I think you should read this wiki article: -

Basically, because a sinewave can be broken in half in the time axis, you get a full internal coherent reflection with the forward applied voltage when you match then antenna dipole length to the electrical half \$\lambda\$ of the applied voltage. This also works at a quarter \$\lambda\$ and multiples thereof.

At other in-between frequencies you get asymmetrical reflections that have the effect of producing capacitive or inductive impedances as seen by the source voltage and, are not as effective as a means of emitting radio power. I'm not saying they don't work, just that they are not as effective.

It's exactly the same theory as the tube of a church organ. They are resonantly tuned in length to produce the correct fundamental pitch when excited with air. They can be open-ended or closed: -

Picture from here.

I think you should read this wiki article: -

Basically, because a sinewave can be broken in half in the time axis, you get a full internal coherent reflection with the forward applied voltage when you match the antenna length to the electrical half \$\lambda\$ of the applied voltage. This also works at a quarter \$\lambda\$ and multiples thereof (just like the pipe of an organ). These are called standing waves.

At other in-between frequencies you get asymmetrical reflections that have the effect of producing capacitive or inductive impedances as seen by the source voltage and, are not as effective as a means of emitting radio power. I'm not saying they don't work, just that they are not as effective.

It's exactly the same theory as the tube of a church organ. They are resonantly tuned in length to produce the correct fundamental pitch when excited with air. They can be open-ended or closed: -

Standing wave pictures from here.