Short-duration, high brightness temperature radio transients such as pulsar emission and fast radio bursts require the coherent radiation of particles. The antenna class of coherent radiation models require a large number of charged particles radiating in phase, therefore the particles must be spatially confined and have well-aligned velocities. We look at the magnetic field induced by the currents associated with coherently emitting accelerated particles and consider the interaction between the radiating particles and the induced magnetic field. We find a maximum luminosity of coherent curvature emission in sub-critical magnetic fields that is in agreement with maximum observed luminosity from giant pulses, furthering the hypothesis that FRBs originate from magnetic fields above 10^(14) G. Using giant pulses from the Crab Pulsar as an example, we constrain the emission parameters and origin to within 60km of the pulsar surface, and suggest the most extreme nanoshots observed must originate very close to the pulsar surface. In agreement with recent observations, we also predict simultaneous X-ray emission due to small-scale incoherent particle gyration due to the induced field.
