Multimode dielectric resonator antenna of very high permittivity

In this paper a design strategy to obtain low loss, small size dielectric antennas, by using very high dielectric constant materials is described. It is shown how by properly selecting the resonator shape and combining different resonant modes it is possible to design dielectric resonator antennas (DRA) with compact size and wide frequency coverage even at the cellular frequencies. Simple formulas are presented to illustrate the design procedure and allow a quick dimensioning of the antenna. Furthermore the paper describes techniques to enhance the response provided by the natural resonance frequencies of DRA, by adding parasitically coupled conducting strips, to enable multi-band operation. Results and examples are reported, showing the effectiveness of the proposed technique.

Introduction

High dielectric constant materials have been widely used in the past to build antennas with reduced size. Dielectric resonator antennas, in particular, provide high efficiency, small size and simple feeding schemes [1], [2]. While these features can be fully exploited when the frequencies of operation are of the order of several gigahertz or higher, they have limited use at the cellular frequencies. To obtain a reasonable antenna size in such bands, very high dielectric constant would be required, thus resulting in an unacceptable reduction in bandwidth. As the dielectric constant increases, in fact, the Q of the antenna increases as [3], leading to very narrow band behavior. This paper describes how to improve the bandwidth of a DRA, while using a dielectric constant high enough to achieve the desired limited size. Two concurrent approaches have been proven to be effective in this respect. The first one focuses on selecting a resonator shape that minimizes the surface-to-volume ratio, and hence to the resonator Q.