  AR Scorpii is unique amongst known white dwarf binaries in showing powerful
pulsations extending to radio frequencies. Here we aim to investigate the
multi-frequency radio emission of AR Sco in detail, in order to constrain its
origin and emission mechanisms. We present interferometric radio frequency
imaging of AR Sco at 1.5, 5 and 9 GHz, analysing the total flux and
polarization behaviour of this source at high time resolution (10, 3 and 3 s),
across a full 3.6 hr orbital period in each band. We find strong modulation of
the radio flux on the orbital period and the orbital sideband of the white
dwarf's spin period (also known as the "beat" period). This indicates that,
like the optical flux, the radio flux arises predominantly from on or near the
inner surface of the M-dwarf companion star. The beat-phase pulsations of AR
Sco decrease in strength with decreasing frequency. They are strongest at 9 GHz
and at an orbital phase ~0.5. Unlike the optical emission from this source,
radio emission from AR Sco shows weak linear polarization but very strong
circular polarization, reaching ~30% at an orbital phase ~0.8. We infer the
probable existence of a non-relativistic cyclotron emission component, which
dominates at low radio frequencies. Given the required magnetic fields, this
also likely arises from on or near the M-dwarf.
