Circuit Analysis for Stripline and Microstrip

Here was a question about the design of strip lines and micro strips:

At 10:16 PM 10/10/2007, Loren Moline WA7SKT wrote:

Does anyone know what the impedance of the 1/2 wave legs of a microstrip bandpass filter.

That is the ones you see with 3 poles and a 50 ohm line thru them from input to output tapped maybe 25% from one end?

The 1/2 wave lines are tied to ground at both ends. Thanks!

Loren

On Wed, 10 Oct 2007, Paul Wade W1GHZ wrote:

hi Loren,

I'd recommend you download a copy of Ansoft Designer SV (free Student Version) from www.ansoft.com and play with the filter wizard. you can play with all the parameters of different filters and get a feel for what might actually work.

results come out pretty close - you have to account for all the actual parasitics to get things right, or just attack it with an X-Acto knife for final tuning

73

paul

That's an excellent suggestion for anyone who doesn't yet have it. Ansoft Designer SV is one of the best free tools you're going to find.

Another is Sonnet Lite. Another freebie for use in microstrip design. I've used it in design and modification of hairpin filters, the stub filters Loren is describing, Lange couplers, etc. It's amazingly accurate in its response if you put the right parameters in. I recently used it to build some 1500 MHz hairpin filters for an LO that will be 32X multiplied as an LO for 24 and 47 GHz transverters.

Sonnet requires you to register the software on your computer before you can use the 16 Mb of RAM the Lite version needs. I think it will run with 1 Mb without registering, which really isn't enough to use for most filters. They usually will send you an information package once after you register and maybe an e-mail and after that they don't hassle you. As far as I know they do NOT give away your e-mail address or other info, for those who are squeamish about such things.

Another once-available cheap software program was PUFF. I think I paid $10 for it when Cal Tech was selling it. Now I believe ti's only available by buying someone's book for $60 (it comes with the book). Or if you can find another source for it. It's a DOS-based program and is very small yet powerful. And it's FAST. I will run a design on both PUFF and Ansoft Designer and the two have always agreed in results. I still use PUFF quite a bit.

73, Zack W9SZ

PUFF is GPL and available http://wwwhome.cs.utwente.nl/~ptdeboer/ham/puff/

Since many people dont have the $ or the acess to good tools at work i have taken the time to put together some recomendations for free or low cost tools to make life easier ! be aware that most tools listed are for non commercial use only !

1. Ansoft Designer SV: Good subset of a commercial high $ package, covers layout and EM Simulation (planar EM ), what im missing is a optimizer function but has tune function to make up for it, good model database, lots of models and substrates ! FREE
2. EM3DS 2.5D: EM Simulator, italian company has a freeware version for download thats limited in size but still usefull.
3. WIPL-D: 3D EM Simulator, freeware version, full version reasonably priced !
4. Sonnet Lite: One of the best known names in EM Simulation, very easy to use tool, several levels of licensing from free version over a $499 version to $$$$$, good tool !
5. Genesis (Eagleware elanix): Good starter tool , low cost , worth the money for possible trade up against MWO !
6. Quartus Webpack: FPGA Design tools, altera lately added almost all megafunctions and devices except of a few very high end Stratix devices to the webpack ! FREE Software
7. XILINX Webpack: Free

A few words to Microwave CAE, every program is only as good as its models and the circuit description you provide ! if you design an amplifier and dont add your ground vias for the source terminals to your netlist you will never see the light ! linear simulators also never account for lids and housings effects like those are best simulated with a EM Simulator tool ! Last but not least you get what you pay for however the advantages of a high $ product will not show in the low frequency regions, if you design 3 or 6GHz stuff Genesis will do you as well as ADS or MWO if you get higher you will quickly feel the pain ! having driven almost anything from Eagleware over ADS to MWO i can speak out of experience.

Lothar