Choice of capacitors to Impedance Matching Network in RF PA?

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berger.h

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I create 150W PA for fixed frequency undrer 20MHz. On output is LC Impedance Matching Network and I need advice on choosing the type of capacitors.
L I create on iron powder size T130 induction around hundreds nH.
C is around 900pF and my choice is use 7*150pF parallel. Voltage rating min 4xDC >=200V
In the prototype I used silver mica, but they are expensive and I would like to avoid them
My second choice is SMD ceramic NPO.
In Mouser.com I make filter
150pF, U >200V, COG, precisoon =< 5% , in stoct and mouser have 44 psc
if add as condition RF Microwave/High Q will remain 5psc in real only
this
and this
Is it a good choice or do you recommend something else?
 

You don't need RF/Microwave type Capacitor. C0G with High Voltage type is enough for 20 MHz
 

Thank you.
The problem is if I want more than 5% accuracy, It is 2% other than RF/Microwave hi Q they are not on mouser.com in offer.

And so I still prefer 251R15S151GV4E
According to datasheet on frequency under 20MHz
250V, 0803, 2% accuracy
ESR around 30mOhm,
Q high than 2000
max current on 13MHz around 2A
So, I'd give priority to something in size 1210, because I would have assumed a higher current and less stress in the Dielectric, but this is not really offered by the mouser.
Maybe in the 5% class, but I don't know if it would be inaccurate.
 

Don't be hung up on tolerances, you will need a tuning at final stage.It's essential that the Capacitor must be robust against high Currents and Voltages and of of course reliable.
If this system will work in a harsh environment with high temperature, the reliability has strong priority.
 

The possibility of using 5% capacitors and adding a position for another fine tuning capacitor I also considered.
Yes, I also think current is the key, so I use 6C in parallel.
the problem is, for most conventional SMD ceramics, manufacturers do not provide max current and they are also silent about reliability or longevity :lol:
C the selected type has an operating temperature of up to 125C, my PA should turn off automatically at 85C
 

I try compare actually available NPO SMD RF capacitors in size 0805 and 1111

Name Size V ESR Q I RMS
251R15S151GV4E 0805 250V 40mOhm 2500 1,5A 100pF at 13MHz
VJ1111D151GXLQ 1111 630V 60mOhm 2100 12A 100pF at 20MHz

As expected , larger size improved cooling and increased max current 1,5A vs 12A, Q and ESR on the other hand, better for smaller 0805, probably due to lower voltage rating and lower inductance of smaller 0805.
Price 1111 is higher (lower quantity discount)
1111 = 8x higher current , but higher ESR and higher voltage resistance
0805 = lower ESR, higher Q lower price and size

I have it compared, but I still do not know whether to use 1111 or 0805 :laugh:
 

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