I'm having a hard time understanding how formulas are derived from the diagram of a simple Doherty power amplifier circuit, as pictured below.
While I understand the concept behind load modulation and thus the necessity to introduce a λ/4 transmission line, I'm having trouble deriving the formulas shared by most of the literature I've explored and that I've pasted below. (Diagrams are in German, U stands for the voltage V.)
The main amplifier and the peak amplifier are represented as current sources I_H and respectively -jI_S. There's a load R_L, Z_H and Z_S are the impedances seen by the two current sources.
QUESTION 1) I understand that, looking from the node between resistance R_L and current source I_s into the transmission line, the high-ohmic impedance of current source I_H will look like a short circuit due to the length λ/4 of the transmission line, but I don't see how this implies that:
That is " the voltage at impedance R_L is only dependent on I_H."
How is this possible considering I_S is there, too? Also, is 'minus j' multiplied with I_H because the transmission line creates a phase shift in I_H?
QUESTION 2) How is following formula for the voltage at current source I_H defined? I've read that superposition is used here, so I guess one current source is observed in the circuit while the other is open-circuited and viceversa, then the two formulas are superposed. Yet, how was this done?
QUESTION 3) Lastly, I'm completely clueless as to why this is the impedance seen by current source I_S: