Load stability circle and smith chart
Because you have 4 frequency points.Each one will show you which output impedance makes your amplifier stable or unstable..
To be more clear, see attached file. What do those 4 grey circles(small)+2 big circles from the center mean? which one is the real smith chart for reference in this picture?
../imgqa/eboard/Antenna/rf-4nxdcuntbzx.jpg
Stability Circles are outside of the Smith Chart that's why ADS used extended Smith Chart.
If a circle is outiside of the Smith Chart, there isn't any real impedance that makes your amplifier unstable.It means your amplifier unconditionally stable.
But make zoom and check other circles carefully.
Is there any option to turn off extended smith chart and see the single chart in ADS (other than using smithchart utility)?
