Current Antenna Research at NIST

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1 Current Antenna Research at NIST Perry Wilson Electromagnetics Division National Institute of Standards and Technology B O U L D E R, C O L O R A D O 1

2 NIST Organizational Structure B O U L D E R, C O L O R A D O 2

3 Electromagnetics Division Division Office Perry Wilson, Div. Chief (Acting) RF Electronics Group Ron Ginley, GL RF Fields Group Mike Francis, GL (Acting) Magnetics Group Ron Goldfarb, GL Fundamental Microwaves Materials Properties High Frequency Devices EM Fields Antennas Wireless Systems Nano-Magnetics Bio-Magnetics Superconductivity B O U L D E R, C O L O R A D O 3

4 Antennas Project Main Tasks Antenna parameter calibration services (SP250) Near-field theory Spherical near-field uncertainty analysis RCS theory, artifacts, and range certification RFID THz Antenna standards and intercomparisons Short Courses B O U L D E R, C O L O R A D O 4

5 Antenna Parameters Gain, Pattern, Polarization 2 planar near-field ranges Cylindrical near-field range Spherical near-field range 2 Extrapolation ranges Calibration services 2 GHz to 110 GHz Research in progress to extend services to 600 GHz B O U L D E R, C O L O R A D O 5

6 Antenna Metrology at NIST Focus has been on near-field antenna measurments. began in 1955 as a byproduct of speed of a light experiment B O U L D E R, C O L O R A D O 6

7 Antenna Metrology at NIST Interferometer required a diffraction correction. Kerns developed a plane wave scattering matrix formalism to calculate the diffraction correction. The application required measurments of the amplitude and phase of the EM fields close to the aperture of the antenna. This was then transformed to the far-field to determine the correction. Around 1960 the invention of the laser ended the microwave speed of light experiment. B O U L D E R, C O L O R A D O 7

8 Antenna Metrology at NIST Speed of light scanner adapted to 1.2 m square planar near-field scanner (PNFS). B O U L D E R, C O L O R A D O 8

9 Dissemination of PNFS Initially met with considerable skepticism. non-intuitive versus direct far-field measurement too theoretical requires extensive numerical processing (computers were weak at the time) uncertainties unclear Now NFS is the accepted method ranges world wide planar, cylindrical, spherical ranges, and more B O U L D E R, C O L O R A D O 9

10 Kern s Monograph B O U L D E R, C O L O R A D O 10

11 NIST MMW Planar NF Range 2.5 m x 2.5 m GHz Scanner nominally aligned to 25 GHz (λ/50) Implemented position correction theory B O U L D E R, C O L O R A D O 11

12 NIST Spherical + Cylindrical NF Range B O U L D E R, C O L O R A D O 12

13 Fully Anechoic Chamber B O U L D E R, C O L O R A D O 13

14 NIST 40 GHz Extrapolation Range B O U L D E R, C O L O R A D O 14

15 NIST 110 GHz Extrapolation Range B O U L D E R, C O L O R A D O 15

16 Current Research Refine uncertainty analyses Range comparisons Ku-band intercomparison of NIST ranges GTRF - K23.F (antenna gain, GHz, NIST pilot lab) W-band KRISS, NPL intercomparison Test volume evaluation Extend gain, polarization, pattern capability to 500 GHz Position error correction theory and application Develop alignment techniques Develop scanning techniques B O U L D E R, C O L O R A D O 16

17 NIST Range Intercomparison Same antenna tested in the NIST planar, cylindrical, and spherical ranges Ku-band Cassegrain Antenna (16 GHz) B O U L D E R, C O L O R A D O 17

18 NIST Range Intercomparison B O U L D E R, C O L O R A D O 18

19 NIST Range Intercomparison B O U L D E R, C O L O R A D O 19

20 Intercomparison with KRISS, NPL W-band (75 GHz 110 GHz) Two horn antennas tested on extrapolation ranges B O U L D E R, C O L O R A D O 20

21 Intercomparison with KRISS, NPL B O U L D E R, C O L O R A D O 21

22 Intercomparison with KRISS, NPL B O U L D E R, C O L O R A D O 22

23 Test Volume Characterization Goal: define fields in an antenna range test volume, e.g., a compact range. Problem: probing the test volume along linear scans gives limited information. Solution: precisely acquire actual grid positions (dynamic laser tracker) and analytically correct near-field to far-field calculation. B O U L D E R, C O L O R A D O 23

24 Compact Range B O U L D E R, C O L O R A D O 24

25 Exterior Spherical NF Scan Looking inward B O U L D E R, C O L O R A D O 25

26 Interior Spherical NF Scan Looking outward B O U L D E R, C O L O R A D O 26

27 Imaging External Scattering Objects B O U L D E R, C O L O R A D O 27

28 Position Error Correction Goal: acquire data over a perfect x-y grid. Problem: some error in positioning during data acquisition. Solution: precisely acquire actual grid positions (dynamic laser tracker) and analytically correct near-field to far-field calculation. B O U L D E R, C O L O R A D O 28

29 Position Error Correction Normal equations: Aξ = b A = b = Q Q H H where Q w Non-uniform case, conjugate gradient solution: d d (0) ( j+ 1) = r(0) = b Aξ = r ( j+ 1) + r ( j+ 1) r ( j) 2 2 d ( j) B O U L D E R, C O L O R A D O 29

30 Dynamic Laser Tracker

31 Position Error Correction B O U L D E R, C O L O R A D O 31

32 Position Error Correction H-plane patterns at 4 GHz error < 0.28λ error < 1.10λ B O U L D E R, C O L O R A D O 32

33 Alignment Above 110 GHz Goal: align antennas above 110 GHz. Problem: current methods using theodolites no longer practical. Solution: use optical techniques and pixel resolution to align antennas. B O U L D E R, C O L O R A D O 33

34 NIST Overlay Imaging Aligner (OIA) Developed to aid in the mechanical alignment of antenna components in the mm-wave and THz frequency regimes where dimensions of the wavelength pose significant challenges for alignment. An integrated alignment laser and simultaneous two-scene imager allows waveguide, horns and lenses to be viewed and aligned simultaneously to a common optical axis. The detector array provides real time digital images of the antenna component alignment and can be processed in software for highly accurate and precise antenna component alignment at the pixel level. Each pixel corresponds to ~50 microns at the antenna under test. B O U L D E R, C O L O R A D O 34

35 Alignment Set-up B O U L D E R, C O L O R A D O 35

36 OIA Example: WR-03 Horns Viewing both WR-03 horns along a common axis. Misalignment of horns is easily measured on pixel array to 50 micron resolution. Allows real-time alignment of horns and waveguides. Pins corners B O U L D E R, C O L O R A D O 36

37 OIA Video Demo ELECTROMAGNETICS DIVISION B O U L D E R, C O L O R A D O 37

38 NF Scanning Above 110 GHz Goal: perform NF scanning above 110 GHz. Problem: precision rotary joints may not be possible above 180 GHz. Solution:??? B O U L D E R, C O L O R A D O 38