please help.

Calculate b4 as a function of a1 when the loads on ports 2 and 3 vary between two values 21 and 22, producing identical reflection coefficients on those ports that you can call r; with j = 1,2. The four-port network is a quadrature coupler whose matrix [S] is given by: 0 1 S: 01' _1j0 .510 01 1 0 01' 1'0