A prototype of the helicon double layer thruster (HDLT) is designed and manufactured. Initial tests with the thruster mounted on a small vacuum chamber (pumping speed of 700 1 · s -1 ) show successful operation in xenon with the formation of the double layer which generates a low divergence ion beam, which is the source of thrust. The prototype is subsequently inserted inside a much larger space simulation chamber (pumping speed of 7000 1 · s -1 ). A high-density blue mode is found when increasing the RF power above 380 W, and measurements with a Langmuir probe give an estimated density of 10 12 cm -3 in the thruster. An image of the HDLT operating in the high-density blue mode is presented. © 2008 IEEE.

For over a decade the Institute for Telecommunications Research (ITR) has built a reputation for innovation in satellite and wireless communications. With dramatic changes to the Australian and international landscape, driven by privatisation and the emergence of a new industry structure and by the rapid uptake of readily available wireless and mobile technologies, sustaining telecommunications research at a technology level in Australia is getting harder and harder. This paper explores ITR's mission and looks at the conditions that have allowed it to prosper.

A hybrid procedure that combines the least squares finite element method (LSFEM) and the transfinite element method is applied to the analysis of multiport Rotman lenses. The LSFEM is employed to build a functional based on the L2-norm of the residuals of the full first-order Maxwell equations governing the electromagnetic fields in the structure. Because the full first-order Maxwell equations are solved, the method is free from spurious solutions. The transfinite element method is used to transfer the exterior conditions in the port regions to the interior region. The method is applied to a Rotman lens to determine the field distribution in the lens and the scattering parameters. Measured results for a microstrip Rotman lens with nine beam ports and eight array ports show good agreement with theoretical predictions.

A hybrid procedure is presented that combines the least-squares finite element method (LSFEM) and the transfinite element method for analyzing microwave circuits. The benefits of the LSFEM for modelling the interior region of the circuit are combined with those of the transfinite element method to effectively couple the fields to semi-infinite port regions where the scattering parameters of the circuit are to be determined. The validity and efficiency of this new technique are demonstrated.

A Ka-band transponder system has been designed for the microsatellite FedSat-1. The transponder will allow propagation and communication experiments over the three year lifetime of the satellite, supporting the further development of space systems and the modeling of lifetime performance of the Ka-band monolithic microwave integrated circuit (MMIC) components. The transponder will provide a means of testing the benefits of small, low power and low cost satellites.

This paper presents an overview of monolithic millimetre-wave integrated antenna design and related considerations, relevant to wireless local area networks. Monolithic integration of antenna elements avoids feed-line connectors and as a consequence yields more reliable and cost-effective assemblies. Research on designs that takes account of technology constraints and system requirements leads to preferred elements and architectural features of arrays for fully integrated front-end modules. The potential for optical signal distribution and optical control of millimetre-wave antenna beam formation is briefly described, with particular emphasis on the aspects of technology and fabrication common to both optical and millimetre-wave integrated circuits and which may facilitate interconnection between wired and wireless data networks.

Reliable and cost-effective packaging of monolithic microwave integrated circuits (MMIC's) is an important aspect of the design of phased array systems. At millimeter wave-lengths, where small dimensions make machining and assembly a complex matter, the interconnections between the modules housing the MMIC components and the antenna elements are a source of unreliability as well as a potential problem in terms of electromagnetic losses. One solution involves the integration of antenna elements onto the MMIC chips. This paper addresses the issues involved in packaging and housing MMIC chips with integrated antenna elements and presents some insights into the electromagnetic design of such packages. © 1995, IEEE

An electric field integral equation method for the analysis of three-dimensional composite conducting and dielectric structures is applied to a metal strip antenna on an electrically thick dielectric substrate of finite size in a uniform infinite array environment An efficient solution is found using the method of moments. Metal strip folded dipole antennas are analyzed both with and without a coplanar strip feed line, and the effects of the substrate and feed line are investigated. A technique for minimizing the effect of feed line scattering is presented, and arrays of these elements are shown to be capable of good scanning performance over a wide range of beam-steer angles. A phased array simulator experiment is described and the measured results show good agreement with those obtained by analysis. The class of antenna elements studied may be fabricated using monolithic microwave integrated circuit (MMIC) technology, and the analysis described in this paper illustrates the expected characteristics for millimeter-wavelength phased arrays of this type. © 1993 IEEE

An analysis of the mutual coupling between metal strip antennas which are contiguous with the ends of finite size, electrically thick dielectric substrates is outlined. Such antennas have been proposed as useful monolithic microwave integrated circuit (MMIC) antennas for Millimeter Wavelength applications. The analysis presented here is verified experimentally, and the results are applied to three-element arrays of metal strip folded dipoles with coplanar strip feed lines. The effect of the electrically thick, finite size dielectric substrates on the mutual coupling between elements of the arrays is described. © 1993 IEEE

