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April 2012 HF Technology, Eindhoven, April 2012 1
High Current RF-testing
ing. R.O. de MeijerAR Benelux BV
Customer’s target
• Testing of RF-current breakdown levels for currents > 50A rms
• Improvement of quality and reliability of the product.
• Not all the customer’s suppliers specify these breakdowns.
• Perform the testing in-house, as part of the design cycle and QA program
April 2012 HF Technology, Eindhoven, April 2012 2
Customer’s target (cntd)
• Various components:
– Connects– Capacitors– PIN diode switches
• Preferably making use of the customer’s amplifiers– Pulse with 30 kW peak power @ 3% duty– 63 and 127 MHz
April 2012 HF Technology, Eindhoven, April 2012 3
Problem definition
• RF amplifiers have 50Ω output impedance
• Because 50Ω is not low, the maximum deliverable current will not be high
• In case of Pout = 30 kWatt into 50 Ohm
April 2012 HF Technology, Eindhoven, April 2012 4
AIrms 5.2450
30000
Enlarging the current
• With a constant power level the only option is lowring the impedance in the test cicrcuit.
• Transformation from 50Ω to 5Ω
• The implication for the current now flowing through 5Ω is
• This complies to the customer’s spcification
April 2012 HF Technology, Eindhoven, April 2012 5
AIrms 775
30000
Impedance transformation
• With 30kW pulse and 3% duty cycle Pavg ~ 1kW
• Low-loss transformation is a must.
• Loss less transformation with a ¼λ coaxial transformer
• Two operational frequencies– 63 MHz λ = 4m75– 127 MHz λ = 2m36
April 2012 HF Technology, Eindhoven, April 2012 6
50Ω 5ΩZtr30kW
LOAD
L= λ/4
¼ λ coaxial transformer
• Coaxial cables with this characteristic impedance is not easily available
• The impedance of a coaxial line
• D = diameter outer conducter • d = diameter inner conducter
• εr = rel. dielectrical constant
April 2012 HF Technology, Eindhoven, April 2012 7
d
D
r10log
138
81.15550xZtr
Creation of the ¼λ coaxial transformer
• Brass pipes with 17 and 13 mm diameter
• Make up a Z0 of 16Ω
• Two models, 63 MHz and 127 MHz
April 2012 HF Technology, Eindhoven, April 2012 8
127 MHz63 MHz
The transformed impedance on the Smith-Chart
April 2012 HF Technology, Eindhoven, April 2012 9
5Ω 50Ω
Test set-up
April 2012 HF Technology, Eindhoven, April 2012 10
50Ω 5Ω15.8ΩEUT BOX
5Ω1 kW
L
1 kWatt 5Ω load
April 2012 HF Technology, Eindhoven, April 2012 11
The 5Ω point
20 x 100Ω parallel
Unwanted effetcs in the set-up
• Electrical lengths inside the EUT box• Zload = R + jωL
• The ¼ λ transformator will not supply 50Ω to the amplifier.
April 2012 HF Technology, Eindhoven, April 2012 12
Solution (theoretical)
April 2012 HF Technology, Eindhoven, April 2012 13
The solution (practical)
April 2012 HF Technology, Eindhoven, April 2012 14
2 x 50Ω stub-tuner
Stub-tuner detail
Conclusion
• All transmission lines have air-dielectricum, with de εr = 1
• No dielectrical losses.
• With the ¼ golf transmission line and the supporting stub tuners all paracitic effects in the EUT box are eliminated.
• The amplifier ‘sees’ under all conditions 50 Ω
• Full power available for the ‘destructive’ test
April 2012 HF Technology, Eindhoven, April 2012 15
April 2012 HF Technology, Eindhoven, April 2012 16
AR Benelux B.V.Frankrijklaan 72391 PX HAZERSWOUDE-DORP
Telefoon : +31 (0)172 423000Web-site : www.arbenelux.com
E-mail : [email protected]
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