Impedance Matched Absorptive Thermal Blocking Filters
  We have designed, fabricated and characterized absorptive thermal blocking filters for cryogenic microwave applications. The transmission line filter's input characteristic impedance is designed to match $50\,\Omega$ and its response has been validated from 0-to-50\,GHz. The observed return loss in the 0-to-20\,GHz design band is greater than $20\,$dB and shows graceful degradation with frequency. Design considerations and equations are provided that enable this approach to be scaled and modified for use in other applications. 
E.J. Wollack, D.T. Chuss, K. Rostem, and K. U-Yen
astro-ph.IM physics.ins-det physics.optics