Recent Advances in Antenna Measurement Techniques at theDTU-ESA Spherical Near-Field Antenna Test Facility

Olav Breinbjerg, Sergey N. Pivnenko, Oleksiy S. Kim, and Jeppe M. NielsenDepartment of Electrical Engineering, Technical University of Denmark

URSI GASSBeijing, China, August 16-23, 2014

URSI GASS 20142

DTU-ESA Facility

ESA external reference laboratory• high-accuracy measurements• DTU-ESA standard gain horns• DTU-ESA VAST antennas

Antenna calibration/measurement• ESA and ESA contractors• European academia / industry• DTU research and education

European School of Antennas• Advanced Spherical Near-Field

Antenna Measurement Techniques

• 2007/2009/2011/2013

15m x 12m x12m

• MI-3103 signal source• MI-1797 receiver• DTU/MVG/TICRA probes• DTU/TICRA NF-FF software• 400 MHz – 40(60) GHz• AUT: max. 6 m and 250 kg

URSI GASS 20143

Facility Validation Standard Antenna(s)

DTU-ESA 12GHz VAST Antenna

URSI GASS 20144

High-Accuracy Antenna Measurements ESA Earth Observation Programme

SMOS 1.4GHz SENTINEL-1 5.4GHz BIOMASS 435MHz

Uncertainty (3dB,1)Magnitude: 0.05dBPhase: 0.33deg.

Uncertainty (3dB,3)Directivity: 0.03dBGain: 0.1dB

Uncertainty (1)Gain: 0.15dB

URSI GASS 20145

SMOS – Multiple Reflections Compensation

/2

Multiple reflections between AUT and probe are not accounted for by theory -> uncertainty estimate

Very effective approach for cancellation of multiple reflections – for on-axis as well as off-axis AUTs

URSI GASS 20146

BIOMASS – Measurements and CaculationsMethodology: measurement of feed+support radiation followed by calculation of reflector+satellite radiation

IE/MOM calculations show negligible reflector-satellite interactions

Measurement uncertainties for different feed+support configurations?

1A1B1C

2

3Directivity Uncertainty - Feed configuration 2

Source 1 (dB)

Feed measurement w/wo test structure 0.13/0.03

Reflector-satellite interactions 0.01

Reflector support arm influence 0.01

Feed model (configuration 2) 0.04

Deployment accuracy 0.03

Reflector surface modelling 0.04

Numerical tool 0.01

Total w/wo test structure 0.15/0.07

Gain Uncertainty - Feed configuration 2

Source 1 (dB)

Directivity 0.07

Feed radiation efficiency 0.09

SGH radiation efficiency 0.10

Feed mismatch correction 0.01

SGH mismatch correction 0.01

Signal source mismatch 0.04

Drift 0.03

Cable variations 0.02

Reflector radiation efficiency -

Total 0.16

reflfeedDG

URSI GASS 20147

Sentinel - Two Gain Measurement TechniquesPattern based on average of 4 measurements:• 2 measurement distances

- multiple reflections• 2 signal generator power levels

- receiver non-linearityGain based on average of 2 measurements:• Near-field substitution• Finite-distance substitution

URSI GASS 20148

Higher-Order Probe Correction I

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Conical horns are first-order probes but they1) have a narrow bandwidth, 2) become heavy/large below 1GHz, and3) may possess residual higher-order modes

First-order probes (= ±1) facilitate efficient and stable probe correction

URSI GASS 20149

Higher-Order Probe Correction II

First-order Probe:SMOS

Higher-orderProbe:0.15 offset square WG

AUT: 8 offset 1.4-1.5 GHz

URSI GASS 201410

Scalable 1:3 Bandwidth Dual-Port Probes I

Specifications:• 1:3 bandwidth• frequency scalable• mechanically stable• uniform AUT illumination• minimize wall reflections• minimize support structure scattering

Narrow spacing for:• bandwidth• cross polarization• port coupling• pattern symmetry

Open boundary quad-ridge horn

1-3 GHz version

Mass: 3.2 kgWidth: 0.40 mHeight: 0.46 m Material: Al

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URSI GASS 201411

Scalable 1:3 Bandwidth Dual-Port Probes II400-1200 MHz version

Mass: 22.5 kgWidth: 1mHeight: 1.15mMaterial: Al and CFRP

URSI GASS 201412

Superdirective First-Order Probe IFirst objective:435 MHz first-order single-port probe for experimental validation of 400-1200 MHz dual-port probe

400-1200 MHz probe

Second objective:A small and light-weight first-order probe for frequencies below 1 GHz

Mass: 2 kgWidth: 0.72mHeight: 0.185Material: Al and RO4003C

435 MHz magnetic dipole probe

Permittivity anisotropy

0.15

0.27

CLL

Self-resonant!

URSI GASS 201413

Superdirective First-Order Probe II

D = 9.2 dBG = 7.1 dBrad = 61%

URSI GASS 201414

Other Recent AdvancesAntenna diagnostics DTU-ESA mm-wave VAST antenna

– for K/Ka/Q/V-bands

Machine-vision mechanical alignment• Autocollimator• Electronic level• Laser tracker• Stereo camera• CMMs

URSI GASS 201415

ThankYou