[Amps] antennas that are 1:1 vswr all over the band

[donii at sympatico.ca]

Gentlemen
A while back as I was listening to two rag chews on 80 they mentioned 
some kind of antenna that was extremely expensive and that could adjust 
its length according to the frequency transmitted. This must have been 
for 20 and higher. I don't know anymore as I wasn't really paying 
attention. Anybody know of this type of antenna? Could it be done?
Peter
VE2FAR