R.D. Seager

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.

Characterising the linearity of an optically controlled photoconductive microwave switch

The linearity response of a photoconductive switch on microstrip line is presented at 2GHz. A silicon switch is exposed to incident signal power of up to 1W and controlled via illumination with a range of optical intensities at a wavelength of 980nm in order to characterise the linearity in terms of harmonic content. Reported single tone output third order intercept (TOI) was measured as 63dBm under 200mW of optical incident light. The study presents photoconductive switches as a promising alternative to conventional microwave switches in high power applications.

Frequency selective wall for enhancing wireless signal in indoor environments

With the increasing use of mobile computing devices such as PDAs, laptops, and the expansion of Wireless Local Area Networks (WLAN), there is growing interest in increasing productivity and efficiency through enhancing received signal power. This research demonstrated a band pass square-loop Frequency Selective Surface (FSS) in walls to increase the efficiency of certain communication systems. The FSS is simulated by Empire XCcel. Remcom ‘Wireless InSite’ is used to simulate indoor propagation and to predict the performance. Significant improvements are shown using an FSS based surface.

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.

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].

Close coupled resonant aperture inserts for waveguide filtering applications

A two-layer frequency selective surface (FSS) is used as a very compact and lightweight transverse waveguide filter element. A narrow-hand transmission response is produced from two layers, which, otherwise, in isolation would exhibit a broadband response. Measured results are compared with theoretical data obtained from a Transmission Line Matrix (TLM) based modeling method. Reduction in the passband bandwidth of a factor of four has been achieved using the proposed structure.

Indoor band pass frequency selective wall paper Equivalent Circuit & ways to enhance wireless signal

An objective of the work has been to create a band pass square mesh-patch array Frequency Selective Surface (FSS) wall paper. Modifying the indoor wireless physical propagation environment to increase the coverage of certain communication systems was investigated and demonstrated in this research. General analysis approach for rectangular waveguide with square section is presented. The FSS is analysed by Computer Simulation Technology (CST) Microwave Studio (MWS) and Equivalent Circuit (EC) modelling. Remcom ‘Wireless InSite’ is used to simulate indoor propagation and to predict the performance. The concept has been tested inside ‘Wireless InSite’ and compared with VisiWave site survey data. Significant improvements are shown using an FSS based surface.

Investigating the effects of control lines on a frequency reconfigurable patch antenna

The objective of the paper is to investigate the effects of metallic control lines on a frequency reconfigurable patch antenna. The designed antenna resonates at 3 different frequencies in range of 3–4GHz. Simulation and measurement results of return loss with and without control lines are presented. We have also discussed the challenges of implementing the bias lines.

Modified Designs for UWB Planar Monopole Antennas

This paper reports a theoretical study of a planar monopole antenna for use in the 3.1 GHz-10.6 GHz UWB band for later integration into consumer electronic products. Therefore the emphasis of the research is related to minimizing the size of the monopole while maintaining the matching in the desired frequency range. Simulations, using the Empire Software Suite, show that the impedance matched bandwidth (RL>10 dB) can be significantly increased by bevelling the bottom edge of the monopole and also the impedance match at the lower end of the band can be improved by judicious placement of a shorting pin. The use of a 1 mm wide shorting pin yields a structure that resembles a PIFA antenna. It is possible to treat the monopole antenna as a modified PIFA and apply transmission line theory to predicting the resonant frequencies and the return loss. A combination of shorting pin with bevel shows significant promise in the size reduction of the UWB antennas. The key point is the careful position of the shorting pin (with the bevel) on the monopole that to give a very good match through out the UWB band. This paper reports an investigation of the effect of the antenna dimensions (height, bevel angle and position of shorting pin) on its broad band response. The results of this study show that it is possible to reduce the size of the antenna elements significantly below lambdamax/4, when additional shorting pins are used on the antenna. The distributed shorting pins can be understood to work as a matching network for the antenna.