Linearly and circularly polarized conformal strip-fed dielectric resonator antennas (DRAs) are studied in this article. In the latter case, a parasitic patch is used to excite a nearly degenerate mode. The hemispherical DRA, excited in its fundamental broadside TE111 mode, is used for the demonstration. In the analysis, the mode-matching method is used to obtain the Green's functions, whereas the method of moments is used to solve for the unknown strip currents. In order to solve the singularity problem of the Green's functions, a recurrence technique is used to evaluate the impedance integrals. This greatly increases the numerical efficiency. Measurements were carried out to verify the calculations, with good results.


Keywords:

circularly polarized antenna;
dielectric antennas;
mode-matching methods;
moment methods;
parasitic antennas;
resonance

Dielectric Resonator Antennas

Theoretical and experimental investigations on rectangular dielectric resonator antennas having a value of /spl epsiv//sub r/, in the range of 10 to 100 are reported. The resonant frequencies and radiation Q-factors of the lowest order "magnetic-dipole" modes are derived on the basis of a first-order theory. The accuracy of the model in predicting the resonant frequency and radiation Q-factor is verified by comparison with results of a rigorous theory and experiments. Various feeds for the antennas such as probe, microstrip slot, and microstrip line are described. Measured radiation patterns are shown and the effect of feed and mode degeneracy on the cross-polarisation levels is discussed.

Theoretical and experimental investigations on rectangular dielectric resonator antennas

The concept of a novel reactive impedance surface (RIS) as a substrate for planar antennas, that can miniaturize the size and significantly enhance both the bandwidth and the radiation characteristics of an antenna is introduced. Using the exact image formulation for the fields of elementary sources above impedance surfaces, it is shown that a purely reactive impedance plane with a specific surface reactance can minimize the interaction between the elementary source and its image in the RIS substrate. An RIS can be tuned anywhere between perfectly electric and magnetic conductor (PEC and PMC) surfaces offering a property to achieve the optimal bandwidth and miniaturization factor. It is demonstrated that RIS can provide performance superior to PMC when used as substrate for antennas. The RIS substrate is designed utilizing two-dimensional periodic printed metallic patches on a metal-backed high dielectric material. A simplified circuit model describing the physical phenomenon of the periodic surface is developed for simple analysis and design of the RIS substrate. Also a finite-difference time-domain (FDTD) full-wave analysis in conjunction with periodic boundary conditions and perfectly matched layer walls is applied to provide comprehensive study and analysis of complex antennas on such substrates. Examples of different planar antennas including dipole and patch antennas on RIS are considered, and their characteristics are compared with those obtained from the same antennas over PEC and PMC. The simulations compare very well with measured results obtained from a prototype /spl lambda//10 miniaturized patch antenna fabricated on an RIS substrate. This antenna shows measured relative bandwidth, gain, and radiation efficiency of BW=6.7, G=4.5 dBi, and e/sub r/=90, respectively, which constitutes the highest bandwidth, gain, and efficiency for such a small size thin planar antenna.

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Antenna miniaturization and bandwidth enhancement using a reactive impedance substrate

This article presents a historical review of the research carried out on dielectric resonator antennas (DRAs) over the last three decades. Major research activities in each decade are highlighted. The current state of the art of dielectric-resonator-antenna technology is then reviewed. The achievable performance of dielectric resonator antennas designed for compactness, wide impedance bandwidth, low profiles, circular polarization, or high gain are illustrated. The latest developments in dielectric-resonator-antenna arrays and fabrication techniques are also examined.

Dielectric Resonator Antennas: A Historical Review and the Current State of the Art

This paper features some of the advances in dielectric-resonator antenna technology at the Communications Research Centre. Several novel elements are presented that offer significant enhancements to parameters such as impedance bandwidth, circular-polarization bandwidth, gain, or coupling to various feed structures. Several linear and planar arrays are also presented, to illustrate the performance of dielectric-resonator antenna elements in the array environment.

Recent advances in dielectric-resonator antenna technology

A dielectric resonator antenna system is disclosed wherein a dielectric material having a high dielectric constant is placed between a dielectric resonator antenna (DRA) and the antenna feed. Preferably the dielectric material having a high dielectric constant is either in the form of an insert within a cavity of the DRA or alternatively is in the form of a thin layer between the feed and the DRA for enhancing coupling therebetween. It is preferred that the high dielectric constant material be at least twice the value of the dielectric resonator antenna.

Broadband nonhomogeneous multi-segmented dielectric resonator antenna system

A circularly polarised dielectric resonator antenna is reported. The circular polarisation is obtained by exciting the two orthogonal HE/sub 11 delta / modes of a cylindrical ring dielectric resonator in phase-quadrature. Measured results show that the antenna has an axial ratio of less than 3 dB over a beam width of 100 degrees with a minimum value of approximately 0.5 dB in this range. >

Circularly polarised dielectric resonator antenna

Recently, dielectric resonator antennas (DRA) have been proposed as an alternative to the popular microstrip patch. Since then, research has continued, extending their performance capabilities and confirming their potential as low profile and efficient antenna elements for array applications. Also a single-point fed dielectric resonator antenna has been reported, capable of radiating a circularly polarized signal with a much wider axial ratio bandwidth than a similar single-point fed microstrip patch. Further capability enhancements of a dielectric resonator antenna have recently been demonstrated by fabricating the antenna from ferrite material. With a properly biased static magnetic field, it has been shown to possess frequency tuning and polarization diversity properties. The purpose of this paper is to present a novel development of a DRA which possesses a much wider operational bandwidth than previously reported. This improvement can be accomplished with a simple slot feed and without an elaborate matching circuit or a complicated stacking procedure which is generally required by the microstrip patch.

An investigation of a novel broadband dielectric resonator antenna

A closed form expression is derived for the radiation Q-factor of a rectangular dielectric resonator (DR) antenna. The method used for determining the Q-factor is based on replacing the DR by a polarization electric current source. Experiments were conducted on dielectric resonators having a value of /spl epsi//sub r//spl ap/38 to verify the accuracy of the expression. The measured results are found to be in fairly good agreement with theory. >

D.J. Roscoe

Papers

Recent advances in dielectric-resonator antenna technology

Broadband nonhomogeneous multi-segmented dielectric resonator antenna system

Circularly polarised dielectric resonator antenna

An investigation of a novel broadband dielectric resonator antenna

Radiation Q-factor of rectangular dielectric resonator antennas: theory and experiment