Academic literature on the topic 'Antennas - Bandwidth'

The physical size and material properties of antennas are major limiting factors of the antennas performance. These limitations are usually manifested through parameters such as bandwidth, quality factor and efficiency. The presented research examines these fundamental limitations with specific focus on electrically small antennas, and a new bound for antenna efficiency is developed.<br>Thesis (PhD Doctorate)<br>Doctor of Philosophy (PhD)<br>Griffith School of Engineering<br>Science, Environment, Engineering and Technology<br>Full Text

Thesis (Ph.D.)--City University of Hong Kong, 2005.<br>"Submitted to Department of Electronic Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy" Includes bibliographical references (leaves 152-162)

Reconfigurable antennas represent a recent innovation in antenna design that changes from classical fixed-form, fixed-function antennas to modifiable structures that can be adapted to fit the requirements of a time varying system. Advances in microwave semiconductor processing technologies have enabled the use of compact, ultra-high quality RF and microwave switches in novel aspects of antenna design. This dissertation introduces the concept of reconfigurable antenna bandwidth control and how advances in switch technology have made these designs realizable. Specifically, it details the development of three new antennas capable of reconfigurable bandwidth control. The newly developed antennas include the reconfigurable ring patch, the reconfigurable planar inverted-F and the reconfigurable parasitic folded dipole. The relevant background work to these designs is described and then design details along with computer simulations and measured experimental results are given.<br>Ph. D.

In this thesis a technique that is being used in another area of technology to optimize light reception in a photographic camera was also applied to the dielectric resonator antenna. The technique consisting of the use of thin film to couple the media and camera impedances resulted in a dielectric resonator antenna bandwidth enhancement technique. The bandwidth enhancement technique was found when thin film dielectric layer structure was used to couple the dielectric resonator and its feed mechanism. Remarkable good performance was detected with a coplanar waveguide fed cylindrical dielectric resonator antenna which resulted in an improvement to its fractional bandwidth from 7.41% to 50.85%. Extensive experimental work was undertaken in order to explore the extent offered in bandwidth performance by using thin film dielectric layer structure in the dielectric resonator antenna performance. The experimental tasks were designed in order to investigate the influence of the thin film dielectric layer structure in relation to its size, shape, thickness, position and direction. Experimental results were supported with simulation work with the computer simulation technology microwave studio. The pieces of the material used for undertaking this experimental work were manually handcrafted. Four different dielectric resonator antenna designs were used in order to carry out the experimental work including the coplanar waveguide fed cylindrical dielectric resonator antenna. The other three dielectric resonator antennas were implemented using the same microstrip feed mechanism. Improved performance in bandwidth was achieved for all the designs. Optimization of the incoming signal was observed when a piece of thin film dielectric layer structure was placed in position between the feed mechanism and the dielectric resonator antenna. The optimization was observed as an enhancement in both the return loss level and the bandwidth of work. Different unexpected operational modes from were activated, such modes being called perturbed modes. Two different shapes were used in this project. Cylindrical dielectric resonator antenna (ɛr = 37) from a commercial provider and two novel rectangular dielectric resonator antennas. The novel rectangular dielectric resonator antennas were created with the methodology presented in this thesis. The rectangular dielectric resonator antennas were elaborated with transparent ceramic material (ɛr = 7) and TMM10i (ɛr = 9.8) from the Rogers Corporation company. The bandwidth enhancement technique was tested in novel embedded dielectric resonator antennas. A coplanar waveguide fed embedded cylindrical dielectric resonator antenna achieved a maximum bandwidth enhancement of 156.77% around f = 3.79 GHz with a thin film dielectric layer structure modified rectangular piece on one edge. Escalation to dielectric resonator antenna design at millimeter wave frequencies was achieved by using thin film dielectric layer structure bandwidth enhancement technique and a handcrafted printed circuit board millimeter wave feed mechanism. The millimeter wave feed mechanisms were achieved using a low cost alternative technique conceived as part of this project. Millimeter wave dielectric resonator antennas were implemented using thin film dielectric layers structure. The antennas deliver an adequate performance in bandwidth. The work presented in this thesis demonstrates dielectric resonator antenna simpler geometry, simple couple schemes, small size, low profile, light weight, and ease of excitation and orientation. Other parameters have also been investigated covering reduced complexity, high degree of flexibility, ease of fabrication and the use of low cost technology to escalate to millimeter wave frequencies.

