It's impossible to make usual antennas to emit single-photon (Fock) states. What you'll emit are coherent states, which are more like a classical electrical wave than single-photon Fock states. If dimmed down to intensities with average photon numbers close (or even less than) one, the coherent state consists to a large amount of the vacuum state. With some small probability you may register one or (to even lesser probability) more photons in a statistical way. The probability distribution for the photon number in such a coherent state is the Poisson distribution,
$$P(N)=\frac{\lambda^N}{N!} \exp(-\lambda),$$
where ##\lambda## is both the average number ##\langle N \rangle=\lambda## of registered photons as well as its standard devition ##\langle N^2 \rangle -\langle N \rangle^2=\lambda##.