  The linear conductance spectrum of a metallic graphene junction formed by
interconnecting two gapless graphene nanoribbons is calculated. A strong
conductance suppression appears in the vicinity of the Dirac point. We found
that such a conductance suppression arises from the antiresonance effect
associated with the edge state localized at the zigzag-edged shoulder of the
junction. The conductance valley due to the antiresonance is rather robust in
the presence of the impurity and vacancy scattering. And the center of the
conductance valley can be readily tuned by an electric field exerted on the
wider nanoribbon.
