Bevan Bates

Automatic Target Recognition by Means of Polarimetric ISAR Images and Neural Networks

Inverse synthetic aperture radar (ISAR) images are often used for classifying and recognizing targets. Moreover, the use of fully polarimetric ISAR (Pol-ISAR) images enhances classification capabilities. In this paper, the authors propose a novel automatic target recognition (ATR) technique based on the use of fully Pol-ISAR images and neural networks (NNs). In order to reduce the amount of data processed by the classifier, the brightest scattering centers are first extracted by means of the Pol-CLEAN technique, and then, their scattering matrices are decomposed using Camerons decomposition. A classifier based on the use of multilayer perceptron NN that makes use of the features extracted from the Pol-ISAR images is then implemented. A proof-of-concept test is performed on real data acquired during a controlled experiment in an anechoic chamber.

Electrically Tuned Microwave Devices Using Liquid Crystal Technology

An overview of liquid crystal technology for microwave and millimeter-wave frequencies is presented. The potential of liquid crystals as reconfigurable materials arises from their ability for continuous tuning with low power consumption, transparency, and possible integration with printed and flexible circuit technologies. This paper describes physical theory and fundamental electrical properties arising from the anisotropy of liquid crystals and overviews selected realized liquid crystal devices, throughout four main categories: resonators and filters, phase shifters and delay lines, antennas, and, finally, frequency-selective surfaces and metamaterials.

Clean technique for polarimetric ISAR

Inverse synthetic aperture radar (ISAR) images are often used for classifying and recognising targets. To reduce the amount of data processed by the classifier, scattering centres are extracted from the ISAR image and used for classifying and recognising targets. This paper addresses the problem of estimating the position and the scattering vector of target scattering centres from polarimetric ISAR images. The proposed technique is obtained by extending the CLEAN technique, which was introduced in radar imaging for extracting scattering centres from single-polarisation ISAR images. The effectiveness of the proposed algorithm, namely, the Polarimetric CLEAN (Pol-CLEAN) is tested on simulated and real data.

Tunable electric-LC resonators using liquid crystal

A concept of tunable electric-LC (ELC) resonators is presented in this work. The voltage-controlled tunability is achieved by using liquid crystal in a micro-fluidic channel running through the central capacitive gaps. To attain the largest tunability, the structure is optimized through a parametric analysis using full-wave electromagnetic simulations. The simulation results predict a 6% continuous frequency tuning for this ELC resonator around the frequency of 4.5 GHz. The achieved results demonstrate the possibility of using these ELC resonators in an array to form a tunable frequency selective surfaces (FSS). The principle can be scaled for operation at higher microwave frequencies, where the dissipation of liquid crystal is low.

Image contrast and entropy based autofocusing for polarimetric ISAR

In recent studies the possibility of extending autofocusing techniques to fully polarimetric ISAR systems has been proposed. The image contrast and entropy based autofocusing techniques have been proposed in the last decade as some of the most common techniques for obtaining well focused single polarisation ISAR images. In this paper, the two techniques are extended and applied to fully polarimetric ISAR data. A performance analysis is then provided and compared to single polarisation ISAR using real data.

WREN: A weather radar experimental network

Limitations to current long range weather radars include reduced coverage of the lower atmosphere, coarse cross range resolution and coarse temporal resolution due to the mechanical scanning. A proposed network of low cost, short range digital radars for monitoring hydrometeor phenomena is described and its potential benefit in providing lower atmospheric coverage is discussed. The benefits of replacing the scanning antenna at each node of the network with a phased array are also discussed.

A 2 GHz Polypyrrole microstrip patch antenna on Plexiglas ™ substrate

A Microstrip Patch Antenna (MPA) has been fabricated using a Conducting Polymer (CP), Polypyrrole (PPy) as radiating patch on a transparent 3mm thick Plexiglas™ substrate. The bulk DC conductivity of the PPy patch is 2000 S/m and its thickness 120 µm. The MPA was designed for operating at 2 GHz. A similar antenna with Copper (Cu) patch on Plexiglas™ was also fabricated for validating the simulation of PPy antenna and comparing its performance. The results show that the PPy antenna reaches a gain of 5.01 dB at 2.18 GHz as against 6.26 dB at 2.2 GHz for a corresponding Cu patch antenna. The conduction efficiency of Cu-patch antenna is around 80% while that of PPy-patch antenna is around 60%. The results suggest that it might be possible to use CPs in other passive microwave circuit applications.

Polarimetric phase gradient autofocus

In the past decade the use of fully polarimetric SAR (polSAR) systems has increased significantly due to their effectiveness in target classification and detection applications. While polSAR imagery has been extensively used to distinguish between different scattering mechanisms in a scene, there has been a lack of research in the exploitation of polarimetry to assist in image formation and in particular autofocus for fine resolution SAR. In this paper an extension of the phase gradient algorithm (PGA) for polSAR imaging is proposed and its effectiveness is tested on simulated and real data.

A multi-layered tunable stepped-impedance resonator for liquid crystal characterization

The characterization of a tunable band-pass filter based on stepped-impedance resonator (SIR) is presented in this work. The designed filter uses a half-wavelength resonator patch above a multi-layer substrate, with liquid crystal as its central layer, making it continuously tunable at frequencies around S-band. Two liquid crystal samples are considered for three different approaches: lumped-element circuit simulation, full-wave electromagnetic simulations and prototype measurements. The results demonstrate the possibility of using a simple lumped-element circuit simulation for rapid calculation of the performances of liquid crystal devices at microwave frequencies.

Development of a baseband signal ATI-SAR simulator for ground moving target indication

Along-track SAR interferometry has long been used to measure ocean surface currents with small velocities. There is a significant potential to employ this technique to detect slow ground moving targets with small radar cross-sections. In this paper, we present the development of a baseband signal simulator on ground moving target indication with along-track SAR interferometry. We summarize current state-of-the-art along-track SAR interferometry techniques and algorithm developments for ground moving target detection, and consider the case of an airborne SAR operated in the stripmap mode. And then we propose to investigate and develop advanced techniques for potential civilian and military applications in Australia.