  Here we report on the total-intensity 610 MHz GMRT observations of the
peculiar hybrid blazar SBS B1646+499, which merges the properties of BL
Lacertae objects and flat-spectrum radio quasars. The complex radio structure
of SBS B1646+499, emerging from the archival radio data and our new GMRT
observations, consists of the Mpc-scale, elongated halo, the unilateral
kpc-scale jet, and the nuclear jet extending up to 20pc from the compact core.
The giant halo is characterized by a steep radio spectrum, indicative of the
advanced ageing of the electron population within the lobes. For the
large-scale jet, we detected a spectral gradient along and across the outflow,
and in particular spectral flattening of the radio continuum toward the jet
edges, suggestive of the spine--boundary shear layer morphology. The nuclear
jet displays superluminal knots emerging from the self-absorbed and variable
radio core. We interpret all these findings in the framework of the model of an
episodic jet activity with a precessing jet axis.
