Dipole antennas & Conductivity

[oddwolf]

Hello!

I have two quick (hopefully) questions about dipole antennas and conductivity.

1) Two dipole antennas are placed at the points (λ/4,0,0) & (-λ/4,0,0) where λ is the wavelength of the emitted radiation. The dipole moments are:

p1 = p_ω *e^(-ωt)
p2 = p_ω *e^(-(ωt-α))

where p_ω is constant, ω is the angular frequency and α is the phase-shift between the two antennas.

And now for the question, if α = 0, do the two antennas amplify or thwart the radiation along the y-axis? the x-axis? How do you rotate the radiation zone 90 degrees?

2)

Suppose you have some sort of conductive body with a charge density of ρ (free particles) at t = 0. qualitatively how do the particles redistribute on the body, and if there's a net charge on the body, where do the charged particles go and what happens? Also what happens with the charge distribution inside the body for t > 0?


My thoughts:

1)

On the first two questions I have a feeling that it amplifies along the y-axis and thwarts the radiaton along the x-axis, why though I am not sure. As for the last question, I suspect you just change the distance between the antennas, but I'd love some explanation on how to.

2)

Pretty lost on this one, would reallui appreciate som help.



Thanks!

 

[jbsteele]

For the first question, it is correct that the two dipole antennas will amplify the radiation along the y-axis and thwart the radiation along the x-axis if α = 0. To rotate the radiation zone 90 degrees, you can simply change the orientation of the antennas so that the dipole moments are pointing in different directions. For example, you could rotate one antenna 90 degrees around the y-axis and keep the other in the original position. For the second question, the particles with charge density ρ will redistribute on the body according to the laws of electrostatics. The particles will move toward regions of lower electrostatic potential energy, and they will be repelled from regions of higher electrostatic potential energy. If there is a net charge on the body, the charged particles will move to the area of highest potential energy. For t > 0, the charge distribution will depend on the nature of the body and the forces acting on it.