Regarding transistor RC Phase Shift Oscillator
Shahroze Shabab, here is my short advice:
I assume in the feedback path you are using the C-R highpass chain (3 elements), right?
You know that the required gain is -29 (in reality you need something more - perhaps 30..31).
Your problem is the influence of the finite input impedance r_in at the base. Hence, the &quot;last&quot; resistor in the chain is R||(r_in).
Why not simply remove the last ohmic resistor R ? In this case, the input resistance r_in alone could &quot;do the job&quot;. It should not be a big problem to make a good guess for h11=hie (input resistance at the base node) and you can use the voltage divider resistors to adjust the parallel combination to get the desired value of r_in.
Of course, a redesign of the whole C-R feedback chain would be necessary because ALL resistors should have the value of r_in.  I already have built such a circuit with good success.