Rotation rate of circular pol. waves

jo.thalbach

Newbie level 5
Hi,

Assume there is a 1 GHz circular polarized EM-wave. Can we say the electrical field rotates at the rate = 10^9 rotations/s?

vfone

A full rotation it happen at one cycle or one Hz.

albbg

A full rotation it happen at one cycle or one Hz.

It's not correct. Every wavelength the EM-field make a complete revolution. Since the wavelength is given by:

$\lambda$=$\frac{c}{ f}$

where f is the frequency and c the velocity of light the a complete revolution will be completed in

t=$\frac {\[\lambda$}{c }\]=$\frac{1}{ f}$ that is the period

this means the angular rotation rate equals $\omega$, the angular frequency or "f" rotation/s as said in the OP

vfone

The initial question was, if at 1GHz circular polarization, can we say the electrical field rotates at the rate = 10^9 rotations/s?
So in your view, at 1GHz circular polarization, how many (full) rotations would be during one second?

albbg

As I said the rotation rate is "f" rotations/s, that is at 1GHz we will have 10^9 rotations/s

ferdem

Full Member level 2
Yes, the field rotates at the same rate with the frequency.
Let us start with simpler case, linear polarization. In linear polarization the field changes its direction at the rate of the frequency driven.
Imagine a vector oscillating in +x and -x directions.
In circular polarization, you add a vector oscillating in +y and -y directions with 90 degree phase shift. Addition of these vectors will give a rotating vector, it rotates at the same rate.

vfone

Sorry, was a misunderstanding. Of course, the rotation rate is equal with frequency.

jo.thalbach

Newbie level 5
A further question: what if there is a bandwidth, say 1 MHz? Would the rotation rate be blurred?

ferdem

Full Member level 2
The rotation rate should be the instantaneous frequency of the signal. The modulation does not complicate it. It is not expected to see a extraordinary effect on the polarization in a simple medium (homogeneous, non-dispersive, isotropic).
However, the polarization may undergo interesting effects in an anisotropic medium. It can be changed from RHCP to LHCP for example. The rate should still be the same.

jo.thalbach

Newbie level 5
What do you mean with instantaneous frequency? Do you mean the rate will vary between 1.000 GHz and 1.001 GHz?

ferdem

Full Member level 2
The rotation rate is nothing but the frequency of the signal itself just like the case for linear polarization.
If it is changing in 1 GHz and 1.001 GHz, yes, the rotation rate will vary between those frequencies.

jo.thalbach

Newbie level 5
It’s clear the rotation rate is determined by the signal frequency, but for a signal with 1 MHz bandwidth the signal frequencies aren’t unique.

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