# measure PA using Network Analyzer - RF Cafe Forums

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Post subject: measure PA using Network Analyzer

Unread postPosted: Fri Jun 17, 2005 7:29 am

I want to measure AM to AM and AM to PM using a Network Analyser. I am trying to use an external trigger on a 8753A Network analyser. It does not seem to be triggering¬/ Any ideas?

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Unread postPosted: Fri Jun 17, 2005 8:06 am

Hello,

The way to measure AM-AM and AM-PM curves is by doing Power Sweep. You have to be extremely careful with doing these measurements, becuase you rich to the P1dB and beyond. You have to use high power attenuator, at the output of the PA in order to both protect the VNA input and provide a good matching to the PA's output.

To do AM-AM, AM-PM measurements:

You have to know the output power you have to reach. Then subtract the gain of the PA from this value. This will give the maximal input power. Make a power sweep from a value of 10dB less to the value you found. For example if you found that the maximal input power is +5dBm, then the power sweep should be between -5dBm to +5dBm. A rule of thumb is to use an output attenuator with value equal or higher to the PA's gain.

Set the VNA's display to measure S21 phase and magnitude. The magnitude is the AM-AM curve and the Phase is the AM-PM curve.

During the measurement you can change the bias voltage level (Vgs) and see the effect of this on the curves.

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Unread postPosted: Fri Jun 24, 2005 11:31 am

thank you.

Posted  11/12/2012