  We propose the implementation of a Josephson radiation comb generator (JRCG)
based on an extended Josephson junction subject to a time dependent magnetic
field. The junction critical current shows known diffraction patterns and
determines the position of the critical nodes when it vanishes. When the
magnetic flux passes through one of such critical nodes, the superconducting
phase must undergo a $\pi$-jump to minimize the Josephson energy.
Correspondingly a voltage pulse is generated at the extremes of the junction.
Under periodic driving this allows us to produce a comb-like voltage pulses
sequence. In the frequency domain it is possible to generate up to hundreds of
harmonics of the fundamental driving frequency, thus mimicking the frequency
comb used in optics and metrology. We discuss several implementations through a
rectangular, cylindrical and annular junction geometries, allowing us to
generate different radiation spectra and to produce an output power up to
$10$~pW at $50$~GHz for a driving frequency of $100$~MHz.
