In order to detect debris in near-earth orbit, monitoring using radar technology is becoming increasingly important.
The use of cryogenic technology is intended to increase the sensitivity of future phased array radars in order to enable the detection of even smaller parts.
For this purpose, the system noise temperature of receivers will be considerably reduced by a technical realization of efficient cooling measures.
State of the art:
- In radio astronomy, receiver cooling for parabolic mirror feeds has been established for decades.
- For phased array systems, development is still in its infancy due to the mechanical and high-frequency challenges involved.
- The main part of the system noise in a receiver chain is generated by the first amplifier (Low Noise Amplifier, LNA).
Challenges:
- Cooling of the first amplifier stage with gaseous helium to below 20 K (-253°C) to reach system temperatures below 50 K -> Improvement of SNR by ~3 dB, which means that objects with half the radar backscatter cross section can be detected in orbit
- Development of an experimental system (measuring dewar, H: 840 mm, diameter 620 mm) that can reach a temperature of 4 K (-269 °C) on the experimental platform.
- Creation of a suitable infrastructure for the safe handling of inert gases (helium, nitrogen) and liquid nitrogen.
- Development of an optimized temperature control and monitoring system
- Realisation of a high vacuum to reach lowest temperatures
First draft of an "RF-Unit" and the characterization of cryo-suitable LNAs at 4 K
- The "RF Unit" serves as carrier construction for the high-frequency amplifiers to be cooled.
- Scalable design, so that it can be used for a phased array system
- Thermal insulation between 1st and 2nd stage of the cryocooler
- Connection of low noise amplifiers to the 2nd stage of the cryo cooler
- First results: LNAs achieve a noise temperature of ~ 6 - 8 K at 1 to 2 GHz and an ambient temperature of 12 K with the current measurement setup.
Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR
