# Microstrip Tapped Line Filter Design - RF Cafe Forums

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Antonio
Post subject: Microstrip Tapped Line filter Design Posted: Fri Jun 29, 2007 5:31 am

Captain

Joined: Sat Jun 16, 2007 12:26 am
Posts: 12
Hi All,

Can you tell me how to find out the tapped point and tapped length in a Edge coupled tapped line filter design?

I am trying to design a band pass filter using Edge coupled tapped line structure.

The inputs I have are impedances, Er, substrate information. I am not able to find out the way to calculate tapped point and tapped length using all these inputs.

Is there any way to find out the tapped length and tapped point using ADS tool? If it is then how?

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trobbio
Post subject: Posted: Sat Jan 03, 2009 1:39 pm

Lieutenant

Joined: Fri Jan 02, 2009 12:27 pm
Posts: 1
Search for an IEEE article titled "Microstrip Tapped-Line Filter Design" by Joseph S. Wong. That article gives the design procedure and all the math behind selecting the tap point.

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nubbage
Post subject: Posted: Tue Jan 06, 2009 12:09 pm

General

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
If you cannot locate that, a simple high-level approach is to set the internal impedance level of the filter (say 200 ohms or whatever), which can improve the design process. Then the tapping point is simply derived from the ratio of internal and external (50 ohm) impedance, the end-line characteristic Z, and the loaded Q of the input/output resonators. The formula is

tap point = Len * ASIN(SQRT(PI*Zs/(4*Z0*Ql)))

where len is the length of the end resonator,
Zs is the internal impedance (100 ohm, 200 ohm or whatever)
Z0 is the characteristic impedance of the end resonator in its geometric environment
and Ql is the loaded Q of the end resonator, derived from graphs.
The process is described in the RSGB Microwave Handbook, a 3 volume set.

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