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NOVEL MICROSTRIP FILTER STRUCTURE

IP.com Disclosure Number: IPCOM000005635D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2001-Oct-23
Document File: 1 page(s) / 74K

Publishing Venue

Motorola

Related People

Jerry Meyerhoff: AUTHOR

Abstract

Conventional microstrip bandpass filters need large open areas over their resonators to avoid detuning effects and to maintain their inter-resonator coupling factors. They typically exhibit only modest stop band and attentuation characteristics. Furthermore, they are tuned by irreversably removing portions of the metallization or by expensive high Q trim capacitors: processes which are both slow and costly. Typically, filters for different parts of a system cannot share a common small substrate due to stray coupling effects.

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MO7OROLA Technical Developments Volume 7 October 1987

NOVEL MICROSTRIP FILTER STRUCTURE

by Jerry Meyerhoff

   Conventional microstrip bandpass filters need large open areas over their resonators to avoid detuning effects and to maintain their inter-resonator coupling factors. They typically exhibit only modest stop band and attentuation characteristics. Furthermore, they are tuned by irreversably removing portions of the metallization or by expensive high Q trim capacitors: processes which are both slow and costly. Typically, filters for different parts of a system cannot share a common small substrate due to stray coupling effects.

   The structure shown in Figure 1 solves many of the shortcomings of conventional microstrip bandpass filters. Each quarter wave resonator (1) has been foreshortened by the expansion of a capacitive hat (2) at the high impedance end of the transmission line. The hat also provides a target for grounded tuning disc (3) to form a simple parallel plate variable capacitor. This allows easy repeatable shifts in the individual resonator frequencies.

   Resonators are arranged in pairs to form 2-pole filt~ers (4) in a common shield compartment. The shield has an integral aperature (5) which reduces the coupling coefficient between resonator pairs, Unlike conven- tional designs, this allows the resonators to be more densely situated.

The aperatures also modify the fields above the resonator to significantly reduce the detuning effect of the cover...