Our recent and ongoing research projects are:
· Orthopaedic Implant Monitoring Device
· High Speed Internet to Less Privileged
· Wireless Implantable Bio-Telemetry System and Miniature Antenna Design
· Wireless Freedom for Lab Rats
· Flexible and Wearable Antennas for Biomedical and Healthcare Applications
· Characterizing Properties of Carbon nano Tubes at Microwave Frequencies
· Electromagnetic Band Gap (EBG) Resonator Antennas
·
Leaky-Wave Antennas for Advanced Wireless Systems
· Shared Aperture Arrays for Space Borne Applications
· Novel Dielectric Resonator Antennas
· Focal Plane Arrays for Radio Astronomy
· Archimedian Spiral Metamaterials
· Frequency Selective Surfaces for Energy-Saving Glass Panels
· Dual-Band Artificial Magnetic Conductor (AMC) Surfaces
· Antenna Technologies for Ultrawideband (UWB) Systems
· High Gain Antennas with Planar Surface-Mounted Short Horns
· Photonic Crystal/EBG Based Horn Antennas
· Broadband Microstrip Patch Antennas for Wireless Computer Networks
· Theoretical Analysis of Photonic Crystal Structures
· New Closed-form Green's Functions for Microstrip Circuits and other Layered Structures
· Low-profile Dielectric-resonator (DR) Antennas
Implantable Electromagnetic Devices
Arthroplasty is the only solution to restore the mobility of a person whose joints are severely damaged by arthritis or injury. In this procedure, an orthopaedic surgeon removes damaged cartilage and bone from the joint, and positions new metal and plastic implants to restore the alignment and function of the knee. However, about 8-10% of these surgeries require the revision procedure due to various reasons like aseptic loosening, infection, dislocation, periprosthetic fracture and other mechanical complications. It is proposed that a non-contact micro motion sensor with the resolution of about 10 microns can help the healthcare professional to assess the health of the implant and therefore can potentially avoid the revision. This directly translates into a considerable freedom from pain and discomfort to the patient and financial burden to the healthcare system. However, currently, no modality exists that can cater to this application.
In this work, micromotion detection using eddy currents is explored for the first time in human body. Eddy current technology for distance sensing with industrial applications is quite mature with many commercial products in the market. However, since the sensor are positioned inside the bone in the near the orthopaedic implant, it is necessary to evaluate its response to the human body which is highly dispersive and inhomogeneous. For such an implantable sensor, there is space as well as power constraint.
In order to verify the idea, the eddy current sensor was fabricated on the Rogers 6010.2 substrate as used in simulations. To measure the impedance as a function of frequency Agilent PNA- N5242A was used. The sensor is connected to VNA by soldering SMA connector to the sensor directly. The VNA is initially calibrated using the E-cal module. This is followed by the port extension calibration to remove the effect of the SMA connector. The 2-port data for wires is measured separately by connecting them between two ports of the VNA. This data is used to remove the effect of wires by using 2 port fixture correction in VNA. To create micromotion, Newport's micromotion stage with its Conex-CC controller is used. The titanium implant is mounted on the stage backed by an ECCOSORB block to avoid the reflections. Care was taken to avoid placing the implant over the wires. The implant only covers the bone so that fields from sensor only interact with it. A cow bone is used for testing. It is cleaved from the tibial end. Three holes at 5mm, 10mm and 15mm are drilled using a power drill. The sensor is inserted in the holes and measurements are taken for 250 microns total motion in steps of 25 microns. A wet towel is kept to cover the bone to avoid desiccation. A MATLAB script is written to automate the motion of the plate and the capture data from VNA. To get the higher performance and noise reduction, point-based averaging technique is used. Additionally, the averaging for 50 samples is done with Matlab to smoothen the data. The entire setup is shown below.
International Patent Application
Orthopaedic Implant Monitoring Device
A small mm size sensor (10mm x 2mm) and a small data telemetry antenna (2.5mm x 2.5mm x 1.6 mm) when implanted inside the bone will determine the micro-motion of the orthopaedic implant giving an indication of the early implant failure. Developed @ WiMed Research Centre - Macquarie University.
