Need Comments on Input Return loss for a Broadband PA

BMR said:

Hi Big Boss,

Ok So as said earlier the operating frequency range is 100-600MHz. I am using a push pull configuration So I designed a balun which ideally transforms 50-25ohms. So in this case the transformation ratio is approximately from 25 to 1.2 ohms(@470MHz from loadpull data) which is the transistor's input impedance.

So the figures above corresponds only to the input matching.


So usually a -10 dB or better than that return loss is considered as a good match, but since my BW is approximately 120% it's very difficult to maintain a -10 dB RL throughout So I decided just to match well at the highest Frequency and at lower frequencies since the amplifier has a good gain it won't matter much. That is my assumption. So does my assumption makes sense ?

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BigBoss said:

So your target is to match the input during whole bandwidth.
What kind of Balun-transofmer you have designed?? If you designed-for instance- coaxial Balun ( or equivalent Microstripline) transformer, it won't absolutely work because these kind of Baluns-transofmers have relatively narrow bandwidth.
Instead, you must try ferrite cored wideband transformer to match the input.
L-C Baluns won't also work because they work at single frequency too.
You may also coaxial-ferrite combination too.For more information seek amateur radio sites.They have very good practical examples.

Note : The input impedance of the transistor is 1.2 Ohm in according to Loadpull ?? It's really weird.I have never seen such low input impedance...

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