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ABSTRACT
Dielectric resonators are parts made of insulating ceramic material with high permittivity. They are used to replace microwave cavities, and to reduce their volume. Like them, they confine electromagnetic waves (up to 95% of the energy) in the part with the resonance mode TE1d. This article introduces RLC resonant circuits, microwave cavities, and transition to the resonators with the coupling modes. The quality factors for cavities and dielectric resonators are obtained from resonance linewidth measurements by transmission or absorption filters. Other dielectric-loaded cavity modes allow a reduction in volume of multi-pole filters or an increase in frequency, such as TM, HEM, and TEM modes, or gallery modes.
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Pierre FILHOL: Design engineer - EXXELIA TEMEX PESSAC FRANCE
INTRODUCTION
Dielectric resonators are objects made of insulating material, based on oxides, in the form of bare or metallized ceramic, cylinder disk, cube, sphere... They are used as resonators (components) in the realization of filters, oscillators, antennas, at microwave frequencies (between a few tens of megahertz (10 6 Hz) and a few tens of gigahertz (10 9 Hz).
The dielectric resonator replaces empty resonant cavities (air only) and, like them, confines electromagnetic energy, thanks to its high permittivity (between 10 and 100). It has resonant natural frequencies (modes), with the following advantages over resonant cavities:
reduction in component size in the ratio of the square root of the permittivity,
adjustable coefficient of thermal stability of the resonance frequency of around 10 –6 /°C, enabling it to adapt to its environment,
ease of use.
Depending on material composition and environment, the quality factor can be higher than that of a metal cavity, with the exception of a superconducting cavity.
Even if, in practice, the dielectric resonator is easy to use, the theoretical determination of the component's resonant frequency or quality factor is more complex than that of a metal cavity. Numerical calculation techniques have made it possible to overcome this difficulty.
This article describes the concept of the TE 01δ electric transverse-mode resonator and its characterizations by material manufacturers. The way in which it is coupled to the external circuit with various elements (loop, microstrip line) is outlined. Characterization of the resonator as a filter element allows us to trace the material's dielectric losses. Dielectric resonator materials are also used in different modes (hybrid, transverse magnetic TM, transverse electromagnetic TEM, etc.). These latter modes are used in the case of filters (space, mobile radio): the aim is generally to achieve a compromise between the highest possible quality factor and the minimum volume or mass of the resonator.
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KEYWORDS
cavities | resonators | microwaves | resonance's quality factor
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Dielectric resonators
RLC resonant circuits
Bibliography
Directory
University of Limoges-XLIM – http://www.xlim.fr/minacom
LEEDS University – Faculty of Engineering – http://www.leeds.ac.uk
Statistical and economic data
The main applications are dielectric resonator filters for radio telephone base station applications, oscillators for alarms, direct reception of satellite television, and general military or space telecommunications. Figures can be found in the article
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