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OPS Forum Cryo Systems ESTRACK 16.10.2000
 

OPS Forum Cryo Systems ESTRACK 16.10.2000

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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 ...

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.

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  • Few definitions Receiver is an electronic device which converts a radio signal that can be propagated in free space into a useful information which can be the sound of a radio or data which can be interpreted by a computer. Cryogenics comes from the Greek usually it is considered that the field of the Cryogenics science covers temperature below -180 C. Why do we want to cool down a receiver? Actually we will see that the received signal is mixed with noise (This noise is seen as on the TV specially the old analogue TV if your antenna is not well tuned). This noise still exists in digital TV but correction algorithm are implemented in order to reduce the effect. We will see that cooling down the receiver devices reduces the receiver thermal noise and helps greatly to recover the wanted signal.
  • What’s the power of a signal coming from a spacecraft located at 500 millions km. If we consider that a spacecraft such as Rosetta transmits 28W (equivalent to a small light. Antenna diameter of 2.2m in order to focus the radio signal in the direction of the earth. 35m Antenna on the earth
  • As we mentioned in the introduction, the signal coming from the spacecraft is affected by difference source of noise. Clouds/ rain Atmosphere propagation Cosmic noise (Galaxies and background noise) Sun Noise The average power of the noise (Excluding rain noise) is about 10 power -17. Which is still 10 times lower than the power of the signal
  • The very weak signal has to be amplified by the receiver if we want to exploit it. Unfortunately during the amplification and transmission noise is added to the signal. This noise is due mainly to the thermal agitation of the electrons which is superimposed to the signal. Considering a standard amplifier from the shelves the noise power which is added to the signal is 2x10-15 W. 20 times more powerful than the signal! It s not possible to recover the signal
  • If we want significant margin to be able to recover the signal we can specify than the received signal shall be at least 5 times higher than the noise. Then the receiver noise must be at maximum 10 -17W! 200 times lower than a standard amplifier! In order to achieve such a performance, it is necessary to develop a new technology.
  • In order to meet the noise requirements it is necessary to develop new technology: Developing very low noise transistor technology and to cool down the receiver at cryogenic temperature to decrease the thermal noise at the minimum..
  • In the first picture is presented the principle of a field effect transistor. The current flow is modulated by the voltage applied to the gate. A very small voltage variation on the gate can produce a large current variation in the Channel. The ratio between the current variation and the gate voltage variation is called transconductance. The current in channel is also modulated by the thermal noise (random movement of the electron which is superimposed to the electron flow. In order to minimize the noise it has been developed in the 90 s a high electron mobility transistor. The principle is the same of a standard field effect transistor but with an HEMt the electron flow movement is constraint in a very thin layer (2D electron gaz) which limit the thermal agitation.
  • The mobility of the electron in a HEMT depends as well on the substrat. In this graph we can see the frequency range for certain substrate are higher which mean than the mobility of electrons is higher in this substrate. The highest is the mobility as well the lower is the noise because the flow of electron is less perturbed by the crystal of the substrate.
  • GaAs devices are comonely used on the market however InP are only available in the USA for “military”uses.
  • Here is a picture of the InP transistors with the universty of zurich, The transistor is composed of 2 gates. The gate length is about 0.2 um. Usually the lower is the get length and the higher can be the frequency range and the lower is the noise.
  • The transistor itself is inserted in a box with additional components in order to bring the DC current to the source and drain. The transistor is mounted on the dielectric substrate by meam of wire bondings.
  • This is an example of another amplifier working in Ka band. In this circuit a single transistor is used in the fist stage. And the following stages are made by Monolithic Integrated Circuit which is a full circuit is etched inside the substrate.
  • This animation shows the principle of a closed cycle refrigerator which is used for the cryocooler. During the first phase the gaz inside the piston is exposed to the oustside and the heat accumulated during the gas compression is evacuated. The surface in contact with the gaz is becoming hot. During the expansion phase, the the piston is isolated and no heat is exchanged with the outside. So the expended gas is cooled down. During the next compression phase the gas is exposed to the outside and extract the heat of the surface in contact. The surfaced is cooled down. From one cycle to the other, the surface in contact with Tc is cooled down furthermore until it reaches an equilibrium.