A solution to the problem of radiation by a narrow metal strip antenna contiguous with the edge of a dielectric substrate is presented where the substrate has parameters such that its electrical thickness is appreciable. Such an antenna may be useful at millimeter wavelengths as an integrated phased array element forming a part of a monolithic microwave integrated circuit (MMIC). A suitable geometry for this application is illustrated and an efficient computational procedure developed. Comparisons with experimental results for the input impedance and far-field radiation show excellent agreement. The influence of the dielectric substrate on the performance of an antenna designed to operate at approximately 60 GHz is then discussed. Two examples, the first involving the analysis of a co-planar strip transmission line fed antenna and the second involving impedance matching and control of cross-polarized radiation using a folded strip dipole, are given to illustrate practical applications of the analytical method to design problems. © 1992 IEEE

The Helicon Double Layer Thruster is a new type of magneto-plasma thruster which combines the helicon technology for an efficient coupling of the electrical power to the plasma and a current-free double layer (formed spontaneously in the physical and magnetic nozzle of the thruster) for an optimized acceleration of the plasma ions. A large area, low divergence supersonic ion beam (the source of thrust) is measured in the nozzle for various propellants (xenon, argon and hydrogen). In addition to the scalability in geometry and electrical power, the simplicity, the absence of any moving parts, electrodes, or neutralizer give the HDLT an infinite lifetime.

The study aimed to analyse the performance of a focal plane array in combination with reflector systems of small F/D parameter (F/D<0.5). Geometries of 2 Radio Telescope reflector antennas (WSRT and PARKES) were used while the array feed was optimised for the WSRT reflector antenna only. Synthesis of the array feed was done with a dense Vivaldi array operating in a frequency band of 2-5GHz. Conjugate field matching (CFM) in the focal area of the reflector was applied to determine the required number of array elements, arrangement and the optimal excitation coefficients. To verify a theoretical model, measurements of the array feed were carried out with a near-field scanner. The experimental results were used as an input source in the GRASP simulator to predict the far-field patterns of the WSRT and PARKES reflector antennas.

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.

This paper addresses the problem of ship wake detection and analysis at low grazing angles. Specifically, we examine the spatial distribution of the characteristic polarimetric signatures of the sea surface in and around the wakes of a pilot boat. The received signals were range-processed and polarimetrically decomposed to yield the characteristic polarisation states. Inspection of the locations of these states revealed that the polarisation signatures were highly non-uniformly distributed in the spatial domain, as expected, with interesting features attributable to nonlinear effects. Focusing on the cross-polar nulls, we found that the corresponding eigenvector distribution made a strong transition as one moved from the wake region to the surrounding sea. By defining appropriate scalar quantities we were able to identify wake and clutter regions. The results suggest that exploitation of the coherent polarisation domain may significantly enhance wake feature extraction and discrimination.

The design and performance of a wideband planar array panel for X-band synthetic aperture radar (SAR) was discussed. The antenna architecture shows a final array aperture of 1200 mm by 200 mm and comprises 192 dual-fed microstrip patch elements divided into three panels. Each panel comprises of an integrated microstrip feed network fed by a coaxial power distribution network. Measurements on the array panels show a low cross polarization maintained across a wide bandwidth. The array is suitable for SAR polarimetry applications.

This paper describes two experiments conducted using the DSTO mobile high resolution radar facility to observe wave breaking events induced by ship wakes. In the first experiment high resolution polarimetric range profiles of the wake produced by a displacement hull vessel were recorded at X and Ku band frequencies. Periodic transient enhancements were observed, generated by wave breaking events precipitated by the superposition of the dominant wake components with the crests of the incoming swell. In order to identify the induced wave breaking events unambiguously, the measurements were carried out for ship headings directly into and directly opposed to the prevailing waves. Clear confirmation of the proposed mechanism was thus demonstrated. The second experiment employed a planing hull vessel. Because of the high speed of this ship, the measurement geometry was changed to set one of the diverging wake arms perpendicular to the radar beam. High resolution polarimetric range profiles were then recorded at X and Ku band frequencies.

The consideration of a Luneburg lens to meet the requirements of the antenna element for the square kilometer array (SKA) is proposed. The benefits of this concept for SKA are detailed.

