Study towards cryogenic Phased Array Radar Systems A. Froehlich, M. Tiesing and N. Ben Bekhti, F. Koenig, S. Putselyk, L. Naumann, F. Rahlf Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR, Wachtberg, Germany PAF Workshop 2017, Sydney
Contents Motivation of the study RADAR fundamentals GESTRA-Project Possibilities to improve the SNR System analysis Project realization Challenges of the study Dewar-design Collaboration with MPIfR Further project steps Outlook
Motivation of the Study Sensitivity improvement of Phased Array Radar-Systems for Space Surveillance by using cryogenic techniques Goal: Signal-to-Noise-Ratio (SNR) improvement using cryogenic-cooling of critical components and herby reduction of the system noise temperature
RADAR Fundamentals SNR = P Rx P N = P Tx G Tx G Rx λ 2 q 4π 3 r 4 Bk b Tn f Typical Radar Applications Classical Distance Determination ( ranging ) Speed Estimation by using Doppler Analysis SAR Synthetic Aperture Radar for RADAR imagining Two types of RADAR FMCW RADAR Pulse RADAR
GESTRA-Project In December 2014, the Federal Ministry for Economic Affairs and Energy (BMWi) of Germany assigned Fraunhofer FHR to develop and build a radar system for monitoring and tracking objects in low-earth orbit (LEO) The project is managed by DLR Space Administration and will be completed in 2018 Partly mobile experimental radar Installation on a site owned by MOD Remotely operated from the German Space Situational Awareness Centre
GESTRA-Project - System performance System performance Quasi-monostatic L-band radar System noise figure < 1.5 db incl. ADC 256 RX and TX elements 6.5 beam width at upper frequency +-45 E-plane and +- 60 H-plane scan area Directivity of 30.9 db 300 km 4400 km instrumented range Electronical and mechanical tracking mode
Possibilities to improve the SNR SNR = P Rx P N = P Tx G Tx G Rx λ 2 q 4π 3 r 4 B k b Tn f Increasing the number of receiver/transceiver modules Improved sensibility by using a cryogenic receiver system Increased receiver power consumption
System analysis LNA Digital Receive Module Antenna Antenna Losses Loss: 0.1 db LNA Gain: 20 db Feed Line Loss: 0.5 db DRM System temperature of the receiver: T sys = T receiver + T source + T Ground + T sky
System analysis Parameter 290K 77K (N) 20K (He) SYSTEM NOISE TEMPERATURE: Ohmical antenna losses [db] 0,1 0,1 0,1 Physical antenna temp. [K] 290 290 290 Physical ground temp. [K] 290 290 290 Integrated antenna sidelobe pattern towards ground (focussed to zenith) 0,18 0,18 0,18 Atmospheric loss (1-way) [db] 0,115 0,115 0,115 Effective noise temperature of atmosphere [K] 7,6 7,6 7,6 Effective noise temperature of space [K] 8,2 8,2 8,2 Efektive noise temperature of sun [K] 6,5 6,5 6,5 Effective noise temperature of sky [K] 21,92 21,92 21,92 ACTIVE ANTENNA NOISE TEMPERATURE (COOLED) [K] 75,17 75,17 75,17 Physical temp. of receive line [K] 290 290 290 Feed line loss [db] 0,1 0,1 0,1 RECEIVING LINE TEMPERATURE [K] 6,75 6,75 6,75 Receiver reference temp. [K] 290 77 20 Noise figure of receiver chain (inkl. ADC) [db] 1,1 1,1 1,1 RECEIVER TEMPERATURE 83,59 22,20 5,76 SYSTEM NOISE TEMPERATURE [K] 194,15 104,13 87,69
System analysis Parameter 20K 290K # TX elements 1 1 # RX elemente 7 7 TX element distance [Lambda] 0,55 0,55 RX element distance [Lambda] 0,55 0,55 Gain TX element[db] 6,8 6,8 Gain RX element [db] 6,8 6,8 G TX array (Beam broadening) [db] 3,8 3,8 G RX array [db] 15,3 15,3 Ptx element [W] 1 1 P tx array [W] 1 1 Frequency [GHz] 1,40 1,40E Number of pulses 1 1 PRF [Hz] 30 30 rcs [m²] 10 10 Distance [m] 500 500 SNR [db] 27,22 24,59 T Ground SNR improved by 2,6 db
Project realization To reach this effort this study includes Building up a lab for cryogenic measurements Design of a dewar Material characterization RF window materials Substrate materials Measurements of cryogenic LNAs Noise temperature characterization S-Parameter Limiter behavior study
Project realization Dewar design Multi-Stage cooling process Stainless steel housing Aluminum 4 K area Copper structures for thermal coupling Access point for a cooling head GM Sumitomo RDK-415D cooling head 2 nd Stage 1.5 W 1 st Stage 35 W 70 K Thermal Radiation Shield 4 K Thermal Radiation Shield 4 K Experimental Platform Thermal Coupling Sumitomo Cold-Head Interfaces
Project realization LNA noise measurement at MPIfR Building up a measurement station at MPIfR Becoming familiar with cryogenic techniques Study different noise temperature measurement possibilities Measuring noise temperatures by using a heated load (design by MPIfR) Used LNA types from S. Weinreb CITLF2 (SiGe) CIT118 (GaAs)
Project realization LNA noise measurement Further steps Set up and valuate measurement station at FHR Evaluate performance with MPIfR measurements Analyze the sensitivity of the measurement equipment Matching of non-cryogenic LNAs/transistors
Project realization Heated Load RF performance Standard FR4 PCB 50 Ohm RF matching 1 2 GHz @ < 10 db S11 Temperature control loop Heater power 5 W TVO temperature sensor range 1.5 375 K Cernox temperature sensor range 100 mk to 420 K
Project realization Single channel Mechanical structure requirements Using GFK for sturdy and lightweight structures Thermal coupled to 4K via copper bends Scalable for an antenna array Temperature sensors
Project realization Further experiments Possible antenna types Cavity-Backed Patch antenna Bow Tie antenna Antenna/array requirements Frequency range 1 to 2 GHz Dual-linear polarized Low cross polarization low mechanical extraction.
Project realization Further experiments Characterizing materials Ring resonator Filled waveguide Testing technologies of electronic components Study behavior of limiter structures PIN diodes Turn on time.
Conclusion This study is a first step towards sensitivity improved Phased Array Radar systems using cryogenic cooling Design of a Dewar Installation of a measurement station Identifying appropriate antenna and LNAs Studying measurements techniques in a cryogenic environment
Outlook Intelligent design of a 7-element array Design of an optimized vacuum vessel Scalable design for future use Weight optimization Future application for large GESTRA-like Phased-Array Radars for Space Surveillance
Thank you for Attention Questions? Marco.Tiesing@fhr.Fraunhofer.de Andreas.Froehlich@fhr.Fraunhofer.de