GATE Electronics and Communications (EC) 2021 Solved Paper

The impedance matching network shown in the figure is to match a lossless line having characteristic impedance Z₀ = 50 Ω with a load impedance Z_L. A quarter-wave line having a characteristic impedance Z₁ = 75 Ω is connected to Z_L. Two stubs having characteristic impedance of 75 Ω each are connected to this quarter-wave line. One is a short-circuited (S.C.) stub of length 0.25 λ connected across PQ and the other one is an open-circuited (O.C.) stub of length 0.5 λ connected across RS.
  
The impedance matching is achieved when the real part of Z_L is