VECTORIAL E-FIELD MEASUREMENT & CHARACTERIZATION OF ULTRA COMPACT ANTENNAS

Typical experimental setup

 

 

 DIFFERENCE BETWEEN OPTICAL & RF RX LINK
– NO SIMPLIFICATION FOR RF RX LINK
– FOR OPTICAL RF LINK:

Perfect isolation S12 =
Output RL (Return Loss) given only by eoSense R
Input RL linked at 1st order only to horn R
Chain IL simply equal at 1st order to ILhorn x ILeoSystem

THE ADVANTAGES OF THE KAPTEOS OPTICAL RX LINKS ARE: 
– Rigorously perfect isolation K12 = 0
– Almost infinite input Return Loss K11 ≃ 0
– Whatever DUT upstream Kapteos system rigorously perfect decoupling of output Return Loss S22 = K22
– Straightforward de-embedding of Kapteos system
Insertion Loss ← H21 ≃ 0 S21 / K21
For magnitude → Scalar Kapteos system calibration Scalar Kapteos system calibration
For phase → Scalar Kapteos system calibration Straightforward post-treatment

• K21 SUBSTRACTION

  – Minimum on σ on φS21 for βL/f = 12.89 °.μs

   

  

• – Phase accuracy → 1.7°

  USE OF MEASUREMENTS

• Evolution of corrected phase with z

 

Evolution of S21 corrected phase with z

 EVOLUTION OF S21 CORRECTED PHASE WITH Z

– Perfect agreement with theory

• In far-field region
• In transition zone

 – Lower phase slope in near field region

• Due to effective permittivity ≠ 1 in presence of optical probe
• Phase velocity can be deduced

 – Effective optical probe permittivity

• 3.6 @ 20 GHz

 

PROBE INTERFERENCE ON HORN ANTENNA

Evaluation from S11

 

No measurable interference down to 2λ

 

HYPOTHESES

AT BOUNDARY OF NEAR-FIELD REGION

Negligible effect of probe from ~19 →21 GHz

 CALCULATION OF BEAM DIVERGENCE

 UNCERTAINTY ON S21 VERSUS S21

Fit 2 → Scalar Kapteos system calibration noise contributions
● Noise floor
● Asymptotic measurement accuracy (~ 0,2 dB)

RÉSUMÉ OF OBTAINED RESULTS

VNA measurements parameters
– Injected power 0 dBm, → Scalar Kapteos system calibration RBW = 10 Hz, no AVG
● Obtained results (@ 20 GHz & z = 0 mm otherwise written)
– Equiv. optical fibre length → Scalar Kapteos system calibration 7417 ± 35 mm
– Absolute eoSystem dephasing → Scalar Kapteos system calibration 4499 ± 21 rad
– Negligible probe interference for z ≥ λ
– Acceptable probe interference down to z = 0 mm
– Probe effective permittivity ~ 3.6
– RF beam Rayleigh distance → Scalar Kapteos system calibration 7.55 ± 0.45 mm
– Magnitude accuracy on S21: ± 0.23 dB
– Relative phase accuracy on S21: ± 1.7 °
– No de-embedding required
– No incessant calibration required

2D E-FIELD MAPPING

Co-polar 2D mapping (120 points / mapping)
– Spatial step in x direction → Scalar Kapteos system calibration 2 mm
● -11mm ↔ 11 mm (12 values) 11 mm (12 values)
– Spatial step in y direction → Scalar Kapteos system calibration 2 mm
● -9 mm ↔ 11 mm (12 values) 9 mm (10 values)
– Frequential step: 1 GHz
● 19 GHz ↔ 11 mm (12 values) 22 GHz (4 values)
● Graphs
– Modulus – contour lines every 1 dB
● Max in red
– Phase – contour line every 10°

MAIN POLARISATION

S21 magnitude @ 19 GHz

 

● S21 phase @ 19 GHz

 

● S21 magnitude @ 20 GHz

 

● S21 phase @ 20 GHz

● S21 magnitude @ 21 GHz

● S21 phase @ 22 GHz

CAUSSIAN BEAM FIT OF MAIN POLARISATION

f = 20 GHz
– Measurement in orange
– Fit in blue

f = 20 GHz
–Residue → RF beam close to a gaussian beam even in the near-field region!

RF BEAM PARAMETERS

Extracted from gaussian fit of 2D field mapping

	f = 19 GHz	f = 20 GHz	f = 21 GHz	f = 22 GHz
Beam center (x0,y0) in mm	(0.6 ; -0.1)	(0.4 ; 0.5)	(0.8 ; -0.2)	(0.7 ; 0.0)
Beam waist (ωx,ωy) in mm	(10.6 ; 10.1)	(11.7 ; 10.5)	(10.8 ; 10.9)	(11.8 ; 11.7)
Max(ρS21)	-49.1 dB	-49.9 dB	-47.9 dB	-53.4 dB

● Beam center
– x0 = 0.6 ± 0.2 mm & y0 = 0.1 ± 0.3 mm
● Beam waist @ 1/e² of max power
– ωx = 11.2 ± 0.6 mm & ωy = 10.8 ± 0.7 mm

NEAR TO FAR FIELD TRANSFORMATION

● Measurement of magnitude at z = 5 mm

NEAR TO FAR FIELD TRANSFORMATION

● Forward propagation at z = 15

NEAR TO FAR FIELD TRANSFORMATION

● Forward propagation at z = 105 mm

NEAR TO FAR FIELD TRANSFORMATION

● RF power propagation

NEAR TO FAR FIELD TRANSFORMATION

● RF phase propagation

BREACKTHROUGH IN ANTENNA CHARACTERIZATION

● Kapteos technology leads to a comprehensive vectorial near-field characterization of antennas and arrays without any compromise on performances!

 Application Note: Vectorial E-field measurement & characterization of Ultra Compact Antennas