I am using Quantlib python to calibrate HW 1f model parameters from normal swaption vols quoted in the market (following the code in the cookbook - I fit both the mean-reversion & vol to market quotes)
I see the HW 1f vol is an average of the market implied vol term structure (for given expiry and different maturities for example) and fits very poorly to all the quotes.
What's a recommended approach/model to match the vol term structure observed from ATM swaption vols? Does Quantlib support any other advanced models?
Thanks, Sumit