I have used an external attenuator of 30 dB
So, that means I have to remove the attenuator and measure again?With the 30dB attenuator at the output of you amplifier, you cannot measure amplifier S22.
If you calibrate without attentuator, you will measure almost no reflection from DUT because of the attenuator in between. And if you try to calibrate with attenuator in place, total reflection from cal standards will be attenuated by 2*30dB, which is too much for calibration to work.
So it is expected that S22 isn't meaningful using attenuator.
I also have used external DC block "Agilent 11742A Blocking Capacitor"Looks like there are small (0402 or so) blocking capacitors next to the connectors. Not so good in terms of impedance matching but at least capacitors.
It's not clear how the VNA has been calibrated considering the 30 dB attenuator. Volker already mentioned that it's almost impossible to get meaningful s22 measurement through attenuator, but how's the gain calibration?
How about S21?With the 30dB attenuator at the output of you amplifier, you cannot measure amplifier S22.
If you calibrate without attentuator, you will measure almost no reflection from DUT because of the attenuator in between. And if you try to calibrate with attenuator in place, total reflection from cal standards will be attenuated by 2*30dB, which is too much for calibration to work.
So it is expected that S22 isn't meaningful using attenuator.
The diagram shows the internal design of the VNA. The couplers are already there when using an industry standard VNA like E5071C.Agilent shows how to test DUT with Directional couplers and attenuators for testing all s parameters
Already checked the oscillation with signal generator and spectrum analyzer over wide frequency range and did not observe any oscillations.Attenuator is used to protect the VNA against input signals above the damage level (26 dBm for E5071C) which can be easily produced by the power amplifier output. It has to be included in two-port through calibration.
Measuring S22 (or even S11) of a power amplifier is somewhat risky. You need to double check before that the amplifier isn't oscillating.
The diagram shows the internal design of the VNA. The couplers are already there when using an industry standard VNA like E5071C.
@BigBoss Which type of screws are more suitable for RF?Your layout is not appropriate. Especially decoupling capacitors are not tied by screws. The screws which are used for Emitter/Source pins are anodized and they are definitely not proper for RF.
There is not via for GND connections.. etc etc..
So, please review your layout carefully..
I post here a good example..
View attachment 172530
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