Browse Prior Art Database

DOUBLE-COAXIAL RESONATOR FILTER

IP.com Disclosure Number: IPCOM000007436D
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2002-Mar-26
Document File: 2 page(s) / 106K

Publishing Venue

Motorola

Related People

Peter Vizmuller: AUTHOR

Abstract

This new, compact UHF filter combines excel- lent electrical performance with single-axis assem- bly; it is an integral part of the UHF Quantar/Quantro base station receiver module. The filter is easy to tune, its center frequency is stable under vibration and over temperature variations, and the filter is free ofspurious responses up to 2.5 GHz.

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MolylRoLA Technical Developments

DOUBLE-COAXIAL RESONATOR FILTER

by Peter Vizmuller

INTRODUCTION DOUBLE-COAXIAL RESONATORS

  This new, compact UHF filter combines excel- The double-coaxial structure is formed by includ- lent electrical performance with single-axis assem- ing a capacitive cap at the top of a conventional coax- bly; it is an integral part of the UHF Quantar/Quantro ial resonator, forming three interconnected trans- base station receiver module. The filter is easy to mission lines, as shown in the figure below together tune, its center frequency is stable under vibration with the design equations-the resonant frequency and over temperature variations, and the filter is free is the Frequency at which Z, or Zc approach infinity. ofspurious responses up to 2.5 GHz.

IYPEDANCE AT TOP z, tongt, + zp tan&+ z3 tql~

OF RESONATOR Zn=j

' -$ ton,6l3 (z, tonp-t, + z2 tqq

  The resonator rod is hollow at the top, in order to accept a tuning screw. The depth ofthe hollowed- out portion is such that the tuning screw shorts out the resonator, when it is threaded all the way in-this makes the tuning algorithm very simple and effective.

FILTER CONSTRUCTION

  The above resonators are coupled to each other by conventional apertures to realize a Butterworth or Chebyshev response. The real difficulty arises when implementing the input and output coupling con- nections. A direct wire connection between an RF connector and a tap on the resonator rod results in manufacturing difftculties, because the RF connec-

tor and resonator rods reside on different parts of the mechanical assembly, thus preventing a single- axis manufacturing process. This difficulty can be avoided by an arrangement shown in the following cross-section, where a wire from the RF connector is connected to the center portion ofa double-aperture opening, thus forming two magnetic coupling loops. The magnetic f...