Antenna frequency and beam reconfliguring using photoconducting switches

This paper presents the use of photoconducting switches in antennas for reconfiguring operating frequencies and radiation patterns. It has also been demonstrated that these switches can be used in optically controlled phase shifters. A frequency shift of 40% is achieved with a dipole antenna and an array of patch antennas show beam scanning covering 30deg

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 shift in beam nulls

Measurement techniques for polar electromagnetic bandgap structures using an air spaced microstrip line

The ability to accurately pinpoint with a high degree of accuracy the occurrence of the stop-band property in the newly engineered EBG materials is fundamental to their establishment. Measurement methods capable of achieving this have been proposed in literature but require intricate adjustments to suit particular requirements. In this paper we report on a repeatable measurement technique for characterising the bandgap properties of EBG structures using an air spaced microstrip line. The device constructed is simple, economical, robust and capable of quantifying the properties of a wide range of EBG materials. A tapered microstrip line transition is used to match a 50 coaxial port. Simulation and measurement results using a Polar-EBG are presented to show the versatility of the proposed technique. In addition to this we demonstrate that by changing the orientation of the surface under test (SUT), transverse electric surface wave measurements can be carried out. This apparatus and measurement technique is particularly applicable to fabric based EBG materials where measurements are especially challenging

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

Flexible radio frequency connectors for textile electronics

A new approach to interfacing fabric based wireless systems to traditional electronics circuitry is presented. Measurements show possible insertion losses of the connector to be < 1 dB up to frequencies of about 4 GHz when electroplating has been used to increase the hook and loop conductivities. This reported work points towards an interconnection system that is flexible and will allow the removal and replacement of conventional electronics connected to textile based systems

Non-uniform mesh for embroidered microstrip antennas

This paper presents a non-uniform meshed embroidered structure for wearable microstrip patch antennas. The non -uniform meshed patch antenna (NMPA) has significantly less conductor coverage than a conventional patch antenna without significantly compromise the antenna performance. For wearable applications, less conductor coverage reduces the usage of the specialised conductive materials which are currently expensive. The embroidered NMPA reduced manufacturing cost and improves the flexibility. In this paper, the surface current distribution and the effect of the meshing size of NMPAs have been simulated and analysed. Fully textile embroidered NMPA on felt substrate has been fabricated and measured. Representative results showed the NMPA had a 60% total antenna efficiency with 20% conductor area coverage

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

Compact and low-profile frequency agile loop antenna integrated with inductors

We present a frequency agile loop antenna which consists of a suspended transmission line and two inductors. Using appropriate inductors, the operating frequency of the antenna can be controlled without seriously sacrificing its performance. We derived an equivalent circuit of this proposed compact and low-profile antenna. Results from some prototypes showed that a frequency tuning range as high as 870 MHz can be achieved using off-the shelf inductors. In the case of integrating two inductors of 33 nH, an electrical size of the antenna as small as 0.118 λ × 0.013 λ × 0.047 λ is achieved

Fabric based frequency selective surfaces using weaving and screen printing

Two examples of fabric based frequency selective surfaces (FSSs) are presented. The FSSs are produced by using screen printing and weaving. Both measured and simulated data are presented showing excellent agreement and performance for the FSSs when compared with the simulated data. The performance of these samples points towards a useful screening technique using fabric hangings and wall coverings in a range of applications where temporary electromagnetic wave ingress or egress needs to be controlled

Simulation methodology to model the behavior of wearable antennas composed of embroidered conductive threads

Simulation methodology to model the behavior of wearable antennas composed of embroidered conductive thread