# Closing the loop and creating the current in antennas

I remember Feynman explained that raid waves are emitted by accelerated charged particles. So, the only the things that antenna transmitters do is just up-down oscillation of the current simulate this circuit – Schematic created using CircuitLab

Since this wire vertical, oscillation should create the the photons flying away horizontally in all directions. But how do you close the loop? The wire cannot be infinitely long. Does it mean that you must emit the same amount of radiation in perpendicular direction? Probably it is good that you produce the bi-polarized signal, which is easier to detect. You have to wire the backward vertical current at the right distance (half wavelength) so that it is coherent and does not interfere negatively with first one at large distances. But donesn't its radiation affect the current in the first wire (and vice versa)? Can you ever have an electron oscillation in the wire without the loop? Since most antennas that I have seen are unclosed wires, I believe that you can. But, how is that ever possible?

• There's stray capacitance between the antenna and the ground, and between the two ends of the antenna (among other places where there's stray capacitance). – user253751 Oct 2 '16 at 21:33
• RF Current flows to and fro in a dipole antenna. The current amplitude is zero at the ends since there is nowhere for it to flow to. Voltage amplitude is maximum at the ends as this is where the charge carriers accumulate. – Chu Oct 2 '16 at 22:05
• Your question is a little bit difficult to understand due to terminology which is not standard. But you seem to have a real intellectual curiosity about electromagnetic waves. The answer to all your questions can be found by studying maxwell's equations and how they apply to antennas. Single wire antennas rely on having a ground plane of some sort. Due to boundary conditions, the ground plane creates a reflection of the single wire. It is like a virtual dipole. Current can flow in an open circuit antenna because of transmission line effects. – mkeith Oct 3 '16 at 15:43
• en.wikipedia.org/wiki/Distributed_element_model – mkeith Oct 3 '16 at 15:46

See image below for graphic on current flow in a dipole antenna: Transmission is very similar, the current creates the electromagnetic wave rather than vice versa. The video is the same for both.

The point is, the antenna does not need to be a closed loop in order to operate, because the current does not flow in a particular direction for anything other than a very short time.

• I am fine with short answers and this one is certainly illuminating. But, I asked about oscillation GENERATION. Do you apply the voltage generator in place of R which moves the electrons towards the antenna endpoints? Should the oscillation speed be proportional to the electron speed in conductor then or to the field propagation speed? – Little Alien Oct 3 '16 at 6:44
• Electron speed does not matter. C = lambda * f. C is propagation speed. Lambda is wavelength. f is frequency. Yes, for transmission, the oscillation source would be placed where R is shown. It is not about moving electrons. It is about field propagation. In some antennas, propagation speed will be less than the speed of light in a vacuum. This occurs when the electric field propagates inside a dielectric material other than air or vacuum. – mkeith Oct 3 '16 at 15:35
• @mkeith, yes, it is about field propagation, but the fields are created by current flow in the transmission mode. – Chu Oct 3 '16 at 15:51
• Yes, fields are created by (electron) currents. So, they must be the same. Yet, I know that electrons are millions times slower? – Little Alien Oct 3 '16 at 19:25
• When considering electromagnetic waves, it is not useful to think about electron flow. It impedes understanding. In general, electrons move if they are free (which they are in conductors) and if there is an electric field present. Under certain conditions, a time varying electric (or magnetic) field can give rise to a traveling electromagnetic wave, which can travel through free space without any conductors anywhere around. – mkeith Oct 5 '16 at 4:57