Re: Matching LDMOS device


Greg - ZL3IX
 

I'm not a PA specialist, but have designed one or two in the distant past. I believe that you need to use the impedance characteristics under drive at a typical power level, and these are not usually the same as would be the case under small signal conditions, ie when measured with a VNA. Making impedance measurements under drive is not a simple matter, and you may do well to take the manufacturer's data, here https://www.nxp.com/docs/en/data-sheet/MRF184.pdf.  Admittedly it only goes to 1 GHz, so you would need to attempt extrapolation up to 1.3 GHz. Even at 1 GHz the plot looks like around 1 ohm for Zin, which is way different from the 13 ohms you measured on your VNA.

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