Further to antenna bandwidth.

The concept of Q = Inductive reactance / loss resistance applies equally to
coil plus capacitor tuned circuits and to antennas.

Because capacitance loss is negligible, antenna Q depends only on loss
resistance of the wire inductance. Loss resistance = uniformly distributed
radiation resistance + wire resistance. Uniformly distributed radiation
resistance for a half-wave dipole is exactly twice the centre-fed value,
ie., approx 140 ohms.

Formula for the inductance of a straight length of wire can be found in
Terman and many other places. It is then a simple matter to calculate
dipole Q = inductive reactance / loss resistance.

Bandwidth can be described in terms of the 3dB points or in terms of the SWR
= X points.

But, as stated earlier, what matters is radiating system bandwidth, antenna
+ transmission line + tuner. And doubling antenna wire diameter has no
noticeable effect on operating bandwidth. Increasing wire diameter by 100
times may double bandwidth but is not worth the trouble and expense for only
one band.

Discussion of antenna bandwidth at HF, always in non-numerical terms, is an
overated topic.
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Reg, G4FGQ