A low-profile rectangular dielectric-resonator antenna

A rectangular dielectric-resonator antenna (DRA) with a very low profile (length-to-height ratio ≈6) is presented. This aperture-coupled antenna is almost perfectly matched to the 50 Ω input and radiates like a magnetic dipole at 11.6 GHz. It is also well matched at 13.0 GHz, but the pattern is more directional due to the influence of a higher order mode. Theoretical antenna patterns, obtained using the FDTD method, compare well with measured patterns in the E and H planes     

Pulse-receiving characteristics of resistively loaded dipoleantennas

The pulse-receiving characteristics of resistively loaded dipoles are analyzed using a time-domain numerical technique. The Wu-King nonreflecting dipole and several other dipoles with higher and lower distributed resistances are considered. The time-domain responses of these dipoles to Gaussian electromagnetic pulses (incident in boresite direction) are calculated. Frequency-domain receiving transfer functions are obtained using the fast Fourier transform (FFT) technique. Dipoles terminated with high resistance loads are also considered. The effect of the distributed resistance and terminal resistance on the pulse response and bandwidth is discussed     

Linear array of woodpile EBG sectoral horn antennas

A technique is described for creating linear array antennas that conform to the natural stacking sequence of the woodpile electromagnetic bandgap (EBG) material. Each element in the linear array consists of a woodpile EBG sectoral horn antenna. The electromagnetic confinement mechanism within each horn antenna relies wholly on the 3-D EBG of the woodpile material. The array element has a typical sectoral horn pattern with a directional beam in one principal plane and a broader beam in the other. The bandwidth of the sectoral horn is almost equal to that of the defect EBG waveguide. Measured and theoretical results for radiation patterns, impedance bandwidth and gain of a sectoral horn antenna made from alumina are described, and theoretical results for a design made from silicon are presented. It is shown that the layer-by-layer nature of the woodpile EBG material enables sectoral horn antennas to be easily stacked together in the E-plane to create linear arrays. Analysis of the mutual coupling as a function of element separation and its effect on reflection coefficient are presented for a two-element linear array in silicon. Theoretical analyses for fixed and scanned beam linear arrays of silicon woodpile EBG sectoral horns are described and finite-difference time-domain results are compared with array theory. The fixed beam arrays are designed for high directivity while the scanned beam array enables wide angle beam steering through the use of parasitic array elements.     

New closed-form Green's functions for microstrip structures theory and results

This paper presents an efficient technique to evaluate the Green's functions of single-layer and multilayer structures. Using the generalized pencil of function method, a Green's function in the spectral domain is accurately approximated by a short series of exponentials, which represent images in spatial domain. New compact closed-form spatial-domain Green's functions are found from these images using several semi-infinite integrals of Bessel functions. With the numerical integration of the Sommerfeld integrals avoided, this method has the advantages of speed and simplicity over numerical techniques, and it leads to closed-form expressions for the method-of-moments matrix coefficients. Numerical examples are given and compared with those from numerical integration     

Capacitive sensors for in-vivo measurements of the dielectricproperties of biological materials

Two open-ended coaxial sensors for in vivo measurements of the dielectric properties of biological tissues at low radio frequencies are described. The high fringing-field capacitance of these sensors allows accurate measurements of high-water-content tissues at frequencies as low as 10 kHz. Each sensor is represented by two capacitances, which are calculated using the method of moments. Theoretical and experimental results for experimental sensors terminating a standard 14-mm coaxial line with a GR900 connector are presented     

Cylindrical tissue model for magnetic field stimulation of neurons:effects of coil geometry

An analytical solution for the electric field induced in a homogeneous cylindrical conductor under quasi-static conditions from current in a coil is used to model peripheral nerve stimulation with magnetic fields. A variety of coil geometries is analyzed in terms of the spatial derivative of the induced electric field along a long straight nerve, parallel to the axis, in a human-arm model. The results of these computations are found to be in general agreement with conclusions regarding the optimization of stimulating coils derived from analyses of the semi-infinite tissue model. The differences and their physical basis are pointed out     

GA/FDTD technique for the design and optimisation of periodic metamaterials

An efficient and powerful full-wave electromagnetic technique is presented to characterise and design periodic metamaterial structures. First, the spectral finite-difference time-domain (FDTD) method with periodic boundary conditions and uniaxial perfect matched layer is employed to predict the performance of a mushroom-like artificial magnetic conductor (AMC) surface and further extended to characterise a negative-refractive-index material consisting of lumped and distributed transmission-line elements. Then, a new computational technique is developed to design and optimise periodic metamaterial structures by integrating the spectral FDTD method with a genetic algorithm (GA), namely the micro-genetic algorithm. This computational technique is successfully applied to design and optimise single-band and dual-band AMC structures consisting of a frequency-selective surface and a ground plane. It is demonstrated that the GA/FDTD technique is a very effective approach for the design and optimisation of periodic metamaterial structures consisting of dielectrics and conductors of arbitrary configurations     

Waveform optimisation of UWB radio systems over range of directions

The waveform of the source pulse applied at the input of an UWB antenna can be optimised to obtain maximum peak radiated field in one direction. Presented is a systematic technique that helps the UWB system designer to achieve the best peak radiated field in a range of directions. Since the transfer functions of all known printed UWB antennas are direction dependent, application of such a technique is crucial in the system design when an UWB system is required to radiate close to the peak over a range of directions.     

E-shaped patch antennas for high-speed wireless networks

Thin, broad-band, E-shaped microstrip patch antennas (ESPAs), operating in the 5-6 GHz frequency range, are presented. They are intended for high-speed (IEEE 802.11a, 54 Mb/s) wireless computer local area networks (WLAN) and other wireless communication systems. They are suitable for WLAN adaptor cards in the PCMCIA (also known as PC) format, allowing users of current notebook computers to upgrade to this high-speed wireless standard at a low cost. Importantly, our antennas are thin enough to be accommodated in a PCMCIA card of standard 5-mm thickness, without making the antenna end thicker than the card itself. Two different closely spaced antenna pairs are also presented for diversity. A new ESPA configuration with a microstrip feed is presented for easy integration with microwave transceivers. In all cases, within the two IEEE 802.11a WLAN bands (5.15-5.35 GHz and 5.725-5.825 GHz), the reflection coefficient at the antenna input is <-10 dB and in both antenna pairs, mutual coupling between the two antennas is <-20 dB.     

Compact diversity antenna for wireless devices

A compact diversity antenna, consisting of two E-shaped microstrip patch antennas, is presented. It has a wide bandwidth, covering all frequency bands of 5-6 GHz WLAN systems operating under IEEE 802.11a and HiperLAN2 standards. Corrugations have been introduced to reduce the overall width of the diversity configuration to 54 mm - the width of a standard PCMCIA card. The isolation between the two inputs is greater than 20 dB and the signal correlation is less than 0.2 over all WLAN bands.