Browse Prior Art Database

MICROSTRIP NOTCH FILTER

IP.com Disclosure Number: IPCOM000008035D
Original Publication Date: 1997-Mar-01
Included in the Prior Art Database: 2002-May-14
Document File: 1 page(s) / 53K

Publishing Venue

Motorola

Related People

Paul Dahl: AUTHOR

Abstract

In two way radio communication products, har- monics of the transmitted frequency are generated that are undesirable. The microstrip notch filter described here is able to suppress undesired har- monics. It has sharper attenuation than other com- monly used microstrip filters. This device can be designed to filter out any particular harmonic for a narrow band device.

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MOTOROLA Technical Developments

MICROSTRIP NOTCH FILTER

by Paul Dahl

  In two way radio communication products, har- monics of the transmitted frequency are generated that are undesirable. The microstrip notch filter described here is able to suppress undesired har- monics. It has sharper attenuation than other com- monly used microstrip filters. This device can be designed to filter out any particular harmonic for a narrow band device.

  This narrow band notch filter can be fabricated in either micro-strip or stripline. The notch in the simulated filter was wide enough to filter out the second harmonic of a 900 MHz radio across the band of the radio. The filter works by coupling the energy of the desired harmonic out of the transmis- sion line into a resonator and then coupling this

energy from the resonator back into the transmis- sion line 180 degrees out of phase.

  The filter consists of a transmission line that has a u-bend so that the transmission line doubles back and runs parallel to itself. The microstrip res- onator is placed between the parallel segments of the transmission line. See attached figure. The res- onator is 0.5 wavelength long at the filtered fre- quency. The transmission line is one wavelength long from where it leaves the resonator to where it encounters it again. These measurements ensure coupling out of phase at the suppressed frequency. At the pass band there is very little degradation of the signal.

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