Can the noise figure of an amplifier be less than unity?

Can the noise figure of an amplifier be less than unity? as i made ADS simulation of noise, and obtain NF in values sometimes less than unity.. what's its units ? dB or ratio?

Also, how can it be less than one?!?!?!

Thanks in advance,
Ahmad,

The NF is expressed in dB..and it can be smaller than unity but it's always greater than zero.

well, why don't them in ADS display that it's in dB? Because noise figure is by defulat in dB? unlike noise factor, right?

anyway, thanks for help :D
Ahmad,