The Australian research in the field of microwave technology is not very large. However we have some small but reasonably advanced capability and achievements. In this paper some of the Australian developments are discussed namely: GaAs Monolithic Microwave Integrated Circuits, MM-wave Local Area Networks, Antennas for Communications and Radioastronomy and application of Photonics to Warfare.

We have developed a planar devic technology consisting of 0.15-µm Au/WSiN-gate GaAs-heterostructure MESFETs (HMESFETs) fabricated by self-aligned ion-implantation. The gate-drain breakdown voltage has been improved to 10 V by using an asymmetric LDD structure, and the maximum oscillation frequency is 190 GHz. Because asymmetric and symmetric FETs can be fabricated simultaneously, this technology is suitable for use in making multi-functional millimeter-wave MMICs.

This paper proposes a novel architecture and MMICs for an integrated 2-32 GHz front-end of a spectrum analyzer. The architecture achieves miniaturization by eliminating the large YIG tracking filter and also achieves multi-octave measurement with less than one octave sweep of the first local oscillator. The MMIC's demonstrate ultra-wideband performances with reduced chip sizes by utilizing newly developed FET cells for power combination, multi-order frequency conversion, low leakage variable resistance, and active impedance translation. The MMIC's are a fundamental/harmonic frequency converter, a variable attenuator, a single-pole triple-throw switch, a single-pole double-throw switch, a distributed pre-amplifier, and an active LC lowpass filter. All the MMIC's are smaller than 1 mm², except the pre-amplifier and the filter.

A new three-dimensional MMIC structure and an ultra-wideband miniature MMIC balun are proposed. The MMIC is a combined structure of multilayer MMICs and U-shaped micro-wires. This technology effectively reduces chip size and enhances MMIC performance. The proposed balun is constructed with three narrow conductors located side by side. The U-shaped micro-wire technology is employed to reduce the insertion loss and chip size. 1.51 dB insertion loss over 10 to 30 GHz, and 2 dB and 5 degrees of amplitude and phase balances over 5 to 35 GHz have been obtained. The intrinsic area of the balun is only 450800 µm, about 1/5 to 1/3 the area of recently reported miniaturized MMIC baluns.

A subharmonic injection-locked oscillator (ILO) MMIC chain is proposed for the local oscillators and synthesizers used at millimeter-wave frequencies. A fabricated, primary 11-GHz-band injection-locked oscillator MMIC for the first stage ILO in the ILO-chain MMIC, achieves a wide subharmonic-injection-locking range at the subharmonic factors, 1/n (n=1, 2, 3, ), of 1/1, 1/2 and 1/3. The ILO MMIC abilities for synthesizer applications were confirmed with an injection-locking time of only 100-200 nsec, which is less than 1/100 that of PLL oscillators, and also with free-running oscillation performance and a wide injection locking range within a temperature range of -30 and 80.

A new GaAs monolithic switch IC that can be operated with a single positive control voltage is developed. The implemented IC is provided two different biasing configurations with the switching FETs. Each FET can be biased independently by large capacitors fabricated employing the BST (Barium Strontium Titanate) technology. The fabricated SPDT (Single-Pole-Double-Throw) swicth IC shows insertion loss less than 1.0 dB and isolation over 25 dB in the frequency range of 0.1 GHz to 1.9 GHz with a single control voltage of 3 V.

A novel nonlinear analysis method of high power amplifier instability has been developed. This analysis method deals with a loop oscillation in a closed loop circuit and presents the conditions for oscillation under large-signal operation by taking account of mixing effect of FETs. Applying this analysis to the high power amplifier instability that an output power for the fundamental wave (f₀-wave) decreases at some compression point where a half of the fundamental wave (f₀/2-wave) is observed, it has been found that this instability is caused by an f₀/2 loop oscillation. In addition, it has been verified by analysis and experiment that the oscillation can be removed by employing an isolation resistor in a closed loop circuit.

