In this forum I've often read that EM radiation does not consist of photons (ie be emitted from accelerated electrons in an antenna rod) and that photons are only excitations of an already existing EM field. How can one connect this with the Standard Model of physics, where photons are particles? Would a different model of quantum theories negate the existence of photons?
The SM (standard model) is in comparison to the QFT (Quantum field theory) as newtonian physics is to special relativity. It is still applicapble, but contains more information. So when you ask if it would negate the existance of photons, the answer is no. It is just written in a different format. For all purposes within the standard model, photons still exist, as they do in QFT, but there they simply exist as excitations:
For a general overview of QFT see: https://en.wikipedia.org/wiki/Quantum_field_theory