  The SLAC T-510 experiment was designed to compare controlled laboratory
measurements of radio emission of particle showers to predictions using
particle-level simulations, which are relied upon in ultra-high-energy
cosmic-ray air shower detection. Established formalisms for the simulation of
radio emission physics, the "endpoint" formalism and the "ZHS" formalism, lead
to results which can be explained by a superposition of magnetically induced
transverse current radiation and charge-excess radiation due to the Askaryan
effect. Here, we present the results of Geant4 simulations for the SLAC T-510
experiment, taking into account the details of the experimental setup (beam
energy, target geometry and material, magnetic field configuration, and
refraction effects) and their comparison to measured data with respect to e.g.
signal polarisation, linearity with magnetic field, and angular distribution.
We find that the microscopic calculations reproduce the measurements within
uncertainties and describe the data well.