We invented
a high-performance antenna beam-steering method that can provide high-speed
internet to regional Australia and Australian outback beyond what is possible
with NBN, and to billions of people across the globe who still do not have
proper internet connectivity, significantly enhancing their education, health and
thus quality of life through remote education and telemedicine.
Wireless Implantable Bio-Telemetry System and Miniature Antenna Design
The two major challenges associated with the conversion of a wireless system operating in air to an implantable version, antenna detuning and biocompatibility, are addressed in a coherent way. An RFID-based biomedical telemetry system designed for free-space operation was chosen as the starting reference. A new, pin-compatible, space-saving antenna with a ground plane was designed, fabricated and tested, to replace the original “free-space” antenna in the active RFID tag without making any other changes to the tag circuit, such that the tag would function well when it is placed under rat skin and fat. Biocompatibility and potential antenna detuning due to rat tissue variations were addressed in the design process, without significantly increasing the tag physical height, by applying a thin coating of biocompatible material directly over the antenna. The operation of the medical telemetry system was successfully demonstrated, with the tag placed under rat skin and fat, and its range of 60-72 cm was found to be sufficient to support medical research experiments conducted with rats in cages. Due to the biocompatible coating over the antenna, antenna matching is very insensitive to changes in tissue dielectric constants and thickness. The footprint of the new antenna is 33% less than that of the original antenna, its measured 10 dB return-loss bandwidth is 100 MHz or 11%, and overall efficiency is 0.82% at 920 MHz.
In this sequel, initially, when a module of our original system was placed under the skin of a rat, the wireless link failed completely. It could not send a temperature reading even a centimetre! The point of failure was the commercial antenna in the module that had been designed to work outside the body, in air. Such antennas do not work under rat skin because the electrical characteristics of skin (rat or human) are significantly different from that of air. Hence the main challenge was to design an antenna that works well when placed under the skin. In addition, it was necessary to cover the module and the antenna by biocompatible material, which also affects antenna performance. Possible variations of skin characteristics from one rat to another or one person to another were considered. Unlike the commercial antenna, we wanted our antenna to radiate less into the body of the rat/person and more away from the body because that not only increases the quality of the wireless link, maximum range (distance between implanted module and monitoring station) and battery life but also reduces the exposure of the body to radio-frequency waves. Indeed we had to consider the electromagnetic effects of fat and other material around the antenna. We were able to meet all these requirements with a novel compact antenna design that is approx. one third the size of the original commercial antenna. We successfully demonstrated wireless telemetry transmission of temperature with the new module placed under rat skin and the monitoring station placed at a distance of up to 80 cm! This range is sufficient for our immediate target application supporting new medical research by Professor Paul Pilowsky’s team. If necessary, it can be further extended by increasing the power level at the monitoring station.
Flexible and Wearable Antennas for Bio-Medical and
Healthcare Applications
A compact ultra wideband antenna is shown below with strong notch-band rejections up to VSWR = 26, that is tunable over a wide frequency range from 3.55GHz to 6.8GHz has been designed. To estimate the stub length to notch frequency for a given interfering application, analytical expressions for the normalized stub length which is independent of substrate dielectric constant is also presented. This helps to avoid hit-an-trail method and gives a good estimate of initial design parameters for notch. Proposed antenna has wide radiation patterns and yields a measured 10dB return-loss bandwidth from 3GHz to 10.5GHz.
Characterizing
Properties of Carbon Nano Tubes at Microwave Frequencies
Electromagnetic
Band Gap (EBG) Resonator Antennas (ERA)
Enhancing Radiation Characteristics of ERAs by Improving Aperture Phase Distribution
This work focuses on achieving superior radiation characteristics of ERAs by improving their aperture phase distributions. A unique method, utilizing full-wave simulations and analytical analysis, has been developed to design Phase Correcting Structures (PCS) for ERAs. This method uses actual phase distribution on the physical aperture of ERAs instead of relying on geometric optics. Several Phase Correcting Structures (PCSs) have been designed, which were later validated with the measurements of their fabricated prototypes. Tremendous improvement in the radiation performance is witnessed in both simulated and measured results. These exciting initial results validate our proposed methodology and indicate an existence of a great potential to be explored. The figure below shows the field propagation above an ERA: (a) without PCS, and (b) with PCS. It is clear that the field with the PCS is much more uniform and the energy is focussed towards broadside direction, thus, resulting in increased directivity.