Abstract In this thesis, bandwidth (BW) enhanced antennas for mobile terminals and multilayer ceramic packages are presented. The thesis is divided into two parts. In the first part, electrically frequency-tunable mobile terminal antennas have been studied. The first three antennas presented were of a dual-band planar inverted-F type (PIFA) and were tuned to operate in frequency bands appropriate to the GSM850 (824–894 MHz), GSM900 (880–960 MHz), GSM1800 (1710–1880 MHz), GSM1900 (1850–1990 MHz) and UMTS (1920–2170 MHz) cellular telecommunication standards with RF PIN diode switches. The first antenna utilized a frequency-tuning method developed in this thesis. The method was based on an integration of the tuning circuitry into the antenna. The tuning of the second antenna was based on a switchable parasitic antenna element. By combining the two frequency-tuning approaches, a third PIFA could be switched to operate in eight frequency bands. The planar monopole antennas researched were varactor-tunable for digital television signal reception (470–702 MHz) and RF PIN diode switchable dual-band antenna for operation at four cellular bands. The key advantage of the former antenna was a compact size (0.7 cm3), while for the latter one, a tuning circuit was implemented without using separate DC wiring for controlling the switch component. The second part of the thesis is devoted to multilayer ceramic package integrated microwave antennas. In the beginning, the use of a laser micro-machined embedded air cavity was proposed to enable antenna size to impedance bandwidth (BW) trade-off for a microwave microstrip in a multilayer monolithic ceramic media. It was shown that the BW of a 10 GHz antenna fabricated on a low temperature co-fired ceramic (LTCC) substrate could be doubled with this technique. Next, the implementation of a compact surface mountable LTCC antenna package operating near 10 GHz was described. The package was composed of a BW optimized stacked patch microstrip antenna and a wide-band vertical ball grid array (BGA)-via interconnection. Along with the electrical performance optimization, an accurate circuit model describing the antenna structure was presented. Finally, the use of low-sintering temperature non-linear dielectric Barium Strontium Titanate (BST) thick films was demonstrated in a folded slot antenna operating at 3 GHz and frequency-tuned with an integrated BST varactor.

Electrically small, low profile antennas have become the new frontier in wireless communication research. With the pressure to miniaturize wireless communication devices, engineers are turning to small low profile antennas as a way to reduce their antennas and hence their devices. Ideally, one would also like to at least maintain antenna bandwidth and efficiency while reducing size. However, in theory, antenna performance degrades when it is miniaturized—impedance bandwidth decreases with the reduction in antenna size. This thesis investigates the possibility of increasing the input impedance bandwidth without enlarging the volume of the antenna. This thesis attempts to break the fundamental tradeoff between antenna size and bandwidth by loading it with a nonlinear element. First, a brief summary of antenna background definitions is presented. Next, the analytical framework of the thesis is presented using a model of a narrowband antenna. A literature review of various narrowband electrically small antennas is studied, including the pros and cons of the Inverted-F antenna (IFA), Inverted-L antenna (ILA), and the Planar Inverted-F antenna (PIFA).Next, the analysis and the methodology leading to results are discussed and simulated results are presented. Simulated results show that the PIFA is able to achieve a higher bandwidth with a loaded nonlinear element. However, it is difficult to sustain the efficiency of the antenna due to harmonics generated by nonlinearity in the antenna. Results indicate that an increase in nonlinearity tends to generate harmonics which leads to losses in the antenna.<br>Master of Science

The research work explored the fundamental ideas and techniques required to design an antenna placed on different common target objects for radio frequency identification. This was achieved by studying the effect of antenna conductivity in a wide range and the substrate relative permittivity from 1 to 10. The effect on wire meander antenna properties are different to that for a straight linear dipole antenna; the increase in wire radius of the meander antenna increases the resonant frequency but increases in wire radius of a straight dipole antenna decreases the resonant frequency. This study concluded that the approximate antenna bandwidth needed for common target object materials is 28.5%. A genetic algorithm GA code was written to optimize the meander antenna structure to obtain a larger bandwidth. The GA optimized each vertical element and horizontal element for radius and length. The optimized antenna has 14.5% bandwidth which covers the entire UHF RFID frequency. As conductivity is not changed further, the properties of antennas on ungrounded substrates with different permittivity and thickness were investigated. The solution for this problem involved transforming a circular cross section wire antenna structure to a planar strip antenna structure. A number of theoretical approaches were assessed to solve for the effective permittivity when the substrate material is thin. Surface impedance and slab waveguide propagation techniques were compared to a capacitive solution and an insulated wire antenna. The insulated wire method gives most accurate results (< 3.5% error) and was verified using numerical modelling and experimental work. Measurements on a planar straight dipole on FR4 (fc = 1.50GHz) compare favourably with the antenna modelled without the substrate and scaled using the insulated wire technique at (fc = 1.49GHz).<br>Thesis (PhD Doctorate)<br>Doctor of Philosophy (PhD)<br>Griffith School of Engineering<br>Science, Environment, Engineering and Technology<br>Full Text

Many bandwidth enhancement techniques for microstrip patch antennas have been developed since the 1970's. Except for an IEEE collection of reprints which appeared in 1995, relatively little work has been done to review and categorize these techniques. As a result, the published research and design of broadband microstrip antennas has become somewhat unsystematic. In this thesis, papers on broadband microstrip antennas have been reviewed. Using full-wave electromagnetic simulation, the important performance parameters such as the bandwidth, realized gain, antenna efficiency, radiation efficiency and radiation patterns of broadband microstrip patch antennas have been considered. Based on these results, bandwidth enhancement techniques have been categorized in two broad classes, namely those applicable when electrically-thick low-permittivity substrates are used, and those applicable to electrically-thin high-permittivity substrates. These broad classes have been sub-divided into several sub-classes in a structured manner that aids the understanding of the bandwidth enhancement methods. A summary of these techniques, linked to a comparison of resulting microstrip patch antenna performance obtained from full-wave analysis of the sub-classes, is provided. It is also shown, through a specific example, how the increased understanding afforded by this categorization can lead to the development of new broad bandwidth geometries that can offer some advantages over existing ones.