How to generate power spectra of AR-1 process in matlab?

Question

I have a time series x1 as 3600x1 double. I need to fit AR-1 spectra on the power spectral density of x1. Well, I am not an expert and this is the first time I am studying time series.

If AR-1 process is given as: X(t)=alpha1*X(t-1)+z(t) So far I have calculated variance of time series, variance of noise (z(t)) and the value of alpha1. However, I am unable to find a function in Matlab which can plot spectra of AR-1.

I tried ar(),pyulear(),psd(),freqz,lpc etc functions. What am I doing wrong?

Thanks for the help.

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smoothened plot - AR-1 process spectra , skewed plot- spectra of time series