  The radiation principle of travelling-wave type phase-reversal antennas is
explained in details, unveiling the presence of magnetic-dipole radiation in
addition to well-known electric dipole radiation. It is point out that such
magnetic dipole radiation is specific to the case of traveling-wave
phase-reversal antennas whereas only electric-dipole radiation exists in
resonant-type phase-reversal antennas. It is shown that a phase-reversal
travelling-wave antenna alternately operates as an array of magnetic dipoles
and an array of electric-dipoles during a time-harmonic period. This radiation
mechanism is confirmed through both full-wave and experimental results.
