The presentation will present a brief description of the principle of very-low-noise technologies, the reliability problems that have to be solved in order to ensure maximum availability of the cryogenic receiver system in an operational environment, the new generation of cryogenic receivers, which will be deployed in DSA3 antennas and new concepts of miniaturized cryogenic low-noise amplifiers, which can be used in small antennas for very-high-data-rate applications.
Text of OPS Forum Cryo Systems ESTRACK 16.10.2000
1. Cryogenic Receivers: Closer to the noise floor Present and future ofCryogenic Receivers in ESTRACK
2. About Myself
Ground Station engineering division / RF and signal processing section.
Cryogenic receivers/ amplifiers
Frequency converters (Ka band deep space up/down converters)
Studies with European universities
SSA radar development
What is a Receiver?
an electronic device that changes a radio signal from a transmitter into useful information
What does Cryogenics deal with?
The wordcryogenicscomesfrom Greek and means "the production of freezing cold.It is commonly admitted that the field of Cryogenics covers range of temperature below -180 C (Nitrogen boiling temperature).
Why cryogenic receiver?
Because during propagation a radio signal is affected by external perturbation. In particular noise created by cosmic radiation and thermal noise due to the particles random movement.Cooling down the devices reduces this noise drastically.
5. Deep space telemetry P transmit= 28 W Ant diameter = 2.2 m Distance= 500 million km
Antdiameter = 35 m
P receive= 1x10 - 16Watt (0.0000000000000001 W) 6. Noise in space communication Total sky noise and antenna noise power= 1 x 10-17W (16 zero after the point) 7. Noise in electronic equipment Standard amplifier: Receiver Noise = 2x10 -15W 8. Signal over Noise Ratio
Signal 1x10 -16W
Antenna + Atmosphere Noise 1x10 -17W
Receiver Noise 1x10 -17W
Signal/Noise 5 (7dB)
9. Very low noise amplifiers
The noise power generated by a standard amplifier and receiver thermal noise is higher than the signal power to recover
Need to develop very low noise amplifier using:
Very low noise transistor technology
Cool down the receiver in order to decrease the thermal noise
Deep Space antenna uses High Electron Mobility Transistors cooled down at 15K in order to be able to retrieve deep space signal from the noise
10. High Electron Mobility Transistors 11. InP Technology 12. InP Technology
GaAs (gallium arsenide ) transistors are widely use in the Telecom industry and can be provided easily by standard manufacturers (Mitsubishi)
InP technology is not available from standard manufacturer and was only available in USA but protected by ITAR regulation.
It has been necessary to develop InP devices in X and Ka band with European universities in order to minimize the receiver noise.
13. InP Transistors 14. X band Low Noise Amplifier 15. Ka bandlow noise amplifier 16. Cryogenic cycle
Heat removed from outside
Heat transferred outside
17. Vacuum Dewar: Heat transport mechanism Convection Conduction IR Radiation Gas molecule Vacuum Enclosure Cooled Sample , cryogenic temperature Sample support structure Dewar wall Convection, conduction, radiation How to reduce these thermalloads ? Convection : remove physical support = air molecules = processvacuum(pressure