  Using our recently developed equivalent circuit model of radiative heat
transfer we analyze the far-field thermal emission from bodies of constrained
dimensions. We prove that the power radiated by a hypothetical metamaterial
emitter which is conjugate matched with all the harmonics of the emitted field
at a given wavelength can be infinitely higher than the power emitted by an
ideal black body of the same radius. However, for optically large bodies,
fulfilling the conjugate match conditions for higher-order harmonics is not a
trivial task, which effectively limits the far-field radiated power by the
well-known Planck law.
