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Andrey GleenerAndrey Gleener R&D Services [email protected]
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