Alford Chauraya

Frequency and beam reconfigurable antenna using photoconducting switches

A design for an optically reconfigurable printed dipole antenna is presented. A wideband coplanar waveguide (CPW) to coplanar stripline (CPS) transition is used to feed the balanced printed dipole. Two silicon photo switches are placed on small gaps in both dipole arms equidistant from the centre feed. Light from two infrared laser diodes channelled through fiber optic cables is applied to the switches. With the gaps in the dipole bridged, the antenna resonates at a lower frequency. Measured return loss results that compare well to the simulated values are also presented, showing a frequency shift of nearly 40%. The change in bore-sight gain along with radiation patterns are also presented. Activating each switch individually results in a near 50/spl deg/ shift in beam nulls.

Inkjet-Printed Microstrip Patch Antennas Realized on Textile for Wearable Applications

This letter introduces a new technique of inkjet printing antennas on textiles. A screen-printed interface layer was used to reduce the surface roughness of the polyester/cotton material that facilitated the printing of a continuous conducting surface. Conducting ink was used to create three inkjet-printed microstrip patch antennas. An efficiency of 53% was achieved for a fully flexible antenna with two layers of ink. Measurements of the antennas bent around a polystyrene cylinder indicated that a second layer of ink improved the robustness to bending.

A Compact and Low-Profile Tunable Loop Antenna Integrated With Inductors

We present a frequency-tunable, compact loop antenna which consists of a transmission line on a ground plane, two shorting posts, and two inductors which are serially connected between the posts and the edge of the transmission line. By properly choosing the inductance of the inductors, the operating frequency of the antenna can be controlled without seriously sacrificing fractional bandwidth. To demonstrate the operating mechanism, the equivalent circuit of this antenna is included. The characteristics of the antenna with various inductors integrated are also investigated. Fabricated antennas show that the operating frequency can be shifted from 2.07 GHz to 1.2 GHz using off-the-shelf inductors. Using two 33-nH inductors achieves an antenna with an electrical size as small as 0.118lambda times 0.013lambda times 0.047lambda. The validity of this antenna is demonstrated by experimental results.

Embroidered wearable antennas using conductive threads with different stitch spacings

This paper is focused on using conductive threads to design flexible antennas with textile features which means antennas can be embroidered directly into normal clothes. The fabric microstrip antennas are made from commercial conductive threads. The gain and efficiency of fabric antennas have been measured and compared with a reference copper patch antenna. Effects from different stitches geometries within the fabric antenna are discussed. The results demonstrate the feasibility of wearable antennas.

Embroidered Wire Dipole Antennas Using Novel Copper Yarns

This letter presents a method of fabricating wearable antennas by embroidering novel fine copper yarn. In this work, fine copper wires are first twisted together to create a physically strong and yet flexible thread. A digital embroidery machine was used to create dipole antennas. The dc resistance of the antenna arms along with the return loss, radiation patterns, and efficiency of the antennas have been measured. The results are compared to embroidered dipoles using commercially available conductive threads and etched copper antennas.

High performance flexible fabric electronics for megahertz frequency communications

This paper investigates the concept of using conductive threads for fabricating electronics including antennas at microwave frequencies. A number of commercial conductive threads have been considered. Digital embroidery has been used to create samples with different stitch types. This paper will provide a wide range of practical advice about fabricating samples using such materials. The threads have been examined by assessing their DC resistances at rest and while under physical strain and also the RF performance of transmission lines. The results show there is a wide range in performance between different conductive threads.

A flexible fabric metasurface for on body communication applications

This paper presents a flexible Frequency Selective Surfaces (FSS)/High Impedance Surface (HIS) structure for wearable communication systems. When designed using flexible electro-textiles for radiating elements and fabric dielectric substrates periodic electromagnetic structures may offer performance advantages in wearable antenna design. The traditional printed circuit etching technique has been used on electro-textiles to design HIS structure showing electromagnetic bandgap (EBG) behaviour. The existence of an EBG is experimentally verified from 10 to 12GHz by a transmission line technique. The design frequency can be used for satellite communication applications.

Towards a compact low frequency woven antenna

The fabric based antenna presented in this paper shows a good bandwidth around the operating frequency for a COSPAS/SARSAT satellite beacon. The degree of size reduction is excellent and further reduction appears to be possible. While a complete evaluation of the effects of curvature and protective layers on the pattern and the Axial Ratio remain to be completed the effect of flexing the antenna, or mounting it in protective material, does not move the resonant frequency significantly and the antenna appears to possess an admirable degree of immunity from flexing. This technology shows considerable potential for the production of satellite communication systems as well as, because of is compact nature, integration within planar furlable arrays for a wide range of markets. Further reduction in the groundplane size will be sought by using metamaterial techniques [1].

Frequency switchable microstrip filter for microwave frequencies

This paper presents a frequency agile parallel-coupled microstrip filter. The centre frequency of the device may be switched very rapidly between two discrete values by applying optical illumination to a pair of silicon dice, which are mounted on the printed side of the board. Measurement results indicate that one may achieve a shift of 359MHz in the centre frequency by illuminating both dice with only 30mW of optical power. The optical power was measured at the end of the light delivery system. Increasing the level of optical power to 200mW reduces the passband insertion loss (measured at the centre frequency) from 3.614dB to 2.037dB. The minimum return loss values when both dice are illuminated with 30mW and 200mW are 10.10dB and 14.82dB respectively. The percentage bandwidth in the off-state differs from that in the on-state by only 1.86%. The maximum frequency switching range is approximately 380MHz. The measured and simulated results for the filter are in good agreement.

Embroidered Frequency Selective Surfaces on textiles for wearable applications

An assessment of a Frequency Selective Surface (FSS) for wearable applications is presented. The textile FSS array was created on 0.8 mm thick felt material using a fast and cost effective embroidery technique with conducting threads. This operates at 2 GHz with transmission coefficient lower than 10 dB. The FSS structure was also modelled using commercial simulation tools. This work is towards low-loss textile FSS structures for wearable applications.