A waveguide-coupled thermally isolated radiometric source.

Area of Science:

• Physics
• Electrical Engineering
• Cryogenics

Background:

• Millimeter and sub-millimeter wave sensors require precise thermal sources for calibration and operation.
• Existing thermal sources often face challenges with thermal isolation and achieving high emissivity in cryogenic environments.
• Dual polarization capabilities are essential for advanced sensor applications.

Purpose of the Study:

• To design and validate a dual polarization thermal source for waveguide-coupled cryogenic sensors.
• To achieve high emissivity and effective thermal isolation for the source.
• To enable the source to operate at temperatures significantly higher than the sensor.

Main Methods:

• A waveguide-mounted absorbing conical dielectric taper was employed as the thermal source.
• A kinematic suspension using low thermal conductivity Kevlar threads was utilized for thermal isolation.
• The design allowed the waveguide to be heat sunk to the cryogenic system's lowest bath temperature.

Main Results:

• A 33-50 GHz blackbody source demonstrated an emissivity of 0.999 across the full waveguide band.
• The dominant deviation from unity emissivity was attributed to waveguide ohmic loss.
• A thermal time constant of 40 s was observed at an absorber temperature of 15 K.

Conclusions:

• The developed dual polarization source provides high emissivity and effective thermal isolation in cryogenic systems.
• The kinematic suspension ensures mechanical repeatability and reliability during thermal cycling.
• The source design enables precise thermal emission control for millimeter and sub-millimeter wave sensors.