  • In order to be able to cool down the device at cryogenic temperature, the thernal load from outside must be reduced to the maximum. Outside thermal load are Convection (macroscopic movement of the air) , Conduction (Heat transfer via mollecule movement) and Radiation (Heat transfert by mean of electomagnetic waves, mainly infrared)
  • The signal coming from the antenna feed go through a polarizer in order to separate the 2 polarizations and goes to the cryogenic receiver. The cryogenic receivers is made of filters and low noise amplifier. Only the first amplifier is cooled down because it is the major contributor of the noise. The noise of the following devices is reduced by the first amplifier gain and is negligeable.
  • This is a closer view of the Cryo LNA subsystem including compressor , external power supply and the monitoring feature connected to the LAN network.
  • The cryogenic receivers includes input WG with a special material (Invar) which is a good electrical conductor but bad thermal conductor. The WG is followed by a cryogenic filter, and then the HEMT amplifier. The Cold head cooled at 15K is shown as well.
  • This is the measured performance of the Cryo receiver, the measured equivalent noise temperature is 11K. (This is equivalent to the noise generated by a resistor cooled down at 11K The measured gain is closed to 60 dB which means that signal is amplified by 1 million.
  • The S band dewar is larger because at lower frequency, the waveguide is much bigger, as shown on this picture.
  • This is working in Ka and it has the particularity to cool down the feed the polarizer and filters.
  • The LNAs are located in the Antenna equiment room of the antenna. Th S band LNAs are located in the basement.
  • This chart shows the number of failure we had since DSA1 is in operation in 2001. The normal servicing interval is 10000 h but what we see is that a lot of failures appears before 10 000h. After few years of operation the experience shows that the reliability of the cooler must be improved in order to have an optimum availability of the subsystem.
  • For the maintenance or repair of the system we have to wait 12hours before the system is warm, then we have to wait 7 hours for the cool down to 15K. The manufacturer recommended to perform 2 warmup cool down brfore declaring the system operation. This means that the cryo receiver is unavailable for 41 hours.
  • How to make the system more reliable and improve maintainability? Major source of problem is high vacuum because there are always micro leakages and it is necessary to evacuate the dewar regularly. What s more if there is a power failure the gas condensated on the cold head outgases and the system cannot restart automatically. The uses of new solid insulator allow the system to work at atmospheric pressure. In order to improve the reliability, we are going to change the cooler with a Summitomo cooler which is used by 90 % of the MRI machine. This is a guarantee of reliability and we know that the provider has the critical mass tu ensure the durability of the coolers - To improve the maintainabilité we are going to implement heaters for fast warmup and we are going to use a cold head sleeve in order to speed up the cold head exchange in case of failure.
  • This is a sketch of the sleeve concept. The cold head is clamped to the sleeve a cryogenic temperature by mean of a clamp system using materials with different expension coefficient. Whe the system warms up the clamp expands and the cold head is released.
  • The aerogel material is made of micro balls, in this microballs it exists an extremely large number of cavities which ensure the thermal insulation. The aerogel is treated with titanium which is a very good shield against radiations. This material is used for the insulation of the spce shuttle cryogenic tanks, it is used as well to insulate pipe lines located on the bottom of the oceans.
  • The second generation of cryo receiver will implement these technology
  • Thermal simulation has been made on the second generation dewar in order to validate the design. It is shown than with an external temperature of 300k, the LNA and the cryogenic filters will still stay at 15K.
  • This picture shows another concept of LNA this cryogenic LNA is much more compact and can be installed very close to the feed of the antenna. The devices are cooled down at 60k instead of 15K and the noise performance are slighly degraded compared to the 15K LNA
  • This compact LNA has been installed in Kourou feed for the support of deep space mission. It has been working for 3 years now without any major failure.
  • Another concept still under development is the miniaturized cryogenic LNA using a miniaturized coolere.
  • The cooler has a limited power and only cools down the MMIC attached to it.
  • MMIC integrates not only the transistors but all the componants of the complete amplifier.
  • This pictures shows a prototype of the miniaturized LNA. The mini LNA is not bigger than one and.
  • Future missions such as Mars robotic exploration and later on human exploration will require a large amount of data. To achieve a large datarate the signal over noise shall be quite large as well. We see on this graph than with a current 35m antenna, in Ka band, we are limited to 1Mbits/s (Even much less in X band). The only way to increase the datarate is to build a network of antennas.
  • JPL concept is a cluster of 12 m antennas which will be managed by a sigle Array control center.
  • Each antenna includes a cryogenic receiver in order not only to improve the gain the the noise as well
  • The cryogenic receiver in deep space array is a dual band receiver, the feed is able to select X and Ka band and all the receiver is cooled down including feed and polarizer.

