Abstract Submitted to the    NANOTUBE'04 Conference:

We investigate the electron transport in multiply-connected metallic carbon nanotubes within the Landauer-Büttiker formalism. Quasibound states are coupled to the incident $\pi^{*}$ states and give rise to energy levels of different widths depending on the coupling strength. In particular, donor-like states originated from heptagonal rings are found to give a very narrow level. Interference between broad and narrow levels produces Fano-type resonant backscattering as well as resonant tunneling. Over a significantly wide energy range, almost perfect suppression of the conduction of $\pi^{*}$ electrons occurs, which may be regarded as filtering of particular ($\pi^{*}$) electrons.