A low contact resistivity of 4.410^-7 Ωcm² for AlGaAs/GaAs HBTs was realized using Pt/Ti/Pt/Au base metal and a 810¹⁹ cm^-3 highly-doped base. A high f_max of 170 GHz was achieved by reducing a base resistance. The formation of oxide-free interface between an AlGaAs graded base and Pt-based metal was demonstrated with Auger electron spectroscopy. The optimization of the growth condition conquered the rapid current-induced degradation in the highly Be-doped HBTs. An extremely wide bandwidth of 40 GHz was attained by a Darlington feeback amplifier fabricated using these high-f_max HBTs. These properties indicate that the application of AlGaAs/GaAs HBTs can be expected to extend to future ultrahigh-speed optical transmission systems.

We propose an axially symmetrical Fabry-Perot multiple-device oscillator operating at an axially symmetrical TEM_01n-mode, which has an excellent feature of uniform device-field coupling required for high efficiency power combining. By carrying out the boundary element analysis, it is shown that a plane-mirror output structure is remarkably advantageous compared with a concave-mirror output structure to obtain an adequate output coupling and to enable stable operation characteristic with respect to the axial mode number n. Experiments in X-band confirmed this excellent performance and achieved almost perfect power combining of efficiency as high as 106% and 99% for six- and eight-device case, respectively.

Design techniques are presented for high performance microstrip bandpass filters using GaAs FETs for loss compensation. The filters are based on conventional planar filter topologies with the addition of GaAs FET negative resistance circuits to amplify the signal within the resonators via a reflection-mode of amplification. Three practical filters have been demonstrated using these negative resistance techniques: (1) A filter employing an active loop configuration, (2) a dual-mode microstrip ring resonator filter, and (3) an end-coupled half-wavelength resonator filter. The investigation of this negative resistance method of loss compensation has led to the development of an exciting new type of miniaturised filter which employs MIC microstrip resonators with MMIC negative resistance chips bonded into the filter for loss compensation. This approach has the advantage of combining the proven capabilities of established MIC microstrip filter topologies with the excellent reproducibility of the MMIC loss compensation circuits.

In this paper, a novel noise parameters extraction technique for microwave packaged BJT and FET is proposed. The noise parameters of packaged BJT and FET for the entire operating frequency band can be obtained from the four noise parameters measured at a single frequency or a few frequencies. The predicated results obtained with this method agree well with the measured data. As a result, the novel noise parameters extraction technique can be used to predict the noise with a minimum effort.

A new mm-wave IC, constructed by flip-chip bonded heterojunction transistors and microstrip lines formed on Si substrate, has been proposed and demonstrated by using MBB (micro bump boding) technology. Millimeter-wave characteristics of the MBB region has been estimated by electro-magnetic field analysis. Good agreements between calculated and measured characteristics of this new IC (named MFIC: millimeter-wave flip-chip IC) have been obtained up to 60 GHz band. Several MFIC amplifiers with their designed performances have been successfully fabricated.

A 1.5 GHz band Si power MOS amplifier module with 50% total efficiency, 1 W output power and 30 dB power gain has been developed for front-end transmitter of digital cellular telephones. A combination of a highly efficient power MOSFET for the output stage and an integrated two stage MOS amplifier for the driver with an impedance matching circuit minimizing the length of striplines made it possible to achieve high total efficiency, high power gain, and smaller size of the amplifier module.

In this paper, a waveguide-fed slot-coupled microstrip antenna is proposed as enhanced feeding structure of microstrip antenna and an analysis is pesented. The presence of dielectric substrate between a strip and a slot is explicitly taken into account in this analysis. The evaluation of the antenna characteristics is carried out using the method of moments and the spectral domain approach in terms of the electric current distribution on the strip and the magnetic current distribution on the slot.

