A Single-Block TRL Test Fixture for the Cryogenic Characterization of Planar Microwave Components

Abstract

The High-Temperature-Superconductivity (HTS) group of the RF Technology Branch, Space Electronics Division, is actively involved in the fabrication and cryogenic characterization of planar microwave components for space applications. This process requires fast, reliable, and accurate measurement techniques not readily available. A new calibration standard/test fixture that enhances the integrity and reliability of the component characterization process has been developed. The fixture consists of 50 Q thru, reflect, delay, and device under test gold lines etched onto a 254 urn (0.010″) thick alumina substrate. The Thru-Reflect-Line (TRL) fixture was tested at room temperature using a 30 Ω, 7.62 mm (300 mil) long, gold line as a known standard. Good agreement between the experimental data and the data modelled using Sonnet’s em © software was obtained for both the return (S11) and insertion (S21) losses. A gold two-pole bandpass filter with a 7.3 GHz center frequency was used as our device under test (DUT), and the results compared with those obtained using a Short-Open-Load-Thru (SOLT) calibration technique. Minimum insertion losses of 3.85 dB and 5.41 dB were measured with the TRL and SOLT calibration techniques, respectively. Room temperature return losses of 25.56 dB and 16.86 dB were measured using the TRL and SOLT calibration techniques, respectively. When used to perform calibrations and testing at cryogenic temperatures, the TRL fixture exhibited insertion and return loss data superior to its SOLT counterpart. A detailed description of the cryogenic components of the TRL fixture as well as results of their cryogenic characterization are presented.