Andrey GleenerAndrey Gleener R&D Services Ltd.a8421@intergate.ca

IEEE Joint Communications Chapter - Vancouver

January 12, 2009

Antenna Efficiency Measurements

Pin - Power applied to Antenna Terminals

Prefl

Prad

Pacc

Pdiss

Pin

Prefl - Power reflected from Antenna Terminals

Pacc - Power accepted by Antenna

Pdiss - Power dissipated in Antenna structure

Prad - Power radiated

rad - Radiated Efficiency

tot - Total Efficiencyrad =Prad

Pacc

tot =Prad

Pin

= (1- |S11|2)rad

Antenna Efficiency

• Antenna Pattern Integration method

• Radiometric method

• Wheeler Cap method

Methods of Efficiency Measurements

Antenna Pattern Integration Method

Antenna Pattern Integration Method is calculation of Antenna efficiency according to it’sdefining formula

where Prad is derived by integrating 3D Antenna Pattern measured in anechoic chamber.

tot =Prad

Pin

Prad=

4R2

2Gr

2

0 0

{pp(,) + px(,)}sin d d

tot =Prad

Pin

Radiometric Method

Radiometric method – measurements of the Noise Power generated by Antenna itself.

Noise measured from sources with two different temperatures one of which (Tc) is very low and another (Tw) is close to ambient.

TcTw

rad =

Pw

Pcref

- 1Pw

Pc

( )ref

Pw

Pcref

- 1Pw

Pc

( )ref

Radiometric method is practical only for high-directivity antennas

Wheeler Cap Method is calculation of Antenna efficiency based on measurement of it’s impedance in two conditions: Antenna in open space and Antenna enclosed in Cavity with reflective walls.

Wheeler Cap Method

Wheeler Cap Method does not require anechoic chamber, clear sky or reference Antenna. It does require a Cap though.

David M. Pozar and Barry Kaufman, "Comparison of Three Methods for the Measurement of Printed Antenna Efficiency" IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 36, NO. 1, JANUARY 1988

Accuracy of Efficiency Measurements

Method AccuracyAntenna Pattern Integration Method 20%Radiometric Method 12%Wheeler Cap Method 2%

H. A. Wheeler, "The radiansphere around a small antenna," Proc. IRE, S. 1325-1331, Aug. 1959.

Wheeler Cup Method

Harold Wheeler

Ronald Johnston and John McRory

tot = |S21|2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-1 -0.5 0 0.5 1

Smax

Smin

S11fs

S11wg

"An Improved Small Antenna Radiation-EfficiencyMeasurement Method " IEEE Antennas and Propagation Magazine, Vol. 40, No. 5, October 1998

tot =2

(Smax)-1+(Smin)-1

waveguide

Antenna under test

feed port

slidingshort

[S] Z0

Antenna is two-port network and in free space is terminated with matched load. Inside the waveguide the terminating impedance is short circuit.

S21= f(S11fs ; S11wg)

O. Litschke, M. Geissler, D. Heberling, P. Waldow, I. Wolff "Adoption of the Wheeler-Cap method for measuring the efficiency of mobile handset antennas”c 2003

tot =2

(Smax)-1+(Smin)-1

(IMST GmbH)

[S] Zcap ; lcap

Antenna is two-port network and inside the cap it is terminated with impedance of the cap (which is short). Generalized transmission line exists between the short and the Antenna.

S11fs

S11cap

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-1 -0.5 0 0.5 1

Smax

Smin

Patch Antenna in Wheeler Cap

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

-1.00 -0.80 -0.60 -0.40 -0.20 0.00 0.20 0.40 0.60 0.80 1.00

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

-1.00 -0.80 -0.60 -0.40 -0.20 0.00 0.20 0.40 0.60 0.80 1.00

Plots of S11 extracted from Network AnalyzerOn both Plots:Blue line - antenna in Free SpacePink line - antenna inside Wheeler Cap

Patch Antenna with Air Substrate Patch Antenna with Plastic Substrate

Efficiency of Patch Antenna with Air Substrate compared with Patch Antenna with Plastic Substrate.

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

2400 2410 2420 2430 2440 2450 2460 2470 2480

Frequency (MHz)

Eff

icie

nc

y

Air Substrate

Plastic Substrate

Patterns of Patch Antenna with Air Substrate compared with Patch Antenna with Plastic Substrate.

-61.0

-51.0

-41.0

-31.00

5 10 15 2025

3035

4045

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

125

130

135140

145150

155160165170175

180185190195200

205210

215220

225

230

235

240

245

250

255

260

265

270

275

280

285

290

295

300

305

310

315320

325330

335340 345 350 355

Air Substrate

Plastic Substrate