Phased Array Antenna Measurement in Near Field Range, Jorge Salazar

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Practical Consideration for Near-Field Phased-Array Antenna Measurements

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Phased Array Antenna Measurement in Near Field Range, Jorge Salazar

  1. 1. Practical considerations for a Near-Field antenna measurements MICROWAVE REMOTE SENSING LABORATORY SEMINAR UNIVERSITY OF MASSACHUSETTS, AMHERST Presented by: Jorge Luis Salazar-Cerreño R jlscerreno@gmail.comcasa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere March 28th, 2011
  2. 2. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Outline • Introduction of antenna pattern measurement I • Practical considerations for Near-Field antenna measurement – Alignment of AUT and probe – Span size and sampling spacing – Probe correction – Scattering multireflection in the room – Leakage – Error budget • CASA Phase-tilt antenna patterns • Recommendations for antenna test plan
  3. 3. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Outdoor antenna measurements • Outdoor Antenna Test Range (OATR) is used for moderate FF distances. • One critical factor in outdoor range systems is to find a place free of clutter and free of RF interferences. • Another critical factor is environmental changes (rain, humidity, temperature, etc) that can delay the test. • The scanners required are inexpensive in comparison with dB Systems Inc. the indoor range systems. The 2005 So. Turf Sod Rd. Hurricane, Utah 84737 U.S.A. equipment cost of the scanners can be lower than $40K.
  4. 4. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Example of FF antenna measurement 0 -5 -10 -15 pattern (dB) -20 -25 -30 Simulated FF-Measured -35 -40 -40 -35 -30 -25 theta(deg) X-Band Frequency Scan Array Antenna 64x64 Microstrip Patch Antenna Elements Eric Knap and Jorge Salazar
  5. 5. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Indoor FF measurements Advantages – Provide a controlled environment and an all-weather capability. Can eliminate delays due to weather (rain, humidity, temperature changes, etc) – The measuring system is time and cost effective. It requires only a small area. – Patterns are as accurate as those measured in a FF range – Can provide a full characterization of the antenna patterns. – Compatibility with security requirements Disadvantages: – FF distances FF=2D2/ Lambda – Cost is driven by the absorbers and scanner . pag#&#
  6. 6. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Limitations of indoor FF measurements 2 2L d FF  
  7. 7. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Measured Elevation Patterns in Indoor Far field rangeExample of the limitations FF INDOOR 1rst SLL higher inof indoor FF measurements 2-3 dB than expected Measured Elevation Patterns in Planar Near Field range PLANA NF • X- Band CASA array antenna • AUT size: 0.5mx0.25m • Frequency: 9.36 GHz • Far-field distance :16m • Length of range:7m
  8. 8. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere FF distance limitations in FF range systems (MIRSL antennas) S-band C-band X-Band Ku- Band Ku- Band Ka- Band W- Band CASA Units FM-CW IWRAP IWRAP AMFR AMFR AMFR X-POL Frequency GHz 2.94 5.11 9.36 13.25 13.25 33 95 Lambda m 0.1020 0.0587 0.0321 0.0226 0.0226 0.0091 0.0032 3dB BW deg 3.00 6.58 2.08 6.40 0.75 0.70 0.70 Aperture size m 2.21 0.58 1.00 0.23 1.80 0.91 0.35 FF Distance m 95.7 11.5 62.4 4.7 286.2 182.2 77.6 FM-CW: Frequency Modulated Boundary Layer Profiler 2 L2 2 L2 f   IWRAP: Imaging Wind and Rain Airborne Profiler CASA/X-POL: Ip1 ,Phase-Tilt and X-POL Radar Systems d FF AMFR: Advance Multi-Frequency Radar (AMFR)  c
  9. 9. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Compact antenna test range (CATR)• Compact Antenna Test Range (CATR) uses a reflector, or set of reflectors, designed to collimate the radiated pattern and create a plane wave at considerably shorter distances.• CATR provides a good protection against weather , RF interference and security.• CATR is costly (3X-4X FF indoor). – Requires a heavy 3 axes positioner – Requires larger space than FF Indoor X-band surface surveillance radar test in the compact – Requires expensive rolled-edge reflector antenna test range at the companys facility in Hengelo, to reduce diffraction and quiet-zone the Netherlands. (ex. $250K for only the reflector)
