  Gamma-ray detected radio-loud narrow-line Seyfert 1 (g-NLS1) galaxies
constitute a small but interesting sample of the gamma-ray loud AGN. The
radio-loudest g-NLS1 known, PKS 2004-447, is located in the southern hemisphere
and is monitored in the radio regime by the multiwavelength monitoring program
TANAMI. We aim for the first detailed study of the radio morphology and
long-term radio spectral evolution of PKS 2004-447, which are essential to
understand the diversity of the radio properties of g-NLS1s. The TANAMI VLBI
monitoring program uses the Australian Long Baseline Array (LBA) and telescopes
in Antarctica, Chile, New Zealand, and South Africa to monitor the jets of
radio-loud active galaxies in the southern hemisphere. Lower resolution radio
flux density measurements at multiple radio frequencies over four years of
observations were obtained with the Australia Telescope Compact Array (ATCA).
The TANAMI VLBI image at 8.4 GHz shows an extended one-sided jet with a
dominant compact VLBI core. Its brightness temperature is consistent with
equipartition, but it is an order of magnitude below other g-NLS1s with the
sample value varying over two orders of magnitude. We find a compact morphology
with a projected large-scale size <11 kpc and a persistent steep radio spectrum
with moderate flux-density variability. PKS 2004-447 appears to be a unique
member of the g-NLS1 sample. It exhibits blazar-like features, such as a flat
featureless X-ray spectrum and a core dominated, one-sided parsec-scale jet
with indications for relativistic beaming. However, the data also reveal
properties atypical for blazars, such as a radio spectrum and large-scale size
consistent with Compact-Steep-Spectrum (CSS) objects, which are usually
associated with young radio sources. These characteristics are unique among all
g-NLS1s and extremely rare among gamma-ray loud AGN.
