1.3GHz filter design
Just working on field trials of DigiLite-ZL (http://www.idesignz.org/DigiLiteZL/DigiLiteZL.htm) and need a half reasonable filter between the survey antenna and a portable DVB-S RX.
Current thoughts are to hand build an interdigital design using strips of FR4 + copper, maybe 2mm wide as the resonators, grounded at one end and tuned using low value Johanson PTFE trimmers at the hot end. Resonators will be somewhat short than quarter-wavelength and will be glued to a ground plane.
50R feed point will be a few % from the cold end, and probably need 5 poles (?) to achieve > 40db rejection at +-100MHz.
This really seems like the sort of thing that should have been done before, and before I grapple with uWave office (or ask some kind soul to) I am hoping that someone may have pointers to prior art.
I looked at PCB hairpin filters, but performance and centre freq is dominated by variations in batch to batch FR4 laminate manufacture. I considered using Rogers laminate, but this is not readily available so I am planning to stick with FR4 for the moment.
Thoughts and pointers please.