  10. 10. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Near-Field (NF) range system • NF provides the same advantages of any indoor range system in terms of controlled environment, real estate, interferences and accuracy. • NF provides additional features, such as back field projection, that are helpful to detect anomalies in the surface of the AUT, especially in active phased-array antennas. • The Near-field range consists of a interferometer connected to a field-probing antenna carrier by a precise robotic system. The antenna probe is moved through a planar, cylindrical or spherical surface near the antenna under test (AUT) • The near-field system operates by measuring the phase front of the AUT and mathematically transforms the phase front into the equivalent far-field angular spectrum. For a planar near field, the phase front and angular spectrum is related to the Fourier Fast Transform (FFT) pag#&#
  11. 11. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere What kind of scan surface NF use? CASCA antenna lab has a P-C and S Near-Field system pag#&#
  12. 12. casa Engineering Research Center for CollaborativeAdaptive Sensing of the Atmosphere Antenna range systems at UMASSCASCA antennas Lab. has two range systems. • NSI Taper FF range system – Frequency Range : 1-40 GHz, – Absorber size: 6” (CF-6, 32dB@3GHz-50dB @50GHz) – Length: 21’ (6.4m) – 1 axes-positioner – Base on PNA 8360 (1-40GHz) • NSI S-C and Planar NF range – Frequency Range : 1-40 GHz, – Absorber size: 8” (30dB @1GHz-50dB @50GHz) – Length: 14’x10’ (4.2mx3.0m) – 1 axes-positioner for S and C – Only in operates in CW mode – Base on PNA 8360 (1-40GHz) pag#&#
  13. 13. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Practical considerations to perform a NF antenna measurement • Alignment of the AUT and probe • Span size and sampling • Truncation effect • Scattering and reflections pag#&#
  14. 14. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Effects of misalignment between probe and AUT Beam Pointing Errors in P-NF (in deg) • Alignment is more critical Band S-band X-Band Ka- Band Aligment CASA , X- in NF spherical and NF Accuracy FM-CW POL AMFR cylindrical in NF scanners Frequency GHz 2.9 9.4 33.0 Lambda m 0.10 0.03 0.01 • In NF planar scanners the 3dB BW deg 3.00 2.08 0.70 alignment depends on the Antenna size Visual (1cm) m deg 2.21 0.130 1.00 1.146 0.91 6.274 AUT size and mechanical Tape measur. (5mm) deg 0.065 0.573 3.147 Laser (0.1mm) deg 0.001 0.011 0.063 stress pag#&#
  15. 15. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Effects of misalignment between probe and AUT (cont) 2 deg X-band CASA Dual-Polarized Phased Array Antenna (By: Jorge Salazar and Rafael Medina) pag#&#
  16. 16. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Effect of misalignment in Xpol 4 dB PUT PICTURE OF HORN AUT 17dB Setup of standard Ku-band Horn antenna Zo=4mm ro=2deg
  17. 17. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere How to improve the alignment • Use lasers and levels to verify the axis orthogonality • Use the electrical alignment technique developed for S-NF by NSI • Use the post-processing techniques such as Motion Tracking Interferometer developed also by NSI pag#&#
  18. 18. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Motion tracking interferometer • Measures time variant Az, El and Z motion between the AUT and probe, including effects of: – Thermal effects – Cables – Mechanical stress of Note: AUT. Motion Tracking Interferometer is a new • US patent #5,419,631 feature of NSI P-NF that cost $10K pag#&#
  19. 19. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Important points about alignment • Misalignment is more critical in Spherical than in Cylindrical and Planar scanners. • Misalignment in P-NF is critical for large array antennas that operate at higher frequencies • Misalignment is critical for low cross-polarization measurements • For S-and C-NF we can use the electrical alignment and for P-NF we can use the post-processing techniques such as Motion Tracking Interferometer • Beside there are several techniques to align the antenna and probe, those are expensive.