OPS Forum Cryo Systems ESTRACK 16.10.2000 OPS Forum Cryo Systems ESTRACK 16.10.2000 Presentation Transcript

  • Cryogenic Receivers: Closer to the noise floor Present and future of Cryogenic Receivers in ESTRACK
  • About Myself
    • Ground Station engineering division / RF and signal processing section.
      • Cryogenic receivers/ amplifiers
      • Frequency converters (Ka band deep space up/down converters)
      • Radiometer.
      • Studies with European universities
      • DSA3
      • SSA radar development
  • Introduction
      • What is a Receiver?
        • an electronic device that changes a radio signal from a transmitter into useful information
      • What does Cryogenics deal with?
        • The word cryogenics comesfrom 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.
  • Introduction
    • How a deep space telemetry signal is propagated.
    • Very Low noise Technology.
    • Cryogenic technology
    • Deep space cryogenic receivers and improvements
    • Compact, miniaturized cryogenics Low Noise Amplifiers
    • Future developments
  • Deep space telemetry P transmit= 28 W Ant diameter = 2.2 m Distance= 500 million km
      • Ant diameter = 35 m
    P receive= 1x10 - 16 Watt (0.0000000000000001 W)
  • Noise in space communication Total sky noise and antenna noise power= 1 x 10 -17 W (16 zero after the point)
  • Noise in electronic equipment Standard amplifier: Receiver Noise = 2x10 -15 W
  • Signal over Noise Ratio
    • Signal 1x10 -16 W
    • Antenna + Atmosphere Noise 1x10 -17 W
    • Receiver Noise 1x10 -17 W
    • ----------------------------------------
    • Signal/Noise 5 (7dB)
  • 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
  • High Electron Mobility Transistors
  • InP Technology
  • 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.
  • InP Transistors
  • X band Low Noise Amplifier
  • Ka band low noise amplifier
  • Cryogenic cycle
      • Heat removed from outside
      • Heat transferred outside
      • PV=cstxT
  • 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 thermal loads ? Convection : remove physical support = air molecules = process vacuum (pressure <10-3 mbar) inside the Dewar. Conduction : Remove physical support when possible (i.e. process vacuum ); select material with low thermal conductivity at operational temperature. Radiation : Use Infra-Red reflective materials such as MLI (Multi-Layer Insulations) to stop radiations. Select material with low emissivity factors to reduce absorption of IR at operational temperature.
  • Cryogenic Receiver in Deep Space Antennas
      • - 2 S- Band in New Norcia
      • 4 X- Band in New Norcia and Cebreros
      • 2 Ka Band in Cebreros
  • Cryogenic Receiver
  • Cryogenic receiver
  • Gain and noise performance (room/ cryo)
      • Equivalent Noise Temperature: 11K
      • Pnoise=1.2 x10 -17 W
      • Gain=57 dB
      • Signal is amplified 1 000 000 times
  • S Band Cryogenic Receiver
  • Ka Band multichannel Receivers
  • In the Antenna Equipment Room
  • Reliability
  • Maintainability
    • Time to cool down = 7 hours
    • Time to warmup = 12 hours
    • Time for repair= 3 hours
    • Test = 2 Warmup / cool down cycle to declare the system operational
    • The system is unavailable for 41 hours minimum during servicing/repair
  • Reliability and maintainability improvement
    • High vacuum is difficult to maintain and needs regular pumping
      • Replace vacuum insulation with new generation solid insulator (aerogel)
    • The cryocooler is not reliable as a lot of failures occurs before the recommended maintenance period
      • Change cryocooler with a more reliable solution: Summitomo cryocooler is used in 90% of medical magnetic imaging machines
    • In case of failure the exchange or repair of the cooler has to be done by specially qualified staff and is very time consuming.
      • Implement a cold head sleeve for rapid exchange of the cooler
      • Implement heaters in order to reduce the warmup time to 2 hours
  • Cold head sleeve
  • Aerogel
      •  nanotechnology product = dried silica gel
      •  nullify three methods of heat transfer:
      • Convection : aerogel is a closed lattice and thus limits air convection
      • Radiation : aerogel selected is IR opacified to stop radiations
      • Conduction : . @ atmospheric pressure, aerogel is one of the most insulative material ever
  • Second generation
  • Thermal simulation
  • Kourou cryogenic LNA
  • Kourou cryogenic LNA Integration
  • Miniaturized cryogenic LNA
  • Miniaturized cryo LNA
  • Microwave Monolithic Integrated Circuit
  • Miniaturized cryogenic LNA
  • Data rate limitation
  • DSN array (JPL)
  • DSN Array (JPL)
  • X Ka band cryogenic receiver
      • Dual frequency feed
      • 31-38 GHz Ka LNAs
      • 8-8.8 GHz X LNAs
      • 15 K refrigerator
  • Conclusion
    • Next generation of cryogenic receiver will include all the passive elements in front of the Low Noise Amplifier to lower thermal noise.
    • New technology of low noise amplifier to be developed for high frequency (SiC, GaP)
    • Cryogenic receiver will be included in arrays antenna to increase the gain and reduce the noise simultaneously