Stephen Boyes

Measurement and Performance of Textile Antenna Efficiency on a Human Body in a Reverberation Chamber

With the advent of on-body communication research in recent years, there is a growing need for antenna developments that satisfy a wide criteria (one being minimal efficiency degradation) in order to be integrated successfully onto human subjects; one promising development is the textile antenna. In this paper we investigate the efficiency performance of some newly designed small sized textile antennas on live human subjects using a reverberation chamber. First, we show that the material selection of these textile antennas can have a crucial effect on the on-body frequency detuning and efficiency levels, as via a comparison we determine that a lossier textile antenna in free space can actually outperform a higher free space efficient textile antenna when placed on-body. This has a profound impact on the material design choices for these small sized antennas. Second, we investigate the performance effects under bent conditions and finally we show that the overall performance of the textile antenna can be mitigated somewhat by variations in on-body distances from the human subject. It is revealed that in some cases a small 20 mm distance from the body is sufficient for the radiation efficiency to approach the free space levels. Theoretical, simulated and experimental evidence is presented to verify the conclusions.

On-Body Characterization of Dual-Band All-Textile PIFA

Antenna performance in terms of re∞ection coe-cient, bandwidth, radiation pattern and e-ciency is expected to be severely in∞uenced during on-body deployment. Besides addressing the need for a systematic on-body evaluation procedure, this work presents an in-depth discussion on the measured degradation relative to free space operation. Considering a practical deployment scenario, the two antenna designs are flrst optimized in proximity of a human- emulating box using a commercial simulator. ShieldIt textile is chosen to build the antennas conductive components, and this prototype is then benchmarked against another similarly-dimensioned prototype constructed using copper foil. For each material, two dual-band prototypes are fabricated, one resonating at 2.45GHz and 5.2GHz, and the other at 2.45GHz and 5.8GHz. Two realistic on-body deployment locations are chosen to be investigated, on the chest and back, considering two antenna orientations | one radiating away from the user, and the other radiating along the body. Free space and on-body re∞ection coe-cient, bandwidth and radiation pattern are evaluated for each prototype in an anechoic chamber, while a reverberation chamber is utilized to determine their e-ciency. All measurements were carried out using the same human volunteer. Evaluations show that coupling distance and conductivity are the main factors in determining e-ciency rather than on-body location, given

Polarization and Pattern Diversity-Based Dual-Feed Planar Inverted-F Antenna

This work presents a novel dual-feed planar inverted-F antenna (PIFA) suitable for wireless applications such as wireless local area network (WLAN) and long term evolution (LTE) as a diversity and multiple-input multiple-output (MIMO) antenna. Instead of two antenna elements, there is only one top radiating element with two isolated feeding ports which can save space and cost. The two feed plates are placed perpendicular to each other to exploit both the polarization diversity and pattern diversity. The isolation between the two antenna ports is achieved by modifying the ground plane under the top radiating element. Simulated and measured results are obtained to verify the conclusion .

Time variant source resistance in the THz photoconductive antenna

Terahertz (THz) photoconductive antennas are the most common devices for the generation and detection of THz waves. One of the main problems of the current photoconductive antennas as the emitter is that the optical-THz conversion efficiency is very low, thus it is difficult to obtain high power THz radiation. Impedance mismatching between the antenna and the photoconductive material (which acts as the source impedance) is one of the primary factors on this low conversion efficiency. In order to assess this issue, proper evaluation of the resistance of the photoconductive material is required. In this paper, the time dependant conductivity of the photoconductive material based on pulsed system is first calculated. Then, through this conductivity, the source conductance (resistance) in THz photoconductive antenna is determined which illustrates influences of different parameters of laser pulses, photoconductive material properties and THz antenna. This new formula can aid in a better theoretical assessment as part of total optical-THz conversion efficiency calculation as the source conductance (resistance) can be more accurately derived.

Repeatability and uncertainty evaluations of on-body textile antenna efficiency measurements in a Reverberation Chamber

For the validation of body worn antennas, the human body should be taken into account as the performance of such antennas is likely to differ from their free space equivalents. How best to determine the human body effects on antenna performance is a pertinent point in which many questions still remain. In this paper we consider the efficiency of some newly developed textile antennas for on-body applications and directly establish that a Reverberation Chamber (RC) is an ideal solution for these types of measurements in conjunction with human beings. It is shown that a RC can provide a very repeatable series of measurements in conjunction with the human (in the order of 3%), proving that inevitable (slight) human movements do not affect the measurements accuracy, and further, that the on-body efficiency can be assessed with a low uncertainty (~ 0.22 dB) if the correct procedure is followed. The work proves that the RC facility is beneficial to any institution who seeks this knowledge for their designs.

THz photoconductive antennas in pulsed systems and CW systems

In designing terahertz (THz) antennas with high output power and/or high optical-THz conversion efficiency, the photoconductor property is an important consideration. According to the type of the optical excitation, THz antennas can be divided into two categories: THz photoconductive antennas in a pulsed system and THz photomixing antennas in a Continuous-Wave (CW) system. How different excitation types can affect the performance of the antenna is an important issue in THz systems. Thus, the aim of this paper is to investigate and compare THz photoconductive antennas and THz photomixing antennas from an important design parameter point of view; namely the conductance of the photoconductive material substrate which acts as the source for a PC antenna. Through numerical analyses of example systems, it is shown that source resistance of a THz antenna in a CW system is greater than those in a pulsed system. Further, an important practical system setting, the dependency of alignment of two beams in CW systems on antenna gap size is also investigated. It is illustrated that mixing efficiency for large gap antennas is more sensitive to angle between two beams.

Ground plane effects and measurements of portable planar broadband antennas

This paper deals with two of the most important and difficult aspects of portable planar broadband antennas: the ground plane effects and measurements. To minimize the ground plane effects, optimized slots are created on the ground plane to limit the current flow hence the ground plane effects, which is demonstrated to be a simple but effective approach. For the antenna measurement, our focus is on how to measure the antenna radiation efficiency accurately and efficiently. Two of the latest methods, reverberation chamber and source stirred chamber/cap methods, are employed and discussed. Both numerical and experimental results are presented to aid our analyses and discussions.