Extremely Wideband High-Gain ERAs (Gain~15-20dBi, Bandwidths >50%)
Our most recent results on such wideband high gain antennas can be found in: “Achieving high gain-bandwidth through flat GRIN superstrates in Fabry-Perot cavity antennas,” Proc. 2014 IEEE International Symposium on Antennas and Propagation (AP-S/USNC-URSI), pp. 1748 – 1749, Memphis, Tennessee, USA, July 6-11, 2014.
Detailed antenna design along with experimental data of another of our wideband EBG resonator antenna having composite multi-layer superstrate, is published in the paper titled: "Wideband high-gain EBG resonator antenna with a small footprint and all-dielectric superstructures" in IEEE Transactions on Antennas and Propagation, vol. 62, no. 6, 2014.
Simple Dual-Band
ERAs
We have extended this concept for dual-band, dual-polarised and circularly-polarised antennas. We also designed a tri-band antenna following this concept. It needs only three low-cost unprinted dielectric slabs.
Low-Profile Wideband ERAs
We have designed and successfully tested wideband low-profile (thin) EBG resonator antennas. The breakthrough that contributed to this success is our design of a partially reflecting surface (PRS) with a positive reflection phase gradient. Thin single-dielectric-slab PRSs with printed patterns on both sides were investigated to minimise the PRS thickness and to simplify fabrication. Three such surfaces, each with printed dipoles on both sides, have been designed to obtain different positive reflection phase gradients and reflection magnitude levels in the operating frequency bands. These surfaces, and the EBG resonator antennas formed from them, were analysed theoretically and experimentally to highlight the design compromises involved and to reveal the relationships between the antenna peak gain, gain bandwidth, the reflection profile (i.e. positive phase gradient and magnitude) of the surface and the relative dimensions of dipoles. A small feed antenna, designed to operate in the cavity field environment, provides good impedance matching (|S11|< -10 dB) across the operating frequency bands of all three EBG resonator antennas. Experimental results confirmed the wideband performance of a simple, low-profile EBG resonator antenna. Its PRS thickness is only 1.6mm, effective bandwidth is 12.6%, measured peak gain is 16.2 dBi at 11.5 GHz and 3dB gain bandwidth is 15.7%. Please find details in a paper entitled “The Use of Simple Thin Partially Reflective Surfaces with Positive Reflection Phase Gradients to Design Wideband, Low-Profile EBG Resonator Antennas,” published in IEEE Transactions on Antennas and Propagation in 2012.Low-Profile
Dual-Band ERAs
Woodpile EBG
Material and Antennas
Then we designed a planar EBG resonator antenna. Shown below, it has a resonant cavity between a ground place and a 3D woodpile photonic crystal. We employed both microstrips and slots to feed the cavity, and investigated both linearly and circularly polarised antennas. The linearly polarised antenna design and experimental results are described in the paper entitled “A planar resonator antenna based on a woodpile EBG material,” published in IEEE Transactions on Antennas and Propagation,vol. 53, no. 1, pp. 216-223, January 2005.
Leaky-Wave Antennas for Advanced Wireless Systems
Antenna beam steering can bring significant benefits to advanced wireless systems. Microstrip leaky-wave antennas (MLWAs) are of particular practical interest because of their planar low-profile configuration, ease of fabrication, and beam-scanning capabilities. In this research several planar MLWAs and arrays are developed to radiate at boresight, in a conical beam around the boresight, with simultaneous dual-side-beam scanning, dual-band forward and backward beam-scanning, and continuous beam scanning from the backward to the forward direction. Moreover, methods and antenna designs are proposed to steer the beam at a fixed frequency, shifting beam-steering range, and fixed-frequency beam-steering in forward and backward directions.
Multi-band Dual-Polarized Shared Aperture Array
Multi-band dual-polarized shared-aperture (MBDP-SA) arrays are antenna arrays that operate in two (or more) frequency bands with dual-polarization in each band, and whose elements are integrated together into a common physical space by sharing the single aperture. The MBDP-SA array is of great interest in space-borne SAR system, because this technique can effectively reduce the payload and size of the antenna sub-system. In this research project, main efforts are focussed on three aspects: 1) improve the specifications of current Dual-Band Dual-Polarized Shared-Aperture (DBDP-SA) array; 2) construct Tri-Band Dual-Polarized Shared-Aperture (TBDP-SA) array; and 3) explore some new structures for DBDP-SA antenna.
