Ron Wrote:
"What happens to cause radiation to begin?"

Ronold W.P. King wrote in "Transmission Lines, Antennas, and Wave
Guides, by King, Mimno, and Wing on page 224:
"Any closed loop of wire that is not confined to the near zone
(shielded) and that does not carry equal and opposite currents very
close together (adjacent and perfectly balanced though opposite)
radiates at least a fraction of the power supplied at its terminals."

Radiation is a phenomenon. Energy tries to spread out from where it is
to elsewhere. Unless it encounters barriers it just continues to spread.

Electromagnetic wave radiation is sustained by perpetual regeneration
from mutual stimulation. The electric wave contains all the energy for
an instant. The growth and decline of the electric field creates a
magnetic field which in turn creates an electric field and so on. These
fields can exchange their energies in a vacuum devoid of electrons or
electricity. They continue through the vacuum at the speed of light. The
waves go so far so fast that much energy escapes the attraction of its
source to recall it.

Terman says in his 1937 edition on page 700:
"A concentric transmission line radiates no energy under ordinary
conditions because the outer conductor acts as a substantially perfect
shield.

The power radiated from a non-resonant two-wire line:

Power radiated=160Isqd(pi a/lambda)sqd watts

I= line current

a/lambda= spacing in wavelengths""

In a resonant line, radiation is increased by about the ratio of peak
current to load current.

Best regards, Richard Harrison, KB5WZI