How does a dipole antenna work

A changing magnetic field will induce an emf in a wire (it needn't be a loop).

 

There are many ways of interpreting that line, please specify which interpretation is the correct one.

 

Well the direction of the electric field is at a right angle to the direction the EM wave would be going. So parallel to that would be under or over the direction of the electric field? I'm pretty sure there's more ways of interpreting that but is that the correct one? I'm not very good at reading in general, but I want to make sure, thanks.

 

what light ??

we are talking about radio wave E-M field


Dave

 

When I wrote light I meant an EM wave, some animals may be able to see radio waves so I included them as light. I changed my previous post, it's more clear now that way.

 

try the ARRL Radio Handbook
it gives a very good background to radio transmission and reception including antenna theory


cheers
Dave

 

So where exactly is parallel? Nevermind about the over and under thing.

 

Thanks!

 

So if the antenna is vertical and the electric field is vertical and the photon moves by the antenna but is a bit too far left to hit it directly, could the magnetic field induce current in the antenna?

 

Even with the antenna and the electric field being at 90 degrees to each other there will still be some signal induced into the antenna .... just not very efficiently

In the field, in pratical situations, we see a 25 to 30 dB difference in signal strength when the polarisation is out by 90 deg

Dave

 

If the polarization of the signal is vertical and the photon meets the vertical antenna straight on, will that generate the most current? I hope this has to do with dipole antennas.

 

A dipole is when the two conductor feed line is attached at the center between two separate long elements. This configuration is usually horizontal. but may be vertical, sometimes an inverted "V" shape... etc.
A true "vertical" antennae is distinguished by being configured vertically but with a single element, the feed line attaching one lead to the vertical element and the other to ground (usually a ground plane of radiating rods on the ground or similar, lots of designs).

The noteworthy behavior of a dipole is the relationship between current and voltage at different parts of the antennae... it alternates from having high voltage and low current at the distal ends of the elements while having low voltage and high current at the center, to having low voltage and high current at the ends and high voltage and low current at the center.

That is the basic mechanism in principle for both sending and receiving... how that relates to the emission and reception of EM is more complicated - ARRL books have great info and practical "theory", but may not get down to the level of a suitable "physics" answer.

 

Photons are not like little bullets and they don't "meet and antenna" in the conventional sense. It is really not helpful to look at it this way. How could you even start to consider how this single photon (dimensions / extent totally unspecified) will interact with a piece of metal, which consists of a distribution of charges all over it? Stick to waves if you want to understand most non-QM phenomena. There is nothing wrong with ( you are not making any compromises) using the wave approach.