filter

Here's the cool EMVU (Sonnet 5.1a) picture for my first "hairpin" filter.

Classic Microstrip/Stripline Filter Design Synthesis

(version 1.1 11/25/2001)

LLfilter.zip - this bundle includes a MathCad worksheet (and PDF format for viewing if you don't have MathCad) for synthesizing edge coupled bandpass filters (almost identical for the straight or hairpin shaped resonator cases) as well as stepped-impedance lowpass filters and lumped lowpass/highpass filters.

This is a more compact "hairpin" type as described by Kenichi Takahashi, Morikazu Sagawa, and Mitsuo Makimoto in "Miniaturized Hair-Pin resonator filters and their applications to receiver front-end Mics", 1989 MTT-S Digest. I've had fairly good luck designing these. though I haven't really used the design procedure in this paper, it is where I got the idea.

This picture was generated using Sonnet Lite plus (a tool that is well worth the price tag for small to medium sized EM problems (of course these terms are relative... I consider most of the EM analysis that I do on the "medium demanding" level at most). One feature that is added with the "plus" over the free version is the DXF import capability, so you can use something like Eagleware Genesys schematic/equations/Layout to generate "artwork". I do this constantly because it's very easy within Genesys to setup equations that can adjust an entire filter structure (such as those above) with just a few variables (this makes it easy to reuse designs and also really helps when you're trying to make sure that all dimensions map nicely to the EM grid).

Eagleware also offers some really nifty synthesis tools for lumped and distributed filters (FILTER, M/FILTER, and S/FILTER) as well as an integrated EM simulator (EMPOWER). If you're on a budget and need to do some microwave filter work, I highly recommend Eagleware Genesys (basic package includes linear simulator, layout, schematic entry) coupled with something like sonnet LitePlus. With that as a very solid starting point, you can gauge which direction you might want to go (synthesis tools, different EM simulation capabilities, etc).

I just received sonnet lite plus version 8 (6/19/2002) and found that I could do a nice analysis of this the "compact" filter above in perhaps 3 minutes (on my newer computer). The new ABS feature showed exact agreement (visual on graphs), yet smoother curves with 5 frequency points (analysis frequencies). Previously I used 41 points to achieve resolution that wasn't even as good, which took at least (41/5) times longer! The particular sweep range was roughly 2.5 times the passband width, centered on the passband response.

I think we should commend Sonnet and Eagleware for keeping the "starting price" of their tools affordable and the quality exceptional.