An antenna element based on the Luneburg lens best meets the electromagnetic requirements of the Square kilometer array. There are a number of practical difficulties in implementing such an antenna element. Means of overcoming them are suggested. Initial calculations on the electromagnetic performance of Luneburg lens are presented. The Luneburg lens allows perfect focusing from all feed positions on the surface. In Luneburg lens multiple beams are achieved without the need of a phased array. Light-weight isotropic artificial dielectrics are developed to allow analytical tools to design a complete antenna element.

Advanced Ka-band space qualified hardware has been developed for communications and propagation experiments with low earth orbiting (LEO) satellite systems as part of the Co-operative Research Centre for Satellite Systems' FedSat mission, which is planned for 2001. This paper describes a 20/30 GHz transponder and its components, highlighting Australian monolithic microwave integrated circuit (MMIC), antenna and system engineering contributions.

A Ka-band down converter has been developed for use in a transponder to be flown on board a Low Earth Orbiting (LEO) satellite called Fedsat. The down converter employs a single Monolithic Microwave Integrated Circuit (MMIC) which combines the functions of a low noise amplifier and a mixer. The down converter unit has been designed with a particular emphasis on the choice of right materials, components, packaging and assembly techniques with a goal to achieve a low cost unit qualified for space environment. © 2000 IEEE.

A novel motion detector utilising a millimetre-wave array front-end, with signal processing that mimics insect vision, is described. The use of passive millimetre-wave detection enables a significant improvement over optical or infrared wavelengths, when a colliding object is obscured by rain, steam or other aerosols. This, for instance, used as a blindspot detector, will enhance driver safety in poor weather conditions. As insect vision techniques do not attempt to process an image, but rely on tracking moving edges, the processing tasks are less hardware intensive, resulting in a compact low-cost solution.

© 1998 IEEE. The finite-difference time-domain (FDTD) method is useful in many antenna applications because it facilitates modelling of complex structures and is capable of characterising antenna performance over a wide-frequency band. However, for antenna arrays of even modest size, the excessive computer storage and run-time may become prohibitive for design and optimisation purposes. Some work has been done with time-domain transform methods for computing weak coupling between antennas (Page et al. 1996). In this paper, an algorithm is developed using the Kirchhoff near-field to near-field transformation (Shlager and Smith, 1995) for the one-way coupling between antenna elements. This coupling representation is then applied to arrays in a manner analogous to an element-by-element analysis in the frequency domain, except that in the method described here the coupled currents at the antenna-feed ports are added in the time-domain so as to permit the introduction of true-time delays for wide-band beam steering. The advantages of the transform method over a full FDTD method are smaller computer storage and a reduction in late-time FDTD effects associated with reflections from the absorbing boundary on the outer surface of the computational domain and also from numerical dispersion and instabilities.

This paper will outline a method of accurately designing an active oscillator array of dipole-transistor elements based on satisfying the oscillation condition. The problem of frequency synchronization between the elements will be discussed and a novel technique for analysing the coupled oscillator behaviour of the active array will be presented.

This paper describes a new architecture for implementation of beam steering in a linear antenna array. A frequency translation process at the output of the antenna elements is used in conjunction with a series local oscillator feed to adjust the beam direction of the array by varying the local oscillator frequency. The architecture is compatible with hybrid microelectronic implementation on a planar circuit suitable for low-cost applications.

A method for designing an active array of dipole transistor (DT) elements is reiterated. It involves the determination of the element spacing in the array needed to force in-phase operation. The design equation, in conjunction with a method of moments analysis, can be used to determine the microstrip dipole dimensions and reactive feedback needed for oscillation at a particular frequency and power output level. A 2 element array is considered in a theoretical simulation and the results are explainable using intuitive reasoning.

The design of active dipole transistor (DT) elements is presented based on an equation describing the oscillation condition applied to the DT structure. A theoretical example of how to design a DT element for a specified frequency and power output is given, showing how feedback control can be used to satisfy the specifications. However, the question of how to provide DC power to the transistor without affecting the operation of the DT element still needs to be considered.

A novel motion detector utilising a millimetre-wave array front-end, with signal processing that mimics insect vision, is described. The use of passive millimetre-wave detection enables a significant improvement over optical or infrared wavelengths, when a colliding object is obscured by rain, steam or other aerosols. This, for instance, used as a blind-spot detector, will enhance driver safety in poor weather conditions. As insect vision techniques do not attempt to process an image, but rely on tracking moving edges, the processing tasks are less hardware-intensive, resulting in a compact low-cost solution.

The infinite-array microstrip dipole and microstrip folded dipole structures are modeled by a flexible method employing a spectral form of the periodic Green's function. The models are used to investigate the effects of feedline-induced and substrate-induced scan blindness and the relative significance of each effect for different substrate electrical thicknesses. Efficient implementation of the method allows well-converged results to be obtained quickly using desktop computers.

