Cj Railton

An adaptive microstrip patch antenna for use in portable transceivers

This paper describes an adaptive frequency tunable microstrip patch antenna. The introduction of an adaptive feedback loop enables the patch antenna to optimise the antenna-feed impedance match. As a result, the performance of the antenna is less affected by external disturbances such as coupling to nearby objects. Measurements evaluating the performance of the proposed antenna, in terms of transmitted power and bit error rate, are presented.

Derivation and application of a passive equivalent circuit for the finite difference time domain algorithm

The widely used finite difference time domain (FDTD) algorithm in its standard form is conditionally stable, the condition being the well-known Courant criterion. Much research has focussed on modifying the standard algorithm to improve its characterisation of geometrical detail and curved surfaces; these modified algorithms, however, may easily be conditionally stable-there is no value of time step that stabilizes the algorithm. The authors present a passive electrical circuit that, by virtue of its formal equivalence with FDTD, provides a criterion by which unconditionally unstable algorithms may be avoided. As an example the passive circuit criterion is used to remove the instability from a contour-path FDTD algorithm.

Calculation of losses in 2-D photonic Crystal membrane waveguides using the 3-D FDTD method

The three-dimensional finite-difference time-domain method is used to obtain loss per unit length in a two-dimensional photonic crystal membrane waveguide by simulating three different length guides. Results are shown for propagation both above and below the light line. The results are compared with a Fourier expansion method and good agreement is obtained above and below the light line.

Optimized absorbing boundary conditions for the analysis of planar circuits using the finite difference time domain method

It is shown that the description of absorbing boundary condition algorithms (ABCs) in terms of single incident plane waves does not provide sufficient information for choosing the best ABC for planar waveguide termination. A technique for optimizing the ABCs that results in a return loss from a wideband pulse less than -50 dB is demonstrated. This technique reduces the risk of loss of accuracy due to mode conversion at the boundary. The use of these optimized ABCs considerably improves analysis results for an important category of microstrip components. For boundaries transverse to the direction of propagation, it is shown that inaccuracy and late time instability can result if the boundary is placed in regions of high field strength. >

Fast Finite Difference Time Domain Method for the Analysis of Planar Microstrip Circuits

Although the FD-TD method has been successfully applied to the analysis of planar microstrip circuits eg (1), It is necessary to make improvements so that the time of analysis can be reduced. One such improvement consists in using an irregular grid (2). The aim of this paper is to show that, although the majority of published applications of FD-TD make use of a uniform grid and some authors have rejected non-uniform grids as being inaccurate (3), they are on the contrary well suited to the analysis of complex structures such as filters, and that, together with open boundary conditions and broadband excitation, they contribute considerably in reducing the computing time.

A comparison of the properties of radiating boundary conditions in the FDTD method for finite discretisation and non-planar waves

The availability of effective radiating boundary conditions (RBCs) for use with the finite difference time domain (FDTD) method is essential for the efficient application of the technique to scattering and radiation problems. The majority of published analyses of the behaviour of various RBCs are restricted to the case of plane wave incidence and infinitely fine discretisation, situations which never occur in practice. In the present contribution, the behaviour of RBCs in realistic situations is presented and it is shown that the plane wave behaviour is not a good guide as to the behaviour in practical cases. The best RBC for use in general cases is discussed. >

Analysis of a UWB Hemispherical Antenna Array in FDTD With a Time Domain Huygens Method

Electromagnetic modeling is needed in a wide variety of large and complex situations. Existing numerical techniques such as finite difference time domain (FDTD) can, in principle, solve any problem no matter how large or complicated given a sufficiently powerful computer. However, in practice, there remain problems which require more computer power than is available. Recently, the time-domain Huygens (TDH) approach has been shown to be effective for enabling large problems such as propagation on body area networks (BANs) to be modeled in FDTD. In this paper, it is shown that the much larger problem of the conformal antenna array, which is used in the MARIA breast cancer tumor detection system, is also very amenable to this technique with even greater savings in computer resources. Accurate results are obtained using less that a tenth of the resources needed to solve the same problem using existing advanced FDTD tools. The details of how this method is applied, and the choices which need to be made, are discussed.

Calculation of the dispersive characteristics of open dielectric structures by the finite-difference time-domain method

Abs~uct- An enhanced three-dimensional Finite-Difference Time-Domain (FDTD) technique is applied to the characterization of the fundamental and higher order modes of single and coupled image guide structures. The basic FDTD algorithm is modified to include multidimensional changes of permittivity and an irregular mesh is used for computational efficiency. In this paper FDTD calculations are compared with experimental and theoretical results found in the literature and good agreement is found.

Design and simulation of a photonic crystal waveguide filter using the FDTD method

The FDTD method is used to design a InP photonic crystal (PC) waveguide filter operating at 1534 nm. The filter uses strong mode coupling effects which result in a small device area of 8 /spl mu/m /spl times/ 10 /spl mu/m.

Analysis of Coupled Tilted Slot Antennas in FDTD Using a Novel Time Domain Huygens Method With Application to Body Area Networks

Despite the undoubted versatility and effectiveness of the finite-difference time-domain (FDTD) method and its enhancements, there remain some problems which require more computer power than is practical. An example of such a problem is the coupling between two or more tilted antennas in the presence of a scattering environment such as is encountered in a body area network (BAN). The dual challenge of a wide range of scales and complicated structures which are not aligned with a Cartesian mesh are addressed using a novel Time Domain Huygens (TDH) approach. Results and comparisons with measurements are presented showing the effectiveness of the method. In addition, the measured and predicted variations of BAN propagation characteristics with body size are investigated.