A novel thick ground plane is proposed as a support for a slot-coupled microstrip antenna and as a heat sink for an MMIC installed on the back plane of the active array antenna. A multi-layer structure of ground planes is also studied for the benefit of easy installation of MMICs. The influence of this thick metal ground plane with a mono- and multi-layer has been investigated in detail. Both measured and calculated results of VSWR and calculated results of the back lobe are shown in detail. The calculated results of VSWR agree well with the measurements. It is made clear that the thickness of the ground plane can be extended to twenty times that of the antenna substrate while maintaining the antenna's performance. An LNA composing an MMIC was developed, attached to the back of the antenna, and operated at 23 GHz. The measured results of this active element agree well with calculated ones and confirm the applicability of the novel design.

In this paper, mutual coupling S₂₁ between RMSA (ring-shaped microstrip antenna) elements was estimated by the EMF method based on the cavity model. Then, the validity of the proposed method was tested by experiments. The experiments confirmed satisfactory agreement between the computed and experimental data for S₂₁ in both E- and H-plane arrangements. In addition, a circularly polarized planar array composed of R-MSA elements was designed on the basis of the data of S₂₁. The experimental results of such a planar array demonstrated high performance in radiation pattern as well as axial ratio property. Furthermore, the active reflection coefficient Γ in the R-MSA array was also investigated in both equilateral and square arrangements. The computed results of active reflection coefficient in the array demonstrated high performance in both arrangements.

Thin-film slot antennas for 700 GHz submillimeter wave radiation were designed on the basis of the experimental results obtained at microwave frequency regions, and fabricated with photolithographic methods. The antenna patterns measured for the HCOOH laser radiation agreed well with the theoretical antenna pattern. This shows that the fabricated antenna works as a slot antenna in the 700 GHz submillimeter region.

The high-T_c superconducting active antenna proposed here for millimeter and submillimeter radiowave communications, uses a YBCO slot antenna with a series Josephson junction array to increase the normal-state resistance of the junctions, in order to ensure impedance matching between the antenna and the junctions. The antenna is a coplanar waveguide fed slot antenna, which can be easily and monolithically combined with the Josephson junctions. The design frequency of the antenna is 10 GHz and the obtained bandwidth of a VSWR less than 2 was 4.1%. Normal-state resistance values of the junction array could be confirmed by measuring I-V characteristics and 100-MHz impedance measurements, and both agree very well. Microwave mixing experiments were carried out using the junction array with the antenna, and the experiments showed that the conversion gain of the junction was proportional to the number of the junctions. The conversion gain of an eight-junction mixer with the antenna was found to be -6 dB.

This paper presents an analytical study and computer-based model of radio wave polarization propagating through a microcell. It covers the following topics: the influence of random orientation of a handset terminal on the performance of communication systems using either a linearly or circularly polarized base-station antenna; an analysis of the computer-based simulation of the power response on different polarizations in a street-canyon microcell.

The fundamental TE₁₀ mode in a rectangular waveguide of a square cross section is degenerate with TE₀₁ mode. A quarter wavelength resonator made of a dielectric square waveguide is, therefore, applied for a small-sized bandpass filter, just like dual mode filters for base stations in the mobile communication. In this paper, the methods to couple the two modes are first studied, including cutting a corner of the resonator and adding some metal electrodes on its end face. Both methods help to flow the rf current of the odd mode at the corner, resulting in decrease of the series inductance and thus increase of the resonant frequency. The coupling constant, that is proportional to the difference of the odd and even-mode's resonant frequency, can be controlled by the perturbations mentioned above. The coupling to the external circuit is adjusted by an electrode fabricated also on the end face. It is connected to a microstrip line and capacitively couples to the resonant modes. The coupling strength increases with the dimension of the electrode. The adjustment of the resonant frequency is carried out by the similar electrode on the end face and connected to the center of the side of the square cross section. The frequency decreases with the length of the electrode. The unloaded Q is measured to be of around 500 for 5510 mm resonator of ε_r=93. The optimum aspect ratio for the resonator is found in terms of the Q value. The simplest bandpass filter, i.e., a two-stage bandpass filter is designed and fabricated using 5510 mm resonator. It is mounted in a square hole made in a printed circuit board and excited by a microstrip line. The frequency characteristics are in good agreement with the expected values.