Compact Dielectric Resonator Antennas with Ultra-Wide 60%-110% Bandwidths
We have recently made a significant achievement in the emerging ultra wide-band (UWB) wireless communication systems, which require antennas with bandwidths greater than 106%. In the past, the only way antenna engineers knew how to get such a bandwidth from a thin antenna was by removing the metal sheet underneath the antenna (known as “ground plane”). This is not an acceptable solution for practical systems because the lack of it allows the antenna to radiate both upwards and (unnecessarily) downwards (i.e. in to the electronic device on which the antenna is installed), wasting about half of its power. Saving power is crucial in UWB systems due to the severe power limits imposed by regulators. In 2011, we made a breakthrough in dielectric-resonator (DR) antenna research, by inventing a novel DR antenna with a full ground plane and a 110% bandwidth. This disproved the myth that such bandwidths cannot be achieved with full ground planes. This antenna, published in the prestigious IEEE Transactions on Antennas and Propagation in December 2011, is 29% smaller but has a 30% greater bandwidth than the next-best DR antenna, which does not even have a full ground plane. Hence it is ideal for next-generation ultra-fast medical and sensor applications.We theoretically and experimentally demonstrated that, by introducing a lower-permittivity full-length insert between the ground plane and a higher-permittivity dielectric resonator, dielectric resonator antennas (DRA) with ultra-wide bandwidths, in the range of 60%-110%, can be designed. Furthermore, the volume of such DRAs is reduced by approximately 50% using a finite planar conducting wall. Unlike vertical monopole-type hybrid UWB DRAs, these antennas radiate sufficiently in the upward direction. Unlike in printed monopole UWB antennas, the power radiated into the lower hemisphere is significantly less. An example prototype antenna, designed to operate in the FCC UWB band, has a dielectric volume of 12 x 8 x 15.2 mm3 (or 0.124 x 0.083 x 0.157 lambda3 at 3.1 GHz), and an average measured gain of 5 dBi from 3.1 to 10.6 GHz. These antennas exploit multiple low-Q modes with overlapping bandwidths to form an ultra-wide contiguous bandwidth. With the proposed dielectric arrangement, it is possible to efficiently couple a sufficient number of such overlapping modes to a 50 ohm feedline using a single, simple feed.
The antenna has a remarkably small footprint of 12x8 mm2 at 3.1 GHz - the lowest frequency of the FCC UWB band. Its dielectric volume is 1459 mm3, or 1.7x10-3 lambda3 at the lowest operating frequency of 3.1 GHz, and overall height is 15.2 mm or 0.157 lambda0. To place these results in perspective, it is worth comparing the new designs with the most wideband DR designs available in the literature. To the best of our knowledge, prior to this, the widest bandwidth ever obtained from a pure DRA design is 84% . The volume of the DR in that design is 0.225 x 0.172 x 0.062 lambda3 (= 2.4x10-3 lambda3) at its lowest operating frequency of 3.69 GHz. In that DRA, the DR is positioned in a non-traditional way, close to the edge of an orthogonal, “vertical” ground plane, which does not block radiation towards the lower hemisphere. The widest bandwidth demonstrated by a pure DRA with a traditional “horizontal” ground plane, (which can be employed to shield the rest from the antenna, as discussed previously) is 78%. The dielectric volume of that design is 0.31 x 0.09 x 0.21 lambda3 (= 5.8x10-3 lambda3) at its lowest operating frequency of 6.7 GHz.
We have demonstrated that extremely wide bandwidths (ratio-bandwidths up to 1:25) can be obtained from a specially designed printed antenna with a tapered semi-ring feed. One design is described in “A Printed Elliptical Monopole Antenna with Modified feeding Structure for Bandwidth Enhancement,” in IEEE Transactions on Antennas and Propagation, vol. 59, no. 2, pp. 667-670, Feb. 2011.
