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Mode-stirred chamber for measuring terminal antennas

Jan Carlsson, Per-Simon Kildal & Charlie Carlsson

Mode-stirred chamber for measuring terminal antennas

Antenna group at Chalmers

·Prof. Per-Simon Kildal ·Adj. Researcher Jan Carlsson from SP ·Ext. PhD student Kent Rosengren from Intenna ·...

Bluetest

·Owner Per-Simon Kildal ·Employee Charlie Carlsson

Mode-stirred chamber for measuring terminal antennas

Outline

· Background · The reverberation chamber

­ Reverberation chamber basics ­ What can be measured in a reverberation chamber? ­ Measurement of radiation efficiency

· Conclusions

Mode-stirred chamber for measuring terminal antennas

Measurement of terminal antennas

· Most terminal antennas, such as mobile phone ant., are used in a multipath environment. · It would be valuable also to measure the performance of antennas in such an environment.

Mode-stirred chamber for measuring terminal antennas

The reverberation chamber

· The reverberation, or mode-stirred, chamber creates a statistical multipath environment. · This makes it useful for measurement of small terminal antennas. · The reverberation chamber is well suited for measurement of the radiation efficiency.

Mode-stirred chamber for measuring terminal antennas

Some theory of the chamber

· The reverberation chamber is a resonant cavity · Supports some set of resonant modes

0

250M

500M

750M

1G

Frequency [Hz]

Mode-stirred chamber for measuring terminal antennas

Mode stirring

· The modes are excited with different amplitude · A change of geometry in chamber changes the excitation of modes · If the perturbation is big enough an independent field is created · This is referred to as `mode stirring' the field · Accuracy is determined by number of independent field samples

Mode-stirred chamber for measuring terminal antennas

What can be measured ?

Antenna setup Phone setup

Networ k analyzer

Power m eter

Base station

·Radiation efficiency ·Antenna impedance

·Total radiated power (TCP)

Mode-stirred chamber for measuring terminal antennas

Radiation efficiency measurement

· Make setup in chamber · Start measurement

­ Make frequency sweep ­ Collect data in computer ­ Move stirrer(s) to new position ­ Repeat for all positions ­ Process measured data

· Analyze measurement!

Networ k analyzer

Mode-stirred chamber for measuring terminal antennas

Measurement times

· In the setup used at the present, the dominant `time-consumer' is the network analyzer. · More modern analyzer will decrease times. · Also stirring takes time. · Examples of total measurement times are shown in the table.

Examples of measurement times

Positions 100 240 480 100* time ~8 min ~17 min ~33 min ~18 min

*=TCP measurement

Mode-stirred chamber for measuring terminal antennas

Reference case - chamber calibration

· In addition to the test case we also need to measure a reference case.

­ Reference case must have the same setup (loading) ­ We use a commercially available dipole as reference antenna ­ Same reference can be used for several test cases

Mode-stirred chamber for measuring terminal antennas

What can we get from a measurement?

· For the reference case we are interested in the chamber transmission function 2

Pref =

N

· Transmission for the AUT is extracted by 2

PAUT =

N

(1 - S )(1 - S )

2 2 11 22

S 21

(1 - S )(1 - S )

2 2 11 22

S 21

· This is the 0 dB reference level! (If we assume a lossless reference antenna.)

· Radiation efficiency for the AUT is then

erad = eohmic 1 - S 22, AUT eohmic = PAUT Pref

(

2

)

Mode-stirred chamber for measuring terminal antennas

Example of radiation efficiency measurement

0 Power level (dB) -5 -10 -15 -20 erad Pref PAUT

850

900 950 1000 Frequency (MHz)

Mode-stirred chamber for measuring terminal antennas

Validation case 1 ­ Dipole close to cylinder

r = 41 = 1.2 S/m

50 U 150 mm 300 mm

distance 10-100 mm

100 mm

Mode-stirred chamber for measuring terminal antennas

Comparison between FDTD-simulations and measurements

0 Radiatio n efficiency (dB) -1 -2 -3 -4 -5 -6 -7 1

D iamo nd: Measured in C halm ers chamb er Hexagram: Me asured in F O A cham be r C ircle: C alculated

f = 920 MHz cell size 2 mm

2 3 4 5 6 7 8 9 Distance fro m lo ssy dielectric (cm)

10

Mode-stirred chamber for measuring terminal antennas

Validation case 2 ­ Refl. Coeff. of dipole

Anechoic Chamber

Reverberation Chamber

Mode-stirred chamber for measuring terminal antennas

Dipole far away from cylinder

0

Reflection Coeffici ent (dB)

-10

-20

Measurement in anechoic chamber Simulation by WireMoM

Measurement in reverberation chamber

-30 600

700

800

900

1000

1100

1200

Frequency (MHz)

Mode-stirred chamber for measuring terminal antennas

Dipole 10 mm from cylinder surface

0

Reflection Coefficient (dB)

-10

-20

Me asurement in Anechoic cham ber Measurem ent in reverberation chamber

-30 600

700

800

900

1000

1100

1200

Frequency (MHz)

Mode-stirred chamber for measuring terminal antennas

Conclusions

· Good agreement between measurements in a reverberation chamber and other methods for validation cases · Measurements in reverberation chamber requires data processing · Possible to use small chambers at low frequencies (below 1 GHz) · Fast method for measuring radiation efficiency and TCP

Mode-stirred chamber for measuring terminal antennas

Information

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