William G. Whittow

CPW-Fed Cavity-Backed Slot Radiator Loaded With an AMC Reflector

A low profile coplanar waveguide (CPW) fed printed slot antenna is presented with uni-directional radiation properties. The slot antenna radiates above a closely spaced artificial magnetic conducting (AMC) reflector consisting of an array of rectangular patches, a substrate and an electric ground plane. The electromagnetic bandgap (EBG) performance of the cavity structure between the upper conducting surface in which the slot is etched, and the ground plane at the bottom of the reflector, is investigated using an equivalent waveguide feed in the place of a half-wavelength section of the slot antenna. From the reflection coefficient of the equivalent waveguide feed one can determine the frequency band where minimum energy will be lost due to unwanted radiation from the cavity sides. The dimensions of the cavity were found to be very important for minimum energy loss. Experimental results for the final antenna design (with a size of 1.02λ0×0.82λ0×0.063λ0), mounted on a 1.5λ0×1.5λ0 back plate, exhibit a 5% impedance bandwidth, maximum gain in excess of 10 dBi, low cross-polarization, and a front-to-back ratio of approximately 25 dB. This low-profile antenna with relatively high gain could be a good candidate for a 2.4 GHz WLAN application.

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.

Experimental Verification of a Modified Specific Anthropomorphic Mannequin (SAM) Head used for SAR Measurements

This paper investigates a method of facilitating specific absorption rate (SAR) measurements in the head when using a 1800 MHz radiation source placed in front of the face. A specific anthropomorphic mannequin (SAM) head phantom is modified by removing the rear most part to enable fully-automated scanning of the face region by a DASY4 electric-field probe. Prior to the modification, simulations were carried out in FDTD to establish the optimum area to be removed. This paper compares predicted local SAR values behind the face with actual measurements carried out using the new modified SAM phantom head. Measurements show good agreement with simulations, indicating that the modified SAM head is suitable for SAR measurements when the source is placed in front of the face.

Effective Permittivity of Heterogeneous Substrates With Cubes in a 3-D Lattice

This letter studies the behavior of heterogeneous dielectric substrates created by including micro-sized cubes of different electromagnetic (EM) properties to an otherwise homogenous host medium. The letter looks at the effect of the volume fraction of cubic inclusions (dielectric or metallic) to the effective EM properties of the heterogeneous medium. It is well known that the effective permittivity of the mixture is dependent on the properties of the host and inclusions as well as the size and spacing of the cubes. EM simulations using a plane-wave excitation have been used to carry out these studies. An inversion process using a rectification algorithm was employed to correctly obtain the effective permittivity from the scattering parameters of the mixture. The analytical results of the infinite medium using canonical equations and a volume equivalence showed good agreement with the EM simulations and measurement of our samples of finite thickness. This letter shows that cubic inclusions can produce a higher effective permittivity than was previously found with spheres.

On the effects of straight metallic jewellery on the specific absorption rates resulting from face-illuminating radio communication devices at popular cellular frequencies.

This paper presents simulated and measured phantom results for the possible effects that head worn jewellery may have on the relative levels of energy absorbed in the human head with cellular enabled mobile communication devices. The FDTD electromagnetic code used with simple and complex anatomical mathematical phantoms was used to consider the interactions of metallic jewellery, heads and representative sources at 900 and 1800 MHz. Illuminated metallic pins of different lengths were positioned in front of the face. Initially, a homogenous phantom was used to understand the relative enhancement mechanisms. This geometry allowed the results to be validated with the industry standard DASY4 robot SAR measurement system related to the CENELEC head. Jewellery pins were then added to an anatomically realistic head. The relative increase in the 1 g and 10 g SAR, due to a pin with a length 0.4lambda near the eyebrows of a complex, anatomically realistic head was approximately three times at 1800 MHz. Such pins increased the SAR averaged over a 1 g or 10 g mass by redistributing the energy absorbed inside the head and focusing this energy towards the area of the head nearest to the centre of the pin. Although, the pins increased the SAR, the SAR standards were not breached and the jewellery produced lower values than those of previous studies when the source was positioned close to the ear.

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.

Feasibility Study of 4G Cellular Antennas for Eyewear Communicating Devices

A feasibility study of 4G cellular antennas operating in the LTE, GSM, DCS, PCS, and WLAN2400 standards for wirelessly connected eyewear is presented. The target bands are 700-960 MHz and 1.7-2.7 GHz. The antenna designs are capacitive coupling element types, with simple layout printed on one side of the printed circuit board (PCB) substrate. Three different antennas are examined in terms of obtainable bandwidth potential, reflection coefficient, and specific absorption rate (SAR) values considering two human-head models (SAM and Visible Human). The best antenna is -6 dB matched and has radiation efficiencies around 14% and 36% in respectively low and high frequency bands. Based on simulation data, SAR values could be above the 1-g standards.

Novel planar AMC for low profile antenna applications

In recent years, the realization of Artificial Magnetic Conductors (AMCs), also designed as high impedance surfaces (HISs) or Perfect Magnetic Conductors (PMCs), has been an active area of research as they can replace perfect electric conductors (PECs) for low profile antennas and other microwave applications. In this paper a planar AMC using circular split ring resonators (SRRs) printed on grounded dielectric substrate is proposed. The simulation results verify that the magnetic conductor is successfully accomplished over narrow bandwidth = 0.25 GHz. As an antenna application, the return loss of a horizontally positioned dipole antenna placed above the proposed AMC and the conventional PEC ground planes are investigated. The results confirm that the split ring resonators can successfully be used to replace the antenna conventional ground plane in order to improve the strength of the radiating fields and to reduce the global thickness of the low profile antennas. The performances of the proposed AMC are studied using finite element method ANSOFT-High Frequency Structure Simulator (HFSSTM v.10) and numerical simulation model is developed to predict the reflection phase profile of such structures.

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.