Abstract
We revisit the problem of realizing perfectly isotropic antennas based
on recent developments in nonlocal antenna theory. The key obstacle
against the existence of exactly isotropic antennas is traced back to
the hairy ball theorem in algebraic and differential topology. A path
blocking the applicability of this no-go theorem is to allow for
complementary longitudinal modes to coexist with matching transverse
modes in the antenna exterior region. Nonlocal antennas (radiators
embedded into nonlocal metamaterial exterior domains) are possible
future antenna technologies capable of dealing with both transverse and
longitudinal modes. It is rigorously demonstrated that the recently
proposed nonlocal Proca metamaterial (massive electromagnetism) leads to
small nonlocal dipole antennas with perfectly isotropic radiation
pattern. A tentative proposal for a possible experimental realization of
perfectly isotropic radiators in the future is briefly outlined.