Course on Microwave Measurements - unipv · Microwave Measurements 2014/15 Prof. Luca Perregrini...

Microwave Measurements 2014/15 Prof. Luca Perregrini Antenna measurements, pag. 1

Prof. Luca Perregrini

Dept. of Electrical, Computer and Biomedical EngineeringUniversity of Pavia

e-mail: [email protected]: microwave.unipv.it

Course on Microwave Measurements

Antenna measurements


Summary

• Why antenna measurements?

• What do we measure?

• How do we measure?


• To verify the design• To tune the antenna components• To evaluate the production yield• To routinely check the antenna performance

Why antenna measurements?

AUT = Antenna Under Test


Radiation characteristics• Radiation pattern: main lobe beamwidth, main lobe direction,

side lobes levels/directions, gain• Polarization: axial ratio, cross polarization

Input characteristics• Reflection coefficient

System parameters• Equivalent Isotropic Radiater Power (EIRP), Gain to antenna

temperature ratio (G/T)

Mechanical properties

Parameters of interest


The radiation pattern represents the normalized spatial powerdistribution radiated by the antenna

• Radiation intensity: K(θ,φ) = dPirr / dΩ [W/sterad]

• Directivity: D(θ,φ) = K(θ,φ) / Kmean =

• Gain: G(θ,φ) = η D(θ,φ) =

4//

irr

irr

PddP

4//

in

irr

PddP

Radiation pattern

The radiation pattern is the plot of G(θ,φ)/Gmax(equivalent to K(θ,φ)/Kmax)


Radiation pattern

Polar representation (2D)

LinearLogaritmic (dB)


Radiation pattern

Cartesian representation (2D)

LinearLogaritmic (dB)


Radiation pattern

Spherical representation (3D)


Radiation pattern

Cartesian representation (3D)


Radiation pattern

Contour plot (3D)


Radiation pattern

Relevant parameters


ITU mask

Radiation pattern

International Telecommunication Union (ITU) masks


Polarization


Relevant field zones


4 21

2

GGrP

P

TX

RX

Friis formula


Antenna measurement setup

Outdoor far-field• Elevated range• Ground reflection range

Indoor (anechoic chamber) far-field• Standard AUT-probe system• Compact antenna test range (CATR)

Indoor (anechoic chamber) near-field• Planar scanning system• Cylindrical scanning system• Spherical scanning system


Elevated range AUT (RX)Calibrated probe(TX)

AUT moving system

• Flat land• AUT/probe monted on high towers/buildings at far-field distance• Probe must guarantee uniform field distribution on AUT (not critical)• If possible, scatterers placed on the ground reflection area

Outdoor far-field


Outdoor far-field

Elevated range


Outdoor far-field

Elevated range


Outdoor far-field

Ground reflection range AUT (RX)

Calibrated probe(TX)

AUT moving system

• Flat land• The ground reflection enhances phase uniformity on the AUT• AUT/probe monted on high towers/buildings at far-field distance• The AUT is positioned on the first interference lobe between the

probe and the ground mirror reflection


Outdoor far-field

Ground reflection range


Outdoor far-field

Calibration methods


Outdoor far-field

Pros/Cons


Indoor far-field

Anechoic chamber

Completely shielded environment covered by electromagnetic absorbing panels

AUT (RX)Calibrated probe(TX)

AUT moving system


Indoor far-field

Anechoic chamber


Indoor far-field

Pyramidal Anechoic chamber


ETS-Lindgren Wireless Test Chambers

(400 MHz to 6000 MHz)

Sat Com Electronics Antenna Tapered Chamber(500 MHZ 40 GHz)

