B Why does charge oscillate in an electric dipole antenna?

[versine]

Picture: Energy source => LR Oscillator => Transformer => Transmission line => Electric dipole antenna => traveling wave
Why would the charge even oscillate in the antenna as opposed to building up in the antenna? The transmission line + antenna is not a closed circuit right?

 

[nsaspook]

What does charge building up mean here?

Review this to see how charge moves in response to the applied RF energy.


"Open circuit" used in the typical circuit theory description can't be used with antenna circuits. You will need to refine your understanding of current and voltage. The antenna is a transducer between free EM radiation and Kirchhoff circuit rules that require a bit of deeper study to see that antennas are part of closed circuits.

 

[tech99]

The crux of your problem seems to be that the dipole is an open circuit. However, it is not, because the capacitance between the arms completes the circuit. When a radio-frequency alternating current flows in this circuit, the electrons in the dipole rods are caused to accelerate back an forth at the frequency of the transmitter. When charges accelerate they radiate. The radiated energy travels away from the antenna as an EM traveling wave.
Energy is also stored in the system because the dipole is resonant, but about 10% is radiated each cycle.

 

[Baluncore]

Why would the charge even oscillate in the antenna as opposed to building up in the antenna?

A λ/2 dipole can be modeled as a resonator, a transmission line with reflection from the open circuit at both ends.
As the dipole is driven with energy through the feedline, the amplitude of the wave on the dipole increases, until the rate of radiation from the dipole to space is equal to the rate energy is being delivered through the feedline.