A signal-to-noise enhancer with a bandwidth that is six times as wide as that of the conventional type is presented. A new circuit construction, the combination of two MSSW filters which have the same insertion loss in the broadband and two 90 hybrids, is effective to remarkably extend the bandwidth. The enhancement of the enhancer amounts to 20 dB in the operating frequency range of 1.9 GHz150 MHz in 0 to 60 degrees centigrade. This enhancer has accomplished FM threshold extension because the S/N is improved by 1 to 7 dB below the C/N of 9 dB. It was demonstrated that this new enhancer is effective for noise reduction in practical DBS reception.

A rat-race hybrid-ring which includes a coupled-line called microwave C-section is proposed for size reduction. The perfect input match, isolation, equal power split and certain phase differences between two output ports can be satisfied at center frequency as in a normal hybrid-ring. The size of the proposed circuit becomes smaller than that of a normal rat-race built up with a folded non-coupled 3/4-wavelength transmission line, although the frequency characteristics are slightly damaged by the electromagnetic coupling between two folded strips. Theoretical results based on the even and odd mode decomposition method are in good agreement with those of the experimental circuit fabricated at 1 GHz.

Interdigital transducers (IDTs) with leaky-SAWs propagating on 36 YX-LiTaO₃, and 41 and 64 YX-LiNbO₃ were theoretically analyzed, providing a new equivalent circuit. This equivalent circuit included attenuation constant due to leakage as well as conductance caused by bulkwave radiation. All circuit parameters were derived by solving integral equations. Fundamental experiments showed fairly good agreement between theoretical and experimental results, which gave very accurate design tools for leaky-SAW devices.

This paper describes newly developed miniaturized stepped impedance resonators with a double coaxial structure (DC-SIR's) and their application to bandpass filters. The new DC-SIR's using dielectric material are devised for more compact and lower frequency bandpass filters. Fundamental characteristics such as resonance properties and unloaded-Q make it clear that DC-SIR's have attractive features that miniaturization can be achieved without Q-factor degradation. Trial 400 MHz bandpass filters incorporating DC-SIR's are also made. Experimental results of bandpass filters proved that DC-SIR's are applicable to lower frequency band radio equipment and able to contribute to the expansion of applicable frequency ranges of dielectric coaxial resonators.

In this paper we will propose a deterministic approach to model the radio propagation channels complex indoor environments. This technique applies the SBR method to find equivalent sources (images) in each launched ray tube, and sums the receiving amplitude contributed by all images coherently. We verify our SBR/image approach by comparing the numerical results in two canonical examples where closed-form solutions exist. The good agreement indicates that our method can provide a good approximation of high frequency radio propagation inside corridors where reflection is dominant. In the special case of a curved corridor, which can not be solved by analytic methods, we find a "focusing" effect that at some certain point the receiver will receive high power, even though it is out of sight. This SBR/image method can be enhanced by including the wall penetration and wedge diffraction effects, and even more complicated indoor environments will be tackles in the near future.

The simulation of a specific absorption rate (SAR) with a temperature distribution becomes more important in the treatment planning for microwave hyperthermia. The simulation technique can also be used to estimate SAR distribution inside human body under hazardous electromagnetic (EM) field circumstances. In the simulation, to use exact permittivity of biological tissues becomes very important to obtain accurate SAR distribution. The permittivity of the medium is very sensitive to the temperature. Therefore, it is considered that the SAR distribution is also very sensitive to the tissue temperature. In this paper, SAR distribution is calculated using FDTD method considering tissue temperature under the electromagnetic (EM) field irradiation. Simulations of temperature distribution are also performed using heat transfer equation. In addition, temperature depending blood flow is taking into account to obtain temperature depending SAR distribution. The results can be used to estimate temperature depending heat generation which can be applied such as microwave hyperthermia treatment.

