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VSWR on amplifier output

Question asked by PME75 on Apr 25, 2007
Latest reply on Apr 27, 2007 by PME75
Understanding VSWR measurments

Measuring VSWR with a network analyzer to an input of an amplifier is understood.  My specs also require measuring the VSWR of the output ports of the amplifier.  I have been a bit confused as to how the network analyzer can measure this properly.  My understanding is that an S11 vs an S22 is that the analyzer source swaps the source to each port.  So if port 2 is the amplifier output, how can the network analyzer put its source into the amplifier output and get any accurate result? 

If a 50 ohm termination is connected to the input of the amplifier (therefore, no signal going out) and the VSWR is measured into the output port, can this VSWR result be assumed to be the same as its output VSWR?  Someone with better understanding, please set me straight on this.