Focal Plane Arrays for Radio Astronomy
Dense focal plane arrays (FPAs) are a key technology for a new generation of Radio-telescopes. Their primary benefit is the rapid survey speed facilitated by the wide field-of-view provided by multiple beams. Recent advances have brought dense FPAs within reach of radio astronomy applications. A number of institutions have significant research programs in this field. This technology is being considered for the Square Kilometre Array (SKA) (www.skatelescope.org). The PhD project of Douglas Hayman, conducted with CSIRO ICT Centre and Division of Astronomy and Space Science, investigated beamforming aspects of FPAs and evaluated their performance in Radio Astronomy. A prototype interferometer-radiotelescope, built at CSIRO's Radiophysics Laboratory in Sydney, is used to demonstrate a suite of techniques forFPA beamforming and evaluation for this thesis. Beamforming solutions were experimentally demonstrated in our paper in IEEE Transactions on Antennas and Propagation, entitled “Experimental Demonstration of Beamforming Solutions for Focal Plane Arrays”.The THEA tile, shown below, is designed by ASTRON and used for the experimental component of this research.
Negative
Permeability of Spiral Metamaterials
Archimedean Spiral Metamaterials and Backward Waves
We have shown backward wave propagation and double negative parameters over a 19% bandwidth in a microstrip line loaded with series gap discontinuities and super-compact complementary Archimedean spiral resonator metamaterial particles. Moreover, our equivalent-circuit model for such unit cells almost perfectly described the structure for all practically important frequencies (by comparison with full-wave results). We also fabricated and tested compact filter circuits with only one or two complementary spiral metamaterial particles. Our results sre summarized in the paper entitled “Backward Wave Microstrip Lines with Complementary Spiral Resonators,” published in IEEE Transactions on Antennas and Propagation, Vol. 56, Issue: 10, pp. 3173-3178, Oct 2008.We derived design equations for Archimedean spiral resonators and tested them against full-wave simulations. The details are in the paper entitled “Design of monofilar and bifilar Archimedean spiral resonators for metamaterial applications,” published in IET Microwaves, Antennas & Propagation, vol. 3, no.6, p. 929-935, Sep.2009.
Frequency Selective Surfaces for Energy-Saving Glass Panel
Energy-saving
glass is becoming very popular in building design due to their
effective shielding of building interior against heat entering the
building with infrared (IR) waves. This is obtained by depositing a
thin layer of metallic-oxide on the glass surface using special
sputtering processes. This layer attenuates IR waves and hence keeps
buildings cooler in summer and warmer in winter. However, this
resistive coating also attenuates useful microwave/RF signals required
for mobile phone, GPS and personal communication systems etc. by as
much as 30 dB. To overcome this drawback, we designed and tested a
bandpass aperture type cross-dipole frequency selective surface (FSS),
etched in the coatings of energy-saving glass to improve the
transmission of useful signals while preserving IR attenuation as much
as possible. With this FSS, 15-18 dB peak transmission improvement can
be achieved, for waves incident with 45 degrees from normal for both TE
and TM polarizations.
Measurements and other results of this research, conducted in
collaboration with the Lund University in Sweden, are available in the
paper entitled “Cross-Dipole Bandpass Frequency Selective Surface for
Energy-Saving Glass Used in Buildings,” published in IEEE Transactions
on Antennas and Propagation, vol. 59, no. 2, pp. 520-525, Feb. 2011.
The effect of these FSSs on the transmission of infrared and visible
wavelengths through energy-saving glass was investigated theoretically
and experimentally in another paper in IET Microwaves, Antennas &
Propagation, Vol. 4, Iss. 7, pp. 955–961, 2010.
Switchable Frequency Selective Surfaces to Reconfigure Electromagnetic Architecture of Buildings
In large buildings and offices, frequency re-use methods will be required to enhance the spectral efficiency and capacity of wireless communication systems. This observation has led to the concept of electromagnetic architecture of buildings. Passive bandstop FSSs can be used to enhance the electromagnetic architecture of a building, and hence to improve spectral efficiency and system capacity, but switchable FSSs can provide a better reconfigurable solution. If switchable FSSs are placed in strategic locations of a building, they can be reconfigured remotely and rapidly, which is not possible with passive FSSs.
