Feeling Out Filter Options

I was reading your article “Searching through Software for a Filter” (March 2012). You’ve covered lots of useful software I didn’t even know about that captures both synthesis and realization of different filters. However, there are also pure synthesizers out there that are equally important, especially for coupled filters (pretty much all narrowband  bandpass/bandstop filters). There’s the CMS tool from Guided Wave Technology (www.guidedwavetech.com) and a similar tool from CoupleFil (www.couplefil.com), both about $1000 for a license. I’ve also just started developing a synthesizer for iPhone/iPad called Couplings Designer, which is a $30 download from the Apple iPhone AppStore (www.applied.com/iphone) or free for the lite version.

These synthesizers are not capable of realizing a filter in terms of physical dimensions, but the couplings can be easily found from tools like Momentum from Agilent Technologies and  HFSS from Ansoft (www.ansys.com),  Microwave Wizard from Mician (www.mician.com) is another great tool you didn’t write about that can be used to fully design filters and uses mode-matching, which is incredible fast compared to method-of-moments (MoM) or finite-element-method (FEM) approaches (but quite expensive).

I hope these tips can be useful in future articles on filter design. Many think it’s some kind of black art. But as you pointed out, there are lots of tools available—many even for free—to the engineer that can be helpful to understand and demystify filter design.

Göran Granström

Software Supplements

I was enjoying my May issue and the article “Matching Software to Design Needs.” I noticed you hadn’t mentioned the program BAMP that was an early S-Parameter CAD tool in the ’70s, that ran on HP Basic controllers/desktop calculators from Hewlett-Packard Co. (www.hp.com). Also, there is a GPL-license freeware simulation tool called QUCs (Quite Universal Circuit Simulator; http://qucs.sourceforge.net). It doesn’t have all the tools and bells and whistles that are available in the commercial programs, but it’s not bad!

Bill Clausen
Prowave LLC

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