Nasiha Nikolic

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.

Terahertz imaging using a high-Tc superconducting Josephson junction detector

A high-Tc superconducting (HTS) detector based on a YBa2Cu3O7−x (YBCO) step-edge Josephson junction has been developed and applied to terahertz (THz) detection. The detector was coupled to a ring-slot antenna designed for operation at 600 GHz, and used for THz imaging. The results suggest that the characteristic voltage and frequency of our HTS step-edge junctions can be readily optimized for the chosen THz frequency range at easily achievable temperatures. The images also clearly demonstrate some of the unique properties of THz radiation, including the sensitivity to water content and the ability to penetrate packaging materials. (Some figures in this article are in colour only in the electronic version)

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.

Printed quasi-Yagi antenna with folded dipole driver

Printed quasi-Yagi antennas [1] have been used in a number of applications requiring broad-band planar end-fire antennas. So far they have been mostly realized on high dielectric constant substrates with moderate thickness in order to excite the TE0 surface wave along the dielectric substrate. An alternative design of a printed Yagi-Uda antenna, developed on a low dielectric constant material, was presented in [2]. In this design, an additional director and a reflector were used to increase the gain of the antenna. However the achieved bandwidth of the antenna is quite narrow (about 3–4%) compared to the bandwidth of a quasi-Yagi antenna fabricated on a high dielectric constant substrate [1]. Another disadvantage of a conventional quasi-Yagi antenna fabricated on a low dielectric permittivity substrate is that the length of the driver is increased and it is difficult to achieve 0.5 λ0 spacing between the elements required for scanning arrays, where λ0 corresponds to a free-space wavelength at the center frequency of the antenna.

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.

A dual-polarised wideband planar array for X-band synthetic aperture radar

This paper describes the design and performance of a wideband planar array panel for use in a dual linear-polarisation antenna for the Australian Defence Science and Technology Organisation (DSTO) Ingara X-band airborne synthetic aperture radar (SAR). The final array aperture is approximately 1200 mm by 200 mm and comprises 192 dual-fed microstrip patch elements divided into three panels, each panel with an integrated microstrip feed network. To accommodate high power operation, a coaxial power distribution network is used to feed the panels. The primary objective of the design was to achieve on-axis cross-polarisation radiation in each polarisation at least 25 dB below the co-polarised radiation over a 600 MHz bandwidth.

Demonstration of Adaptive Analogue Beam Forming in the E-Band

In this paper, we report the test results of a small-scale prototype that implements an analogue-beam-formed phased antenna array in the E-band. A four-channel dual-conversion receive RF module for 71~76 ㎓ frequency band has been developed and integrated with a linear end-fire antenna array. Measured performance is very close to the simulated results. An ad-hoc wireless communication system has also been demonstrated. Low BER was measured for an 8PSK data stream at 1.5 Gbps with the receive array beam formed in the direction of arrival of the transmitted signal. To our knowledge this is the first steerable antenna array reported to date in the E-band.

A High-Gain Dual-Band EBG Resonator Antenna with Circular Polarization

A dual-band circularly polarized (CP) electromagnatic band-gap (EBG) resonator antenna (ERA) is presented. The antenna employs an all-dielectric superstructure, which consists of two identical unprinted dielectric slabs, and a dual-band corner-truncated patch feed. A prototype antenna is fabricated and tested using a superstructure made out of 3.175-mm-thick Rogers TMM10 material. Measured peak gains are 16.1 dBic [left-hand circular polarization (LHCP)] and 16.2 dBic [right-hand circular polarization (RHCP)], measured radiation efficiencies are 93% and 91%, and the boresight axial ratios are 1.9 and 1.5 dB at 9.65 and 11.75 GHz, respectively. This dual-band antenna is easy to fabricate, making it suitable for high-gain low-cost CP applications.