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April 2012 HF Technology, Eindhoven, April 2012 1
High Current RF-testing
ing. R.O. de MeijerAR Benelux BV
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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
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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
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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
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AIrms 5.2450
30000
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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
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AIrms 775
30000
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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
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50Ω 5ΩZtr30kW
LOAD
L= λ/4
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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
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d
D
r10log
138
81.15550xZtr
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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
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127 MHz63 MHz
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The transformed impedance on the Smith-Chart
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5Ω 50Ω
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Test set-up
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50Ω 5Ω15.8ΩEUT BOX
5Ω1 kW
L
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1 kWatt 5Ω load
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The 5Ω point
20 x 100Ω parallel
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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.
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Solution (theoretical)
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The solution (practical)
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2 x 50Ω stub-tuner
Stub-tuner detail
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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
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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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