With collaborators in UK and Sweden, we designed and successfully tested a single-layer active Frequency Selective Surface (FSS) that is electronically switchable between reflective and transparent states. It can be used to provide a spatial filter solution to reconfigure the electromagnetic architecture of buildings. The FSS measurements show that the frequency response of the filter does not change significantly when the wave polarization changes or the angle of incidence changes up to ±45º from normal. The FSS is based on square loop aperture geometry, with each unit cell having four PIN diodes across the aperture at 90 degree intervals. Experiments demonstrated that almost 10 dB additional transmission loss can be introduced on average at the resonance frequency, for both polarizations, by switching PIN diodes to ON from OFF state.
For details, please refer to “Switchable Frequency Selective Surface for Reconfigurable Electromagnetic Architecture of Buildings,” in IEEE Transactions on Antennas and Propagation, Vol. 58, Issue 2, pp 581-584, February 2010.
Later we modified the FSS to obtain even better performance, for example, for both horizontal and vertical polarizations at oblique angles of incidence. The distance between the two layers has been successfully reduced to one eighth of free-space wavelength. This small distance makes it more compact as compared to the conventional Salisbury screen while still achieving an acceptable absorption in the stopband.
The details of our designs and test results can be found at “Oblique Incidence Performance of a Novel Frequency Selective Surface Absorber,” in IEEE Transactions on Antennas and Propagation, Vol. 55, no. 10, pp. 2931 – 2934, Oct. 2007, and “A Novel Absorb/Transmit FSS for Secure Indoor Wireless Networks with Reduced Multi-path Fading,” IEEE Microwave and Wireless Component Letters, Vol. 16 (6), pp. 378 - 380, June 2006.
AMC surfaces have many advantages and interesting properties due to their unique reflection characteristics, with near zero reflection phase. We have designed and prototyped a novel dual-band AMC surface, which has a very wide upper AMC band and a narrow lower AMC band, and therefore suitable for multi-band wireless/mobile applications.
Fully Printed
Quad-band Antennas for Wi-Fi IEEE802.11 and other WLAN Applications
How can I optimise
a UWB System to operate well over a range of directions?
Emerging ultra-wideband (UWB) communication devices will need to operate well, not just in one direction but over a range of directions. However previous UWB system optimisation techniques have been limited to one direction only. A system optimised in one direction may not work well in other directions due to pattern instability, or direction-dependent transfer function, of the antenna. We developed the concept of frequency-domain correlation patterns and proposed a figure of merit, the pattern stability factor (PSF), which can be determined from simulation of experimental results. With these new concepts, we have demonstrated the optimisation of UWB systems to operate well over a range of directions. The concepts and their applications are available in the PhD thesis and papers by Tharaka Dissanayake.
Antenna Techniques
and Technologies for Ultrawideband (UWB) Systems
In collaboration with University of Delhi, we have developed compact rectangular dielectric resonator antennas with surface mounted planar horns for gain enhancement. One configuration consists of an aperture-fed rectangular dielectric resonator antenna and a planar surface mounted horn. We have achieved 10 dBi gain and a good efficiency from this configuration. The surface mounted horn increases the gain of the standard dielectric resonator antenna by 4.9 dB. Total height of the prototype antenna shown in the figure is only 0.172 lambda and the aperture size is 0.96 lambda. These antennas can be easily adapted to low-profile, high-gain and array applications.
Waveguides and antennas made out of dielectric, as opposed to metal, are expected to perform better at Terahertz frequencies, as they do not suffer from the skin-effect loss of metal. We have investigated horn antennas, horn arrays, waveguides, bends and junctions made out of 3D woodpile photonic crystals, which can be implemented at THz frequencies in high-resistivity Silicon and other materials. Our concepts have been tested by fabricating and measuring scaled-up prototypes operating in microwave frequencies. We have also designed a special broadband coupler to couple a photonic crystal waveguide to a rectangular waveguide or a coaxial cable, for example for testing using a vector network analyser. We demonstrated > 6% bandwidth both theoretically and experimentally.
Broadband
Microstrip Patch Antennas for Wireless Computer Networks
We have designed and tested broadband, compact
E-shaped patch antennas for wireless communication networks, operating in
frequencies from 4.9 GHz to 6.0 GHz. We made two significant achievements.
