I have to design an active filter of order 2 low-pass rauch bessel structure. i found the circuit online under this name : MFB Complex Pole-Pair Section or Infinite-impulse, multiple feedback low pass filter. I have f cut=15Hz C1=50 pF. I need to find R1=R2=R3=R and C2. I was given the bessel coefficients a1=1.340, b1=0.490,a2=0.774, b2=0.389