  20. 20. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Span setup and Sample Spacing • Span size (L) is calculated as function of D, Z, and θ. t=0.5λ sample • Z is the distance of the probe to the AUT, spacing in that is recommended use a value between X and Y (hight 3λ to 5λ. frequency) • D< 3λ is not recommended because the reflections of the probe and AUT and also because at than be possible capture evanesces waves that can affect the antenna performance (ripples). • D< 5λ, is ok but the span is larger and the Z measurement takes so long. • Sample spacing recommended is around 0.5 λ. Oversampling lower that S< 0.48 λ can introduce aliasing that can be represented as peaks in the sidelobes. NOTE: • CASCA NF range system scan size is 5’x5’ (1.5m x 1.5m)
  21. 21. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Truncation in P-NF • Truncation eliminates information about the AUT sidelobes beyond an angle determined by the measurement geometry and filters out all information about the evanescent modes. • Truncation of planar near-field data is the major source of uncertainty. • Advantages: reduces time, reduces scattering pag#&#
  22. 22. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Effect of the truncation in the FF antenna patterns With truncation at 50” No Truncation (Span 60”) MIRSL Ku-band Interferometer (Courtesy Anthony Swochak)
  23. 23. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Truncation effect in the scan AUT patterns No Truncation “Bad” Truncation
  24. 24. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Truncation effect in the scan AUT patterns No Truncation “Bad” Truncation
  25. 25. Radiation of the corporate fedLoadresistor MIRSL Ku-band IWRAP antenna
  26. 26. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Summary of Sampling and Truncation • Use ~0.5λ sample spacing in X and Y (for the highest frequency) • Use between 3 λ to 5 λ as separation between the probe and the AUT • Truncation can affect the antenna patterns principally in the far region of sidelobes. However in scanning antenna the beam pattern can be affected significantly • Perform first a full scan measurement and then define the truncation area when the fields are below -40dB using NN plots or fields projected to the surface. pag#&#
  27. 27. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Scattering and reflections inside the anechoic chamber • Absorbers are not perfect, they can provide an absorption up to 40dB (1-40GHz) • Sources of reflections: – AUT and probe – AUT and scanner/support – AUT and walls (including floor and ceiling) • Taper anechoic chambers minimize the reflection in walls J. Appel-Hansen, “Reflectivity level of radio anechoic chambers,” IEEE Trans. Antennas Propag., vol. AP-21, pp. 490–498, 1973.
  28. 28. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere RF Absorber and quiet zone room GROUND OR SHIELDED ROOM 6" PYRAMIDAL RF ABSORBER WITHOUT GROUND 6" PYRAMIDAL RF ABSORBER 55 3GHz 50 6GHz 10GHz 45 18GHz 40 35dB Reflectivity (dB) Reflectivity (dB) 35 30dB 30 25 20 15 10 0 10 20 30 40 50 60 70 80 Theta (deg)
  29. 29. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Horizontal Setup Effect of reflections in 2010 Azimuth patterns NO ABSOBERS IN FLOOR Horizontal Setup • Ku Band Interferometer Antenna 2011 • AUT size: 45”x1.25” • Frequency: 13.195 GHz- 13.295 GHzPatterns obtained using Slot Array Antenna designed by Ahtony Swochak.,“Development, implementation, and Characterization of a Ku Band
  30. 30. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Horizontal Setup Effect of reflections when 2011 AUT is in vertical position Vertical Setup 2011
  31. 31. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Vertical setup Effect of reflections when AUT is in vertical position Horizontal setup • X- Band CASA array antenna Size: 22”x12” • Frequency: 9.36 GHz
