S. J. Boyes

A monopole water antenna

A monopole water antenna with a relative permittivity of 81 and a variable conductivity has been studied. Three issues are addressed in the paper. Firstly, the relationship between the conductivity and antenna radiation efficiency is investigated. Secondly, a new feeding design for the water antenna is proposed and a good return loss, radiation efficiency and radiation pattern are obtained. Thirdly, experiments are conducted in anechoic and reverberation chambers to evaluate its performance. Good agreements are achieved between the simulation and measurement results. With different conductivity, the antenna may be regarded as a dielectric resonant antenna, a conducting antenna or their combination. This type of antenna can be considered as an attractive alternative to conventional antenna for various applications.

Wideband antenna efficiency measurements

Over the past 10 years or so, many broadband and ultra-wideband antennas have been developed for broadband high data rate mobile communications. It is realized how to make efficient and accurate measurements for such antennas could be a challenging issue. In this paper, we examine the antenna efficiency measurement techniques which have been used up to now, and identify their advantages and disadvantages for broadband measurements. It is shown that the classic Wheeler cap method, which is the best for electrically small antennas, has a lot of attractive features even for broadband antenna measurements in terms of the cost and efficiency although the newly proposed reverberation chamber method may become a good alternative method. A “source stirred” method is proposed as a new approach for the broadband antenna efficiency measurement and its major advantages are cheap, convenient, and efficient. Both the experimental and numerical results are provided. It is shown that the loss due to the imperfection of the cavity can cause a serious problem for obtaining an accurate result. How to eliminate the effects of the cavity loss and improve the measurement accuracy for this method is an issue to be resolved.

An elliptical UWB monopole antenna with reduced ground plane effects

Many monopole UWB antennas have been developed over the years. One common problem is that their performance is heavily affected by the ground plane. In this paper, a new approach on how to reduce the ground plane effects on such antennas is proposed: L-shape cuts on the edge of the ground plane are introduced and it is shown that this method changes the current distribution on the ground plane without sacrificing the frequency and time domain performance, which makes such antennas more suitable for real applications with different sizes of the ground plane.

An UWB planar inverted-F antenna for wireless applications

The planar inverted-F antenna (PIFA) is widely used in mobile and portable radio systems due to its excellent features. However, it is not yet employed as an ultra wide band antenna because it was considered a narrowband antenna. This paper introduces an ultra wideband planar inverted-F antenna based on three techniques, which are (a) changes in the widths of feed and shorting plates, (b) addition of an inverted-L shaped parasitic element and (c) addition of a rectangular parasitic element. It is shown that ultra wideband PIFAs with fractional bandwidth of more than 100 % is achieved covering from 3.4 GHz to 10.7 GHz. Simulated and measured results are provided to verify the conclusion.

Band-Notched Ultrawide Band Planar Inverted-F Antenna

A novel ultrawide band planar inverted-F antenna with band-notched characteristics is presented in this paper. The planar inverted-F antenna uses two parasitic elements to enhance the bandwidth to cover the ultrawide band. The band-notched feature is added by inserting a W-shaped slot on the top radiating element of the antenna with a band rejection from 5.08 to 6 GHz (measured). Both the measured and simulated results are obtained to draw the conclusions.

Improved Rayleigh field statistic in reverberation chambers from modified mechanical stirring paddles

This paper introduces a novel modification to the design of mechanical stirring paddles in reverberation chambers. The work focuses on lower modal densities with a view to increasing the overall effectiveness of the mechanical stirring operation in this range from a statistical perspective. The research indicates that by cutting tapered slots into the stirrer plate, the induced surface current can be enticed to interact more with the stirrer giving rise to an improved non line of sight field statistic. The intuitive nature of the design means that the slots would be simple, easy and cost effective if implemented into existing chambers. The performance facets have been achieved for no extra increase in the physical stirrer dimensions which means that the potential working volume of the chamber can remain as large as possible. A potential benefit therefore exists for the antenna measurement community who employ reverberation chambers as their measurement facility.

Comparison of diversity gain performance of single element dual-feed PIFAs with assorted MIMO antennas

Planar Inverted F Antennas (PIFAs) are commonly used in portable applications due to their attractive features. There exists a huge demand to use these PIFAs as MIMO or diversity antennas to allow for an increase in data rates or signal quality and to combat the shallow fading minima that exist in a multipath propagation environment with a non line of sight path. Recently, two new single element dual feed PIFAs have been developed at Liverpool; but are mainly investigated theoretically and numerically with limited experimental results. This paper presents a further study of these antennas; in particular, the diversity gain is measured using a large reverberation chamber, and the results are compared to some other MIMO/diversity antennas reported in literature. Furthermore, the trade-off between the miniaturisation and diversity gain is also investigated. It is also shown that a 24% increase in diversity gain can be achieved using cross-polarised feeding as compared to a co-polarised fed configuration.