  An equivalent-multishell approach for the approximate calculation of the
characteristics of electromagnetic waves propagating in almost circular
(azimuthally symmetric), closely packed bundles of parallel, identical, and
metallic carbon nanotubes (CNTs) yields results in reasonably good agreement
with a many-body technique, for infinitely long bundles when the number of CNTs
is moderately high. The slow-wave coefficients for azimunthally symmetric
guided waves increase with the number of metallic CNTs in the bundle, tending
for thick bundles to unity, which is characteristic of macroscopic metallic
wires. The existence of an azimuthally nonsymmetric guided wave at low
frequencies in a bundle of a large number of finite-length CNTs stands in
contrast to the characteristics of guided-wave propagation in a single CNT. The
equivalent-multishell approach yields the polarizability scalar and the antenna
efficiency of a bundle of finite-length CNTs in the long-wavelength regime over
a wide frequency range spanning the terahertz and the near-infrared regimes.
Edge effects give rise to geometric resonances in such bundles.
  The antenna efficiency of a CNT bundle at the first resonance can exceed that
of a single CNT by four orders of magnitude, which is promising for the design
and development of CNT-bundle antennas and composite materials containing
CNT-bundles as inclusions.
