Careful consideration must therefore be given to the computational geometry used in representing the scatterer. Here we show that the solution for a problem as simple as plane wave scattering ofi a PEC sphere is sensitive to the computational geometry used to represent the sphere. We show this by implementing 4 higher-order computational geometry schemes over 3 difierent tessellations resulting in 45 difierent representations of the sphere. Two methods for solving the scattering problem are implemented: the boundary-element method (BEM) based on the MFIE, and the physical optics (PO) method. Results are compared and insights are obtained into the performance of the various schemes to model surfaces accurately and e-ciently. The comparison of the

Wideband dual polarized line feed development for a cylindrical reflector radio telescope

A new wideband dual polarized line feed element for a cylindrical reflector radio telescope has been presented. A novel feeding arrangement using microstrip baluns reduces element cost and losses compared to dual polarized dipole designs using hybrid coupler feeds. An 8-element line feed was simulated, constructed and measured for array radiation performance across a 1.57:1 frequency range, with good agreement between simulation and measurement. Beam equalization for both polarizations in the transverse plane was obtained using channels placed beside the elements. Cross-polar levels in the transverse plane patterns are shown to increase with scanning angle. Element patterns in the longitudinal plane, for both polarizations, show excellent polarization purity for wide scan angles. Implementation of the line feed at the MOST (Molonglo observatory synthesis telescope) will demonstrate a world first in polarimetric imaging using a cylindrical reflector radio telescope.