A model is studied of sub harmonic generation in a ring cavity of arbitrary finesse. The model neglects the dynamics of the medium but incorporates propagation effects, i.e. spatial nonuniformity of the fields. Comparison with the predictions of the mean-field theory is made. Analysis of the cavity characteristics from the point of view of medium and cavity tuning curves, and existence of switching is made. A preliminary discussion on the propagation of pulses in a quadratically nonlinear cavity is also presented.