I want to design a Power Amplifier using MRF6S21050L. Firstly, I simulated in the software ADS. To get the optimum Sourceimpedence and Loadimpedence, I used the tool-- LoadPull in ADS. However, the results of simulation in ADS are different from the datasheet. This question had puzzled me a long time. So I simulated some other LDMOS of NXP in ADS using Loadpull. I found the results are always different from the datasheet. Have you ever met this case? Could you give me some help to solve the problem?