SBH feed antenna

Test zone Feed section

Indoor far-field

Pyramidal Anechoic chamber


Indoor far-field

Semi-Anechoic chamber


Indoor far-field



Indoor far-field



maxmin fff

Indoor far-field measurement details

Frequency constraints

• Dimensions of the anechoic chamber

• Reflection of the anechoic material

• Attenuation

• Instrumentation

• Antenna probe


maxmin fff





• Attenuation

• Instrumentation

• Antenna probe

small antennas: r >> l fmin = 750 MHz

large antennas: r >> 2D²/l, D=10l fmin = 15 GHz

4m x 3m x 3m


maxmin fff





• Attenuation

• Instrumentation

• Antenna probe

ECCOSORB VHP-NRL: <-30 dB @ 3-4 GHz




maxmin fff





• Attenuation

• Instrumentation

• Antenna probe

ECCOSORB VHP-NRL: what about f >24 GHz


maxmin fff





• Attenuation

• Instrumentation

• Antenna probe

r = 4m, f=50 GHz, free-space propagation: -80 dB

cables’ attenuation: tens of dB


maxmin fff





• Attenuation

• Instrumentation

• Antenna probe

Cables and connectors limitations

frequency range and sensitivity of transmitter/receiver (e.g., VNA)


maxmin fff





• Attenuation

• Instrumentation

• Antenna probe

antenna horn in band X: fmin = 7 GHz


maxmin fff





• Attenuation

• Instrumentation

• Antenna probe

GHz 25GHz 3 f4m x 3m x 3m

Taking all the constraints into account:


x

y

z

a

g

bPhase center?


Antenna phase center



TX/RX antennas alignement problem

Solution: use laser pointers



TX/RX antennas alignement problem

Solution: exploit directly the radiation pattern



Example of measurement result (UNIPV near-field system)


Indoor far-field

Compact antenna test range (CATR)

Due to the double reflector system, the AUT is illuminated by a uniform plane wave in spite of the limited distance


Indoor far-field



AUT (RX)

Calibrated probe (TX)

AUT moving system

Hyperbolic reflector

Parabolic reflector

Indoor far-field



Indoor far-field



Indoor far-field



Indoor far-field



Indoor far-field



Indoor far-field



Calibrated probe (RX)

AUT (TX)

Indoor near-field

Planar scanning system


Indoor near-field



Indoor near-field



Indoor near-field

Cylindrical scanning system


AUT (TX)


Indoor near-field

Cylindrical scanning system


Indoor near-field

Spherical scanning system


Indoor near-field



Indoor near-field



AUT (TX)


Indoor near-field measurement details












2

2

y

x



2

2

z

a



aa 2;

2



zyxE ,,

0,, zyxE

0,,;0,, zyxEzyxE yx



2/

2/

2/

2/

0,,,b

b

a

a

ykxkjxyxx dxdyezyxEkkf yx

yx

jkr

ff kkfr

kejrE ,cos2

,,

yxx kkf , yxx kkf , yxx kkf , yxx kkf ,

yxx kkf ,



1

x

aM~ -30 dB

maxxk

x

222 kkk yx

ma

kx2

2n

zero-padding



1

x

aM

maxxk

x

ma

kx2

1 2102 mk

1max 10530sincossin mkkkk xx

cmx 3

mamkx 5.3 8.15.0 1

ma 2

64671

Mx

aM

Horn @ 10 GHz



1

x

aM

maxxk

x

ma

kx2

Horn @ 10 GHz409664 MxNM

hsT 640965




Probe radiation pattern correction

needed


Indoor (far-field/near-field)

+ Controlled environment (temperature, humidity, …)

+ No electromagnetic interferences + Accuracy– antenna dimension/frequency limitation

(far-field)– Frequency and dimension limitation– Strong post-processing (near-field)– Large number of samples (near-field)– Measurement of amplitude and phase

(near-field)

Outdoor vs indoor

Outdoor (far-field)

+ Simple measurement technique+ Limited post-processing– Large measurement field– High signal attenuation– Environmental/climate changes– Electromagnetic interferences


AUT (TX)

Sonda calibrata (RX)

Outdoor vs indoor


AUT (TX)

Sonda calibrata (RX)Errors due to the measurement equipment

• Instrumentation• Connection cables• Control/acquisition/processing software• Inaccurate placement of the probe

Errors due to the measurement setup• Multiple reflection in the measurement region• Undersampling and/or limited sampling surface• Non ideality of the probe

Possible source of errors

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Course on Microwave Measurements - unipv · Microwave Measurements 2014/15 Prof. Luca Perregrini...

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