A design method for a coupled-patch oscillatory arrays is proposed and the operation of the oscillator is explained. The design is compatible with monolithic technology and is not restricted to a particular class of antenna element. Alternative antenna elements, more suited to millimeterwave applications could be used in practice.

A flexible method employing a generalized spectral form of the periodic Green's function, has been developed to model infinite-array microstrip structures of various configurations. The method is able to handle structures with dielectric substrates which may be finite in extent, or infinite in one or both dimensions. Efficient implementation of the method allows well-converged results to be obtained quite quickly using desktop computers.

This paper develops a flexible technique to analyze small size finite arrays by means of the finite array periodic Green's function, and attempts to improve the accuracy of the results by iteratively re-defining a better window function. Using a relatively simple structure, these methods demonstrate that the behavior of the active impedance of each element in a finite array can be approximated with limited success by the model. These methods may be useful for prototype modelling of more complicated microstrip structures in which the full analysis method would require prohibitively large computing resources.

An approach to the analysis of small finite arrays above a finite ground plane is presented. This approach has practical application in the development of small arrays for use in wireless local area networks or personal communication systems, where the need for compact housings precludes the use of extensive ground planes. For radiation in the forward half-space, the approach may also be useful for predicting the performance of arrays mounted on metal boxes.

Previous research had successfully analyzed the infinite array of substrate-supported metal strip antenna using the spectral form of the periodic Green's function. It has been shown that this technique can handle sub-sectionally defined basis functions in the Moment Method solution, as well as 3-dimensional geometry in the array elements. The computational efficiency achieved using the spectral approach coupled with known convergence acceleration technique, has also been demonstrated.

The effect of ground plane modification on the radiation of a dipole array is presented. Considered in this study are the cross-section dimensions of the waveguide backed aperture, spaced cells and a unit cell with a length and radius. Using the proposed method for analysis, the aperture fields may be determined from normal mode expansions in a similar way as for infinitesimal dipole fed horns. In this study, only the fields of the aperture are considered. Numerical results are discussed.

An active reflector constructed from orthogonal arrays of printed dipoles is analyzed in this paper. The configuration of dipoles is chosen to retain the maximum possible substrate area for amplifier and phase shifter components, with a view to eventual monolithic integrated circuit fabrication. It has been shown that for a reflector gain of 10 dB, oscillations may affect the array to performance.

Where large floor area packages must be used and damping with lossy material is not acceptable, the electromagnetic design of MMIC packages requires careful analysis for the minimisation of cavity resonance effects. If monolithic antenna elements are to be used then aspects of the antenna array design are directly relevant to package design and the suppression of resonances.

One implementation of a monolithically fabricated array has been proposed using linearly polarized metal strip antennas, where a resonant metal strip dipole is fabricated on an ungrounded extension of the substrate of a monolithic microwave integrated circuit (MMIC). In a typical implementation, such arrays are designed to transmit and receive either one or both linear polarizations, although circular polarization may be generated by selecting an appropriate excitation of perpendicular elements. For these phased arrays to be useful in the systems described, the level of cross-polarized radiation from the antenna elements must be small throughout the scan range. In this paper, mechanisms giving rise to cross-polarization by substrate supported metal strip antennas are investigated, and a method for reducing cross-polarized radiation is presented.

An experimental investigation of a simple antenna element suitable for integration on the substrate of a MMIC (monolithic microwave integrated circuit) is presented. These antennas are intended for use in egg-crate-type arrays. The structure occupies a small area of the substrate, is fed directly from a microstrip transmission line, and is therefore cheap to produce. This cost effectiveness is obtained at the expense of cross-polarization performance. In terms of gain, beamwidth, and bandwidth, this antenna appears to be quite attractive for use at millimeter wavelengths in large phased arrays.

An antenna consisting of a single wire connection from a source to a half-wavelength dipole above a ground plane is studied. With the inherent simplicity of the structure in mind, and the frequent need to connect a dipole antenna to an unbalanced output port (e.g., coaxial or microstrip line), the authors examine the performance of one such antenna and discuss the implications for similar geometry feeds with microstrip patch antennas. Current distribution and radiation patterns are presented. A number of observations on the operation of antennas fed by single wires or probes oriented perpendicular to ground are presented. Although the current distribution on the feed wire appears to be uniform, the description of this wire as a transmission line or nonradiating feed is not correct. The mechanism for the radiation from the feed wire is a traveling wave from the feedpoint to the junction with the dipole. Since the resulting radiating structure is asymmetrical, the radiation pattern is also asymmetrical.