Multi-layer low temperature superconducting K-band filter and diplexer design

A multi-layer Low temperature superconducting (LTS) Microstrip K-band diplexer is designed, fabricated, measured and reported for the first time. The Chebyshev K-band filters used in the device have five poles and are designed for the center frequencies of 20.45 GHz and 21.15 GHz with a bandwidth of 500 MHz. The dimension of the fabricated diplexer including the input and output Coplanar Waveguide (CPW) to microstrip transitions is only 3.2 mm × 2.2 mm. The diplexer is measured in an RF cryogenic probe station at 4K. A novel frequency independent broadband 50 Ω load is designed with the same fabrication process and used to match one of the three ports when the other two ports are being measured. Simulation and measured results of the diplexer show a spurious-free response up to 40GHz.