  The full ATLAS Run 2 data set with time-integrated luminosity of 139
fb$^{-1}$ in the diboson and dilepton channels is used to probe benchmark
models with extended gauge sectors: the $E_6$-motivated Grand Unification
models, the left-right symmetric $LR$ and the sequential standard model (EGM).
These all predict neutral $Z'$ vector bosons, decaying into lepton pairs,
$\ell\ell$, or into electroweak gauge boson pairs $WW$, where one $W$ in turn
decays semileptonically. 95% C.L. exclusion limits on the $Z'$ resonance
production cross section times branching ratio to electroweak gauge boson pairs
and to lepton pairs in the mass range of $\sim$ 1 - 6 TeV are converted to
constraints on the $Z$-$Z'$ mixing parameter and the heavy resonance mass. We
present exclusion regions on the parameter space of the $Z'$ which are
significantly extended compared to those obtained from the previous analyses
performed with LHC data collected at 7 and 8 TeV in Run 1 as well as at 13 TeV
in Run 2 at time-integrated luminosity of 36.1 fb$^{-1}$ and are the most
stringent bounds to date. Also presented, from a similar analysis of
electrically charged $W'$ bosons arising in the EGM, which can decay through
$W'\to WZ$ and $W'\to \ell\nu$, are limits on the $W$-$W'$ mixing parameter and
the charged $W'$ vector boson mass.