  32. 32. casa Engineering Research Center for CollaborativeAdaptive Sensing of the AtmosphereTechniques to estimate the reflections in anechoicchamber in NF NSI systema. Self comparison technique: The multipath effect can be identified by observing the changes in the FF- patterns changing the NF test parameters such as: • AUT-to-probe separation • AUT-to-scanner separation • AUT-to-wall separation • AUT orientation in Az and El • AUT lateral movement • This test requires the probe translation stage in Z (~$7.5K) pag#&# EVALUATING NEAR-FIELD RANGE MUTI-PATH., Gregory F. Masters., Nearfield Systems., 1330 E. 223rd St. #524 Carson, CA 90745
  33. 33. casa Engineering Research Center for CollaborativeAdaptive Sensing of the Atmosphere Techniques to estimate the reflection in anechoic chamber in NSI NF system 2’x2’ metal b. MARS: Mathematical Absorber obstruction Reflection Suppression, is a post- procesing technique developed by AUT NSI useful to mitigate unwanted Planar slot reflections. waveguide probe antenna MARS analisis of the measured data and a special mode filtering process to suppress the undesirable scattered signals. The technique is a general technique that can be applied to any S –NF and C-NF range systems. NOTE: Add this feature to CASCA NF range system requires additional cost of $15K pag#&#IMPROVING AND EXTENDING THE MARS TECHNIQUE TO REDUCE SCATTERING ERRORS, Greg Hindman & Allen C. NewellNearfield Systems Inc. 19730 Magellan Drive Torrance, CA 90502
  34. 34. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Summary of Reflections in the room • Absorbers are not perfect, the reflectivity values depend on the size, frequency and installation. • Reflectivity of the absorbers are critical for lower frequencies . • It is important to keep in mind that the reflections of waves on the ground, ceiling and uncover scanner support can affect the main beam, sidelobes and cros-pol patterns of the AUT considerably. • Two common techniques can be used to minimize the scattering and reflections inside the room. – In P-NF use the Z-spacing – In S-NF, C-NF use MARS
  35. 35. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Probes and probe correction • Probe types: There are several probe types that you can use: OEWP, Dipoles, MS Patches, Horns, Conical antennas, etc. Dual -log periodic antennas 3GHz- • Probe correction: This is the The QR-1 is a broadband, dual polarized quad-ridged horn. It 17GHz process of removing the effect operates from 750 MHz to 6 GHz. of the pattern probe in the AUT pattern (Co and Xpol components). • Probe data are calibrated and certified by entities such as National Institute of Standards MS Patch antenna & Technology (NIST) OEWP antenna probes
  36. 36. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere How the probe can affect the AUT patterns in Planar NF AUT OEWPREF. PROBE CORRECTION EFFECTS ON PLANAR, CYLINDRICAL AND SPHERICAL NEAR-FIELD MEASUREMENTS GREG HINDMAN, DAVID S. FOOSHE
  37. 37. casa How the probe can Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere affect the AUT patterns in Cylindrical NF AUT OEWP pag#&#REF. PROBE CORRECTION EFFECTS ON PLANAR, CYLINDRICAL AND SPHERICAL NEAR-FIELD MEASUREMENTS GREG HINDMAN, DAVID S. FOOSHE
  38. 38. casaHow the probe can Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere affect the AUT patterns in Spherical NF AUT OEWPREF. PROBE CORRECTION EFFECTS ON PLANAR, CYLINDRICAL AND SPHERICAL NEAR-FIELD MEASUREMENTS GREG HINDMAN, DAVID S. FOOSHE
  39. 39. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere How the probe can affect the AUT cross-polar patterns Θ=45 deg Θ=45 deg Θ=45 deg Xpol: 23dB Planar NF Cylindrical or Θ=0 deg Xpol: -40dB Spherical NF REF. PROBE CORRECTION EFFECTS ON PLANAR, CYLINDRICAL AND SPHERICAL NEAR-
  40. 40. casa Engineering Research Center for CollaborativeAdaptive Sensing of the Atmosphere Leakage in room • The main source of leakage in near-field measurements are produced by cables, connectors and bad connections with the AUT and the probe. • Leakage from cables, connectors and the RF source can be identified and reduced by using well shielded cables, tightening connectors and placing instruments in shielded enclosures. • One way to verify the leakage between cables, connectors and the probe or antenna is terminate first the AUT and measure in S-C or P NF.
