can someone please explain de-diplexor circuit

Attachment 53204

Hello can anyone please explain what the RED quarter wave transformer does in this circuit and how it helps in passing

only RF rather than DC, an explanation using quarter wave transformer Zo=sqrt(Zin*Zout) would be greatly appreciated.

I know the black quarter wave transformer blocks RF because on the DC end is a grounded capacitor hence Zin = ∞ as Zout=0 I dont understand the function of R and C on the Rfout end. Please any help would be appreciated

In my opinion, the function of the "red" quarter wave transformer is impedance transformation. C is required to block the DC.

If the Z0 of the "red" line is above the reference impedance, and less then quarter wave length, the combination of "black" and "red"+C sections may be part of a 2nd order band pass filter (with good return loss). The "red" + C section behaves as a series resonant circuit (seen from RF + DC). Together with the parallel circuit behavior of the "black" line, a 2nd order band pass filter appears.