Millimetre Spherical Wave Antenna Pattern Measurements at NPL Philip Miller May 2009
The NPL Spherical Range The NPL Spherical Range is a conventional spherical range housed within a 15 m by 7.5 m by 7.5 m temperature controlled anechoic chamber It is equipped with a HP 8510C RF system operating up to 110 GHz. This is being upgraded to an Agilent PNA-X System
The NPL Spherical Range - Layout Transmit Tower Ram Screens Receive Positioner System Range Pit Transmit Tower Rails
The NPL Spherical Range - Positioner 1m maximum with 0.6m Travel 3.7m Possesses Alignment Aids Counterbalance Adjustable Slide
The NPL Spherical Range - Photograph
Millimetre Wave Measurements Major Error Sources RF Stability Errors Equal Signal and Reference Path Lengths Temperature Controlled Chamber Stability better than 1 deg at 72 GHz Can be tracked using a Tie Scan Antenna Positioner Errors High Accuracy Positioner System Antenna Stability Errors Possibly More of a Problem in Polar Mode
Millimetre Wave Measurements Positioner Errors Three Sources of Error Misalignment Errors Manufacturing Errors Positioning Errors Examine the effects of the errors on a 42 dbi directivity antenna
Millimetre Wave Measurements Misalignment Errors Bottom Turntable can be aligned to 0.003 degree Large effect due to Tower Axes can be aligned to 0.1 mm Phase error ε p = 25 sin(θ) deg at 94 GHz Reduces to 0.5 deg over main beam area (Range Length = 6 m)
Millimetre Wave Measurements Manufacturing Errors Axis Positioning Errors and Axis Tilt Errors Tilt Error (Degs) 0.005 0.004 0.003 0.002 0.001 0-0.001-0.002-0.003-0.004-0.005 Azimuth Axis Tilt Error Fully Loaded 0 90 180 270 360 Horizontal Plane Vertical Plane Tilt Error (degs) Elevation Axis Tilt Error 0.003 0.002 0.001 0-0.001-0.002-0.003-180 -120-60 0 60 120 180 Across Slide Along Slide Position (Degs) Position (degs)
Millimetre Wave Measurements Manufacturing Errors Uncertainty Budget Error Quantity Uncertainty in Horizontal Plane Positional Uncertainty in Horizontal Plane, mm Azimuth Position Wobble 0.004 deg 0.070 Azimuth Positioner Radial Runout 0.025 mm 0.025 Azimuth Positioner Axial Runout 0.008 mm 0.008 Elevation Position Wobble 0.0025 deg 0.131 Elevation Positioner Radial Runout 0.05 mm 0.050 Elevation Positioner Axial Runout 0.02 mm 0.017 95% Probability 0.32
Millimetre Wave Measurements Manufacturing Errors Error Model Largest Major Frequency Component = 3 * θ Error Bounded by 1 mm in Azimuth Error Bounded by 2 mm in Elevation ( 3φ + φ ) sin( θ ) + 22*sin( 3* ( θ ) + ) Pherror = 11*sin 0 90 θ0 degrees
Millimetre Wave Measurements Positioning Errors Positioning Errors are due to two effects: - Stopping Window of Uncertainty when a Positioner is Sent to a Point Trigger Timing Error when Acquiring with a Moving Positioner For the Scan Axis Bus Delay = 15 ms corresponding to an 0.075 deg uncertainty For Step Axis Positioning Uncertainty = 0.005 deg
Millimetre Wave Measurements Antenna Near-Field Amplitude Data R = 5 m Near Field Theta Cut - Amplitude -10.00-20.00-30.00 Level db -40.00-50.00-60.00-70.00-80.00 50 60 70 80 90 100 110 120 130 Angle Degrees
Millimetre Wave Measurements Antenna Near-Field Phase Data R = 5 m Near-Field Theta Cut - Phase 0.00-100.00-200.00 Phase Degrees -300.00-400.00-500.00-600.00-700.00-800.00-900.00-1000.00 70 75 80 85 90 95 100 105 110 Angle Degrees Rate of Change of Phase = 70 deg/deg at 1 deg Shows a 36 mm offset at 94 GHz
Millimetre Wave Measurements Error Analysis Techniques Transform Data with and without Errors Calculate the effective error signal from ε ( ) ( θ,φ) = 20.*log 10^ ( P ( θ,φ) /20) 10^ ( P ( θ,φ) /A /20) Re-pointing carried out using Lagrange Interpolation N PN(θ,φ) is the magnitude of the normalised error free pattern Pe(θ,φ) is the magnitude of the non-normalised pattern with errors Ae is the normalising amplitude constant chosen to minimise the peak error signal e e
Millimetre Wave Measurements Manufacturing Errors Phi Plane Manufacturing Errors Phi - Null on Boresight 0.00-10.00-20.00 Level db -30.00-40.00-50.00 No Error Case Error Signal Error Signal Repointed -60.00-70.00-80.00 50 70 90 110 130 Angle Degrees
Millimetre Wave Measurements Manufacturing Errors Theta Plane Manufacturing Errors Theta - Null on Boresight 0.00-10.00-20.00 Level db -30.00-40.00-50.00 No Error Case Error Signal Error Signal Repointed -60.00-70.00-80.00 50 70 90 110 130 Angle Degrees
Millimetre Wave Measurements Alignment Errors Phi Plane Alignment Error Phi 0.00-10.00-20.00 Level db -30.00-40.00-50.00 No Errors Error Signal -60.00-70.00-80.00 50 60 70 80 90 100 110 120 130 Angle Degrees
Millimetre Wave Measurements Alignment Errors Theta Plane Alignment Error Theta 0.00-10.00-20.00 Level db -30.00-40.00-50.00 No Errors Error Signal -60.00-70.00-80.00 50 60 70 80 90 100 110 120 130 Angle Degrees
Millimetre Wave Measurements Positioning Errors Large Error Case Modelled as a Timing Error between 0 to 15 ms at an axis speed of 5 deg/s Errors assumed to a have a Rectangular Distribution Both Amplitude and Phase Errors Modelled Small Error Case Limited to 0.005 degree equivalent to Step Acquisition Case
Millimetre Wave Measurements Positioning Large Errors Phi Plane Timing Errors Phi - Large Errors 0.00-10.00-20.00 Level db -30.00-40.00-50.00 No Errors With Errors Error Signal -60.00-70.00-80.00 50 60 70 80 90 100 110 120 130 Angle Degress
Millimetre Wave Measurements Positioning Large Errors Theta Plane Timing Errors Theta - Large Errors 0.00-10.00-20.00 Level db -30.00-40.00-50.00 No Errors With Errors Error Signal -60.00-70.00-80.00 50 60 70 80 90 100 110 120 130 Angle Degrees
Millimetre Wave Measurements Positioning Small Errors Phi Plane Timing Errors Phi - Small Errors 0.00-10.00-20.00 Level db -30.00-40.00-50.00 No Errors Error Signal -60.00-70.00-80.00 50 60 70 80 90 100 110 120 130 Angle Degrees
Millimetre Wave Measurements Positioning Small Errors Theta Plane Timing Errors Theta - Small Errors 0.00-10.00-20.00 Level db -30.00-40.00-50.00-60.00 ` No Errors Error Signal -70.00-80.00 50 60 70 80 90 100 110 120 130 Angle Degrees
Millimetre Wave Measurements Positioning Errors Observations The Error Signal should reduce by ε red = 20.*log(.075/.005) = 24dB Actual Reduction Phi Cut reduction = 24 db to 55 db Theta Cut reduction = 11 db to 50 db (Possible Correlation between Successive Cuts)
Millimetre Wave Measurements Positioning Errors Observations Actual Phi Positioning Errors Step Case Phi Angle Error Distribution 0.07 0.06 0.05 Probability 0.04 0.03 0.02 0.01 0-0.002-0.001 0 0.001 0.002 0.003 0.004 0.005 0.006 Error Degrees
Millimetre Wave Measurements Positioning Errors Observations Actual Theta Positioning Errors Step Case Elevation Theta Angle Setting Accuracy Case -0.003-0.0035-0.004-0.0045 Error Degrees -0.005-0.0055-0.006-0.0065-0.007-0.0075-0.008 0 10 20 30 40 50 60 70 80 90 100 110 Theta Angle Degrees
Millimetre Wave Measurements Positioning Errors Conclusions Receiver Timing Error Largest Source of Uncertainty In Step Scan Mode errors at 100 GHz Gain Uncertainty better than 0.05 db Sidelobe Uncertainty better than 0.4 db at 40 db NPL is Upgrading its Receiver to an Agilent PNX reducing Timing Error from 15 ms to 60 μs. Range could give Excellent Result up to 300 GHz