First, we designed an E-shaped antenna, which is intrinsically compatible with
a printed microstrip circuit. It can be made out of a single sheet of metal and
can be mounted on a microstrip circuit without expensive coaxial connector.
Second, we designed a unique E-shaped antenna with corrugation to reduce the
width of antenna. We successfully miniaturised the antenna to fit it inside a
thin (4mm) PC (or PCMCIA) card extension. In fact, we were able to squeeze in
two of these antennas into a single PC card of standard width (54mm), for diversity
communications, and achieve excellent isolation (>20 dB) and matching
(<-10 dB) over the whole WLAN frequency band.
We have developed and successfully implemented, in both personal computers and supercomputers, efficient theoretical methods to analyse and design complex electromagnetic (microwave and optical) circuits based on photonic crystals (PC). Among our novel techniques is a PC-based Perfectly Matched Layer (PML) absorbing boundary for use with the finite difference time domain (FDTD) method in the analysis of waveguides in 3D photonic crystals.
We have applied these techniques to model wave
propagation in various guiding structures such as bends, junctions and tapers
in 2D and 3D crystals. From this analysis, we can obtain the transmission and
reflection coefficients, propagation characteristics, phase and delay response,
etc., of a component or a system.
New Closed-form
Green's Functions for Microstrip Circuits and other Layered Structures
Integrated-design
of Hybrid-resonator Antennas for Broadband Wireless and other Communication
Systems
Singularity-enhanced
Finite-different Time-domain (FDTD) Method for Diagonal Metal Edges, Strips and
Films
We developed the world's first and still the only singularity-enhanced FDTD method for metal edges not parallel to the grid. The edges were assumed to be diagonal to cell faces. Compared with the conventional spit-cell model, the computer memory required for an FDTD analysis of a structure could be reduced by up to 27 times and the computing time could be reduced by up to 81 times, without sacrificing the accuracy of results. On the other hand, when the same grid was used, the accuracy of results improved by a factor of more than 3 compared to the split-cell model, and a factor of more than 7 compared to the staircase model. The new equations were stable in all tests, and even in most demanding tests when the computational speed was further maximised by increasing the time step (Dt) to the maximum allowed by the FDTD method! (i.e. stability factor of 1! )
The key to this success was the derivation of enhanced FDTD equations for nodes near the edges by considering rigorously the singular nature of the electromagnetic fields. The table here shows the improvement of accuracy achieved by using the enhanced FDTD equations. The new equations are simple to implement in a standard FDTD code. They are ideal for the analysis and design of microstrip components and high-speed digital circuits where thin metal films or strips with diagonal edges are encountered.
We designed and tested the world's first low-profile, circularly polarised, rectangular dielectric-resonator antenna (DRA) in 1995. The radiating element of this antenna is shown in the photograph. We have also designed many other dielectric-resonator antennas, including a low-profile linearly polarised DRA, for various applications (see publications). We pioneered the FDTD analysis of DR antennas and published the first radiation patterns of a DR antenna obtained using the FDTD method in 1995.
Australian Antenna Measurement Facility (AusAMF)
The facility currently consists of a spherical near-field turn-key NSI-700S-50 system within a 6m x 3.3m x 3.3m anechoic chamber. It has been designed to operate up to frequencies of 20 GHz, and uses an Agilent PNA (E8362B) as a receiver. The measurement system is capable of supporting a ~40kg antenna under test (AUT) up to a diameter of approximately 1.2m. Details of the standard gain horns and the probes available at AusAMF are as follows:
|
Waveguide
Band |
Frequency (GHz) |
Probe |
Standard
Gain Horn |
|
WR975 |
0.75
- 1.12 |
x |
x |
|
WR650 |
1.12
– 1.70 |
x |
x |
|
WR430 |
1.70
– 2.60 |
x |
x |
|
WR340 |
2.20
- 3.30 |
x |
x |
|
WR229 |
3.30
– 4.90 |
x |
x |
|
WR159 |
4.90
– 7.05 |
x |
x |
|
WR112 |
7.05
– 10.00 |
x |
x |
|
WR90 |
8.20
– 12.40 |
x |
|
|
WR75 |
10.00
- 15.00 |
x |
x |
|
WR51 |
15.00
- 22.00 |
x |
x |