W(width) L(length) S(spacing) Coupled-Line Band-Pass Filter

Hi all..I am working on a "Coupled-Line Band-Pass Filter Design" I need actual equations for W(width) L(length) S(spacing) , I know they can be calculated by using Linecalc function of ADS but I need the eqns so I can demonstrate in presentation how the W,L,S is calculated .Plz help me ...I'll b waiting for replies .
Thanks.

This is complex problem,
irst you need to freeze the specification, find the approach filter type and then order, then target for WLS for each finger.

There are equations available for coupled microstrip lines but they are either inaccurate or ultra complex! see for example:

[/url] http://qucs.sourceforge.net/tech/node77.html[/url]

You might want to ask yourself why you need them for printed filter design. The lines in a printed filter can be all the same width. The lengths of the lines set the resonant frequencies and the spacing sets the coupling coefficients.

See http:www.rfshop.co.uk/PrintedFilters.doc

I m looking for Microstrip line....

Added after 5 minutes:

Thanx peter Martin

The paper:

"Hairpin-Line and Hybrid Hairpin-Line/Half-Wave Parallel-Coupled-Line Filters" by Cristal, E.G. Frankel, S. Microwave Theory and Techniques, IEEE Transactions on
Publication Date: Nov 1972, Volume: 20 Issue: 11, page(s): 719 - 728

is a good starting point and has, I think, the design equations that you are asking for.

Dishal in the 60's wrote that mechanical filters didn't have to have resonators of different impedances, as the designs of the time implied. This made the process of filter design much simpler and his point is just as true with printed filters too.

see M Dishal “A simple design procedure for small percentage bandwidth round rod interdigital filters,” IEEE Trans. Microwave Theory Tech., Vol. 13, No. 5, 696–698, Sept. 1965.