We present predictions for the radio pulses emitted by extensive air showers using ZHAireS , an AIRES-based Monte Carlo code that takes into account the full complexity of ultra-high energy cosmic-ray induced shower development in the atmosphere , and allows the calculation of the electric field in both the time and frequency domains .
We do not presuppose any emission mechanism and our results are compatible with a superposition of geomagnetic and charge excess radio emission effects .
We investigate the polarization of the electric field as well as the effects of the refractive index n and shower geometry on the radio pulses .
We show that geometry , coupled to the relativistic effects that appear when using a realistic refractive index n > 1 , play a prominent role on the radio emission of air showers .