Low-Loss Millimeter-Wave Isolators for Cryogenic Systems

The primary objective of the proposed SBIR Phase II research is to extend the room temperature millimeter-wave (MMW) technology developed by Micro Harmonics to isolators operating at cryogenic temperatures. Two very successful cryogenic prototype devices at WR-10 (75-110 GHz) were designed in the Phase I effort. The measured insertion loss at 77 K is 0.3 dB and the isolation is greater than 25nbsp;dB across the band. In the Phase II program we propose to develop a line of cryogenic isolators optimized for cryogenic temperatures operating in every waveguide band from WR-15 through WR-5.1 and to deliver prototype devices at each band to NASA. We will also design cryogenic isolators for the WR-4.3 and WR-3.4 bands. These components will fill an unmet need and find immediate application in many cryogenic systems now being developed for NASA missions.Cryogenic cycling puts mechanical stresses on the constituent parts of the isolators that can ultimately lead to premature failure. Part of the proposed research is to identify and mitigate potential failure mechanisms so that the isolators can reliably withstand multiple cryogenic cycles over the lifetime of the device. This task is accomplished through sophisticated thermal stress modeling as well as repeated cryogenic cycling of the isolator assemblies.A WR-2.8 (260-400 GHz) isolator designed in the Phase I will be assembled and tested. This isolator will be the first of its kind at this frequency. A novel line of MMW voltage variable attenuators (VVA) will also be developed. The VVArsquo;s utilize the Faraday rotation effect in a similar way as the isolators, but with a variable magnetic bias field instead of a fixed saturated magnetic field. Initial investigations indicate that the effective attenuation range should be at least 1-35 dB in the WR-10 band. NASA researchers at JPL have expressed their interest in these devices.