Multifrequency microwave radiometry has been investigated for non-invasive measurement of temperatures in a human body. In this paper, we propose a new temperature profile model function, which is based on thermo-physiological considerations, for use in model fitting method of retrieving a temperature profile from a set of multifrequency radiometric data. The microwave radiometric technique using the new model function was tested by numerical simulations against animal experiment and clinical data reported elsewhere. The results show that the microwave radiometric technique can be used effectively to measure temperature profiles in tissues over a depth range from 0 to about 4.5 cm.

An optoelectronic technique to control both the amplitude and phase of a radio frequency (RF) signal is presented that uses two electrically controllable birefringence mode nematic liquid-crystal spatial light modulators (ECB mode nematic LC-SLMs). An experimental circuit was built and its performance was examined. The intensity could be changed down to -25 dB, and a phase shift of up to 240 degrees was achieved, by changing LC-SLM supplied voltages. Carrier-to-noise ratio (CNR) and intermodulation characteristics of an RF signal were measured. It was, for the first time, found that CNR was not degraded by the amplitude control and phase shift performed by the LC-SLMs.

This paper proposes a new type of optically controlled BFN (beam forming network), an electro-optic BFN using an optical waveguide structure. In this BFN, antenna beam forming is performed using conventional optical variable phase shifters and conventional optical variable directional couplers. An electro-optic BFN can easily utilize monolithic integration capability that will be advantageous to microwave stabilization. In order to discuss practical applicability, microwave characteristics and beam forming characteristics were examined using an experimental BFN fabricated on a LiNbO₃ substrate. Resulting from electro-optic lightwave control, linear phase shifting and variable amplitude distribution were measured at various microwave frequencies. Without any other control except for optical offset frequency locking and applying constant voltages, typical short term fluctuation in L-band microwave was measured to be within 3 degrees_p-p in phase and 2.5 dB_p-p in amplitude, respectively. For the first time, an electro-optic BFN was successful in performing beam forming in an L-band array antenna as well as coaxial cables. It was also verified that radiation pattern measured in 60 degree beam steering using the experimental BFN was comparable to that calculated using conventional microwave BFNs. The experimental results show the feasibility of utilizing an electro-optic BFN in future advanced microwave/millimeter-wave array antenna systems.

In this paper, we presented an analysis of single and coupled microstrip lines covered with protective dielectric film which is usually used in the microwave integrated circuits. The method employed in the characterization is called partial-boundary element method (p-BEM). The p-BEM provides an efficient means to the analysis of the structures with multilayered media or covered with protective dielectric film. The numerical results show that by changing the thickness of the protective dielectric films such as SiO₂, Si and Polyimide covered on these lines on a GaAs substrate, the coupled microstrip lines vary within 10% on the characteristic impedance and within 25% on the effective dielectric constant for the odd mode of coupled microstrip line, respectively, in comparison with the structures without the protective dielectric film. In contrast, the single microstrip lines vary within 4% on the characteristic impedance and within 8% on the effective dielectric constant, respectively. The protective dielectric film affects the odd mode of the coupled lines more strongly than the even mode and the characteristics of the single microstrip lines.

This work is concerned with a dynamic analysis of complex uniplanar guide-wave structures for MMICs at millimeter-wave frequencies. The enhanced spectral domain approach is effectively used to model such uniplanar structures with trapezoidal conducting strips involving microshielding enclosures. A wide range of line propagation and impedance characteristics is obtained for slotline and coplanar waveguide (CPW). The effect of different conductor profiles on line characteristics is discussed in detail. Results show an excellent agreement with other works. A class of dispersion-related curves are presented for design consideration.

