Yiannis Vardaxoglou

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.

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.

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.

Simulations and Measurements of Dual-Band 2-D Periodic Leaky Wave Antenna

A dual band 2D leaky wave antenna is presented. The antenna is constructed from a double layer partially reflective surface suspended above a metallic ground plane, forming two Fabry Perot cavities corresponding to the two different resonant frequencies. The paper demonstrates the successful operation of the antenna through simulation and measurement.

Review of Highly-Directive Flat-Plate Antenna Technology with Metasurfaces and Metamaterials

A review of the development of enhanced directivity applied to high gain antennas is shown here, illustrating the various design possibilities. Fabry-Perot cavities (FPC) covered by partially reflective surfaces (PRS) made by high density dielectric layers or frequency selective surfaces is the standard way to obtain such antennas. Ground planes may be substituted by artificial magnetic surfaces to reduce the overall thickness, metamaterials with low permittivity have been used to generate highly directive beams as well. In all cases high directivity is produced by the excitation of low attenuating leaky waves in the antenna transverse direction

Microwave antennas and heterogeneous substrates using nanomaterial fabrication techniques

By exploiting the enhanced physical properties of nanomaterials and the advancement in nanotechnology, alternative methods of fabricating microwave antennas can be conceived. This paper will discuss the potential manufacturing advantages as well as different fabrication methods. By controlling the location of metallic and dielectric particles, integrated antennas and substrates can be made in one process. Electromagnetic advantages result from being able to add inclusions with different electrical properties into the host substrate and thereby create a new effective permittivity and permeability. This paper will review and analyse methods for calculating these effective properties.

3D-printed flat lens for microwave applications

This paper presents the design of a 3D-printed flat graded-index lens based on ray optics. The lens is comprised of several concentric dielectric rings with bespoke relative permittivities for transforming spherical waves into plane waves. 3D-printing was used to fabricate this lens with graded and tailored dielectric properties in a single process. The 3D-printed flat lens is low-cost and light-weight, but provides broadband and high gain performance. Measurement results show that the realised gain of the lens is 8 to 10 dB over the frequency band ranging from 12 to 18 GHz.

Design of Cylindrical Omni-Directional Patch Antenna with Superimposed EBG Surfaces

This paper presents the modelling and design of an omni-directional (azimuth plane) cylindrical patch antenna operating at 2.4 GHz and the directivity enhancement in the elevation plane by means of cylindrical Electromagnetic Bandgap (EBG) surfaces. The EBG surfaces are initially designed using planar modal analysis. They are used as Partially Reflecting Surfaces (PRS) and placed around the cylindrical patch at a resonant distance corresponding to the desired operating frequency. This distance is initially approximated using a simple analytical formula. Full-wave periodic analysis provides accurate results of the antenna operating frequency and performance. A finite 2.5 wavelength antenna has been simulated using a 3D full-wave software package and the results are presented.

Repeatability of embroidered patch antennas

The repeatability of the embroidery technology in fabricating wearable antenna is discussed in this paper. Two groups of rectangular microstrip antennas have been embroidered by conductive threads with different stitch spacings. Each group contains 8 identical antennas with 16 antennas in total. The repeatability of resonate frequency, bandwidth, gain, antenna efficiency, radiation pattern and cross-polarization are measured for different stitch spacings. The results demonstrate the potential of applying embroidery to antenna mass manufacture.