Here is a used waveguide variable attenuator made for the Military by Polarad (IIRC), my estimation of the  range is 0->20 dB,  reasonably flat over the entire band, covers 26-40 GHz, and has a WR-28 style flanges, four hole, used, good condition. This came from a Microwave development company and was used in their cal lab. Very useful for the  new comm bands opened up in Ka band.  Handy for adjusting level so you dont blow out that power head! Have fun! 

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