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A NOVEL TUNING METHOD FOR DIELECTRIC RESONATORS

IP.com Disclosure Number: IPCOM000007477D
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2002-Mar-29

Publishing Venue

Motorola

Related People

Kenneth V. Buer: AUTHOR

Abstract

This paper presents a novel technique for the tun- ing of high dielectric resonators at microwave and mil- limeter wave frequencies. The resonator is tuned by coupling it to a section of non-resonant microsirip line. An experimental band-rejectfilter with a Q of 550 was tuned using this technique. The resulting tuning range of theJilter was over 18 times its bandwidth. This tech- nique makes it cost effective to tune dielectric resona- tors over a relatively broad range while maintaining a high Q characteristic.

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MoIy)RoLA Technical Developments

A NOVEL TUNING METHOD FOR DIELECTRIC RESONATORS

by Kenneth V. Buer

ABSTRACT

  This paper presents a novel technique for the tun- ing of high dielectric resonators at microwave and mil- limeter wave frequencies. The resonator is tuned by coupling it to a section of non-resonant microsirip line. An experimental band-rejectfilter with a Q of 550 was tuned using this technique. The resulting tuning range of theJilter was over 18 times its bandwidth. This tech- nique makes it cost effective to tune dielectric resona- tors over a relatively broad range while maintaining a high Q characteristic.

I. INTRODUCTION

  The expanding use of microwave and mm wave frequencies in commercial satellite, mobile commu- nication, and consumer products, calls for size, weight, and cost reduction in microwave and mm wave filtering. In applications where performance requirements dictate a high Q implementation, die- lectric resonator filters are a welcome alternative to waveguide filters. Dielectric resonators can achieve unloaded quality factors (Qo) comparable to waveguide resonators, but at a substantially lower weight and smaller volume. Dielectric resonators are also compatible with a microstrip environment, which eliminates the need for microstrip to waveguide

adapters. In theory, the resonant mode and the dimen- sions of the dielectric resonator along with the rela- tive dielectric constant (E,) completely determine the resonant frequency (f,)[l]. In practice, however, the exact in-circuit resonant frequency can not be accurately predicted due to thermal expansion, and the dimensional tolerances of both the resonator and its placement in the circuit. Therefore, some type of tuning is generally required to attain the desired frequency response.

  One traditional method for tuning dielectric res- onators employs a tuning screw or dielectric slug which can be brought in close proximity of the res- onator to perturb the electric lieldll]. The tuning screw or slug simply adds some shunt capacitance to the resonator, causing a slight downward shifl in resonant frequency. At frequencies above about 20 GHz, the mechanical tolerances required for accu- rately tuning a dielectric resonator by this traditional method get extremely tight, making this approach impractical for low cost high volume production.

  Optical and magnetic techniques have also been suggested [1,4] to tune dielectric resonator oscilla- tors. These methods can be adapted to filtering appli- cations, but they add a significant amount of com- plexity and cost.

Fig. 1 A Dielectric Resonator Coupled to a Microstrip Line

0 M",orola. Inc. ,995 122 July 1995

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MOlWR0L.A Technical Developments

  A simpler approach is to use a resonant microstrip structure coupled to the dielectric reso- nator. An example of this type of tuning has been reported by Farr[4] in which the microstrip tuning structure was plac...