  41. 41. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Error budget for -30dB SLL measurement EVALUATING NEAR-FIELD RANGE MUTI-PATH., Gregory F. Masters., Nearfield Systems., pag#&# 1330 E. 223rd St. #524 Carson, CA 90745
  42. 42. casa Engineering Research Center for CollaborativeAdaptive Sensing of the Atmosphere Antenna range systems at UMASSCASCA antennas Lab. has two range systems. • NSI Taper FF range system – Frequency Range : 1-40 GHz, – Absorber size: 6” (CF-6, 32dB@3GHz-50dB @50GHz) – Length: 21’ (6.4m) – 1 axes-positioner – Base on PNA 8360 (1-40GHz) • NSI S-C and Planar NF range – Frequency Range : 1-40 GHz, – Absorber size: 8” – (30dB @1GHz-50dB @50GHz) – Length: 14’x10’ (4.2mx3.0m) – 1 axes-positioner for S and C – Only in operates in CW mode – Base on PNA 8360 (1-40GHz) pag#&#
  43. 43. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere CASA Phase-tiltantenna azimuth Patterns V-pol
  44. 44. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere CASA Phase-tiltantenna azimuth Patterns V-pol
  45. 45. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere CASA Phase-tiltantenna azimuth Patterns V-pol
  46. 46. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere CASA Phase-tiltantenna azimuth Patterns V-pol
  47. 47. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere H and Hx at NN-FF of PTAA (64x32), θ=0º, SC CASA Phase-tiltantenna azimuth Patterns V-pol
  48. 48. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere CASA Phase-tiltantenna azimuth Patterns H-pol
  49. 49. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere CASA Phase-tiltantenna azimuth Patterns H-pol
  50. 50. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere CASA Phase-tiltantenna azimuth Patterns H-pol
  51. 51. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere CASA Phase-tiltantenna azimuth Patterns H-pol
  52. 52. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere H and Hx at NN-FF of PTAA (64x32), θ=0º, SC CASA Phase-tiltantenna azimuth Patterns H-pol
  53. 53. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere CASA Phase-tilt antenna elevation patterns Measured patterns of 32x1 linear array in LRU (32X18) V-port H-Port Parameter Value@9.36GHz Parameter Value@9.36GHz BW 3.81 deg BW 3.62 deg SLL1(L/R) -29/-26.5 dB SLL1(L/R) -23.2/-22.5 dB Emax(dB) -43.83 dB Emax(dB) -43.30 dB Xpol_brodside -34 dB (rel) Xpol_brodside -38.7 dB (rel) ICPR2 -34.4 ICPR2 -34.0 Measured results: • RL better than -13 dB at Resonant frequencies for H and VPatch layer Foam layer • Impedance bandwidth: 200 MHz at RL of -10 GHz (improved in 80 MHz) Fed layer • Beam pattern bandwidth: 100 MHz (improved in 40 MHz) Reflector layer • Isolation port -27 dB
  54. 54. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Recommendation for an antenna measurement in NF system • Never perform an antenna measurement without a reference of patterns of the AUT (simulated, previous measurement). • Understand first how the errors (fabrication, random errors) can affect the antenna patterns. • Before performing a measurement, make sure that scattering and reflection in the room are low enough to avoid contamination of the AUT measurements. • Make sure that the size of the scanner is larger than the span required for the AUT. • Perform a stability test ( to evaluate the effect of mechanical stress and temperature versus time). • Perform a leakage test to be sure that cables are well connected with the AUT and receiver. • Keep in mind that the cross-polar measurements are very sensitive to alignment and also reflections in the room. • Perform an antenna test plan and discuss details with your advisor or person who has experience doing this type of measurement. • Call me at 413-123456 if you need some help. I will charge you a beer/hour.
  55. 55. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Consideration for a good Antenna Plan Test • Have preliminary results of AUT (simulations previous meas. Paterns) • Estimation the time for each specific test measurement • Have in mind how the position errors can affect your measurments. • Take in consideration the alignment of AUT and probe • Do a stability test (mechanical stress, temperature) • Monitoring the SNR vs Frequency (for large bandwidth antenna) • Take in consideration the scattering issues at lower frequencies (more if you wan very low cross-pol values ( better that 25dB) • Take in consideration the Probe data to be used to correct the probe effect • Coordinate systems (Az/Ele, Theta/Phi, X /Y) pag#&#
  56. 56. casa Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere Thanks In this Picture Jorge Salazar and Rafael Medina taking antenna patterns of CASA dual-polarized phased -Array antenna (Feb. 2011) pag#&#

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