For an AR(2) time series, the triangular region below is the region for the parameters that ensures the time series is stationary. If the parameters lie in the region below the parabola the autocorrelation function is is a damped cosine wave. You can control the parameters by moving the red point around in the triangle. If you want to see a realization of this check yes and press the generate a realization button. The maximum value for n is 600.