The dielectric resonator technique is commonly used for microwave surface resistance measurements of High Temperature superconducting (HTS) films. Thickness of super-conductors and its impact on measurement results has not been taken into consideration so far. A theoretical mode-matched solution analysis of a TE₀₁₁ 10 GHz sapphire resonator was performed. The results of this analysis demonstrate that the thickness of the films under test can significantly affect the resonant frequencies (f_res) and quality factor Q of the resonant system, particularly when the thickness is less than three times the penetration depth (λ) of the films at the operating temperature. In such cases the microwave properties of the substrate affect f_res and Q. For HTS films' thickness relatively small as compared to λ, measured quality factors and resonant frequency may also be affected by substrate thickness and the conductivity of the backing plates of the system. The presence of air gaps between the sapphire and the HTS films does not significantly influence surface resistance measurements. However they can markedly affect the surface reactance from which the penetration depth is calculated.

Closed-form solutions of the characteristic initial value problem for electric and magnetic fields propagating as nonsinusoidal plane TEM-waves in lossy unbounded media are calculated with Riemann's method and discussed in detail. As an application, the reflection and transmission of waves on a planar boundary is examined, when one semi-infinite medium is lossy.

The scattering characteristics of a waveguide T-junction with an inductive post are analyzed by the port reflection coefficient method (PRCM), combined with the mode-matching technique. Variation behaviors of the scattering parameters are provided as a function of the operating frequency and the dimensions of the junction. The results are helpful for the design of power dividers using this type of T-junction configuration.

A full confocal Gaussian beam open resonator system that determines the dielectric properties of low-loss materials in the 60-GHz band is developed. To achieve high Q values a quasi-optical coupling method is used to feed the resonator. It is connected to a computer-controlled HP 8510C vector network analyzer for automatic measurement. The frequency variation method is used and the data are processed using the open resonator scalar theory. Results from 96% and 99.5% alumina samples with thicknesses ranging from 0.38 mm to 1 mm, are presented in the V band, with loss tangent values of the order of 100 µ radians. This system should be able to measure substrates as thin as less than 0.1 mm to 0.3 mm, which are the thicknesses of substrates in practical use.

The radiation behavior of a parallel-plate-fed slit in a thick conducting screen is examined. The Fourier transform and the mode-matching technique are used to obtain simultaneous equations for the transmitted field inside the thick conducting screen. The simultaneous equations are solved to represent the transmitted and scattered fiels in simple series forms. The numerical computation is performed to illustrate the behavior of the radiation from the parallel-plate-fed slit. A substantial reduction in the reflection coefficient is possible by choosing a thickness of the conducting screen.

A Ku-band transversal filter with a center frequency of 12 GHz and a bandwidth of 6 GHz using directional couplers made of a multilayer ceramic has been proposed and developed. The directional coupler can realize a wide range of frequency characteristics, e.g. coupling of 3.50.5 dB in the frequency range of 10 to 17 GHz and a wide range of coupling values, i.e. 3 to 35 dB. Calculations have confirmed that the increase in insertion loss due to a decreasing Q-factor can be much less than that for a resonator filter. The transversal filter was fabricated without additional tuning, and measured results agreed well with calculated values.

An experimental study on propagation characteristics in a room of a modern office building using a 57.5 GHz carrier is described. The objective of the study is to provide initial information about the path-loss and fading characteristics for millimeter-wave wireless indoor communication systems. The area of the floor of the room is about 90 m² and the room was almost empty with no furniture except the experimental apparatus. A wide-beam scalar feed horn transmission antenna and an omnidirectional receiving antenna were used and set to be with the same height. The measured area was divided into many "squares" to characterize the propagation. The variation of square transmission loss was calculated, and the regions where the maximum square transmission loss was observed were pointed out. It became clear that the distance power law for square transmission loss was approximately of the order d^-2 along the direct path. Rician distributions for fast fading were derived in almost all squares of this room. The spectra for the fast fading envelope were also derived. From the propagation point of view, the results show that no extreme difficulty seems to exist in developing wireless communication systems in the 60 GHz band.

A field matching technique is used to analyse an N-port structure which includes a radial cavity and H-plane coupled rectangular waveguides. Based on this analysis, a PC based algorithm for calculating the scattering parameters of this structure is developed. This algorithm is tested against a more involved Finite Element package (HFSS) and measurements. An excellent agreement between the two software packages and measurements is obtained.