Electromagnetic Band Gap (EBG) Resonator Antennas

We have designed, fabricated, and measured antennas based on 3D EBG structures (i.e. photonic crystals). These flat microwave antennas give a gain of about 20dB and a very good efficiency. The antenna shown left has a resonant cavity between a ground place and a 3D woodpile photonic crystal. It is fed by a microstrip patch.

Broadband Microstrip Patch Antennas for Wireless Computer Networks

We have designed broadband E-shaped patch antennas and stacked patch antennas suitable for the next generation, high-speed, UNII band (IEEE 802.11a) and other wireless communication networks, operating in frequencies from 4.9 GHz to 6.0 GHz. Both linearly polarised and circularly polarised antennas are available.

To the left is a linearly-polarised antenna that we designed to fit into a thin (4mm) PC (or PCMCIA) card extension. In fact, two of these antennas can be included in the PC card extension. The theoretical and measured return loss figures of one antenna are shown in the graph on right.

Theoretical Analysis of Photonic Crystal Structures

The wave propagation (light bending without loss!) through a 90 bend in a 3D crystal

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 refection coefficients, propagation characteristics, phase and delay response, etc., of a component or a system.

3D Photonic Crystal Experiments

New Closed-form Green's Functions for Microstrip Circuits and other Layered Structures

When combined with the spatial-domain Method of Moments (MoM), our new closed-form functions now enable efficient and accurate analysis of microstrip circuits and antennas with minimum approximations. The key feature in this new MoM is that the four-dimensional integrations in MoM matrix elements can be solved analytically, completely eliminating the need for expensive numerical integrations. Our new closed-form functions are simpler and more flexible than previous such functions, and (unlike previous ones) they do not require additional (Taylor series or other) approximations.

The computer time required for the analysis of an example microstrip line using the new MoM was three times less than the next best method, which required some numerical integrations. The figure demonstrates the excellent accuracy of the new closed-form Green's functions. It compares results from the new method and from numerical integration, for a spatial-domain Green's function of a microstrip structure at two frequencies.

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.

Low-profile Dielectric-resonator (DR) Antennas

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.