Hello Andy,

Reading some comments of yours on one of my currently infrequent visits to ukmicrowaves,

I gather that you are looking at printed microwave filter designs. I suggest that you _don't_ look at microstrip. Over the last few years a whole new family of filter designs have begun to emerge using TMxx mode cavities etched onto (or into) PCBs. These are called 'substrate integrated waveguide' (SIW) filters I've played with this approach, and it works. There is one particularly attractive family of these filters called 'empty SIW' filters which eliminate dielectric losses pretty well completely, so very low-loss filters (and matching networks) on PCBs are entirely practicable.

I played with the technique just before I left Wales, and made a little 2-pole 10GHz filter on FR4 using a pair of semi-circular cavities. Even on FR4(!) the insertion loss was acceptable for many non-critical applications and the filter didn't take-up a lot of space. I haven't had a chance to carry that work forward yet, so I thought I share the idea with you.

A literature/inet search should prove fruitful. For historical reasons I am a member of the IEEE Microwave Theory and Techniques society, and their monthly magazine has had a number of articles on the subject. I'd keep my membership of MTT-S even if I had to let the RSGB go hang!

Hope that's useful.

Chris 'dgu






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Chris Bartram G4DGU