Antenna Polarization: Fixed E-field Orientation?

In summary, the orientation of the E field in a fixed coordinate system is initially fixed in the direction of propagation until the wave encounters something that causes it to bend or reflect, resulting in a change in orientation. This is why TV antennas in one area are usually all horizontal or vertical. However, the HP and VP only apply to transmissions in the direction of the main beam of a directional antenna and can vary depending on the geometry of the environment. Circular polarization is often used to mitigate this effect.
  • #1
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Suppose we have a fixed coordinatre system (x,y,z). Suppose an antenna is horizonally polarized. Is the orientation of the E field fixed as a function of (x,y,z). Or does it change?
 
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  • #2
It is fixed until the wave bends or bounces off something like an ionized layer in the sky or a solid surface. After that, it may exit at a different orientation.

This is why you will usually see all the TV antennas in one area are all horizontal or all vertical.
 
  • #3
Thanks.
I was thinking that since the E field is always in the plane orthogonal to the progagation direction, that the orientation of the E field must depend on (x,y,z). i.e Different locations would have different progagation directions, so the E field would be oriented differently.
 
  • #4
The HP and VP really only apply to transmissions in the direction of the main beam of a directional antenna and only then when you are talking about transmissions parallel with a flat ground.

All you can really say is that the E field is normal to the direction of propagation. How would you define VP if the beam were arriving vertically at the ground, for instance? For anything but propagation parallel to the ground, there is an element of Horizontal E field, in fact, even if it was originally launched as perfectly VP. (and vice versa.) It's a geometry thing and can seriously hurt the brain.
It's a real nightmare when you try to consider what happens to a linearly polarised wave, launched from a 'feed' when it spreads out and hits a parabolic reflector. The surface of the reflector is in all sorts of planes and the polarisation that emerges from each point is changed on reflection. This effect is less (through cancellation) when the dish is symmetrical but many dishes have 'offset' feeds (look on the sides of some nearby houses). It is common to use circular polarisation which helps in this respect.
 

1. What is antenna polarization?

Antenna polarization refers to the orientation of the electric field of an electromagnetic wave as it propagates through space. This orientation is typically described as either horizontal, vertical, or circular.

2. What is fixed E-field orientation in antenna polarization?

Fixed E-field orientation refers to the specific direction in which the electric field of an antenna is oriented. This is typically determined by the physical design of the antenna and cannot be changed once it is constructed.

3. How does antenna polarization affect signal reception?

The polarization of an antenna must match that of the incoming signal for optimal reception. If the polarizations do not match, there will be signal loss and reduced performance.

4. What are the advantages of using fixed E-field orientation in antenna design?

Using a fixed E-field orientation in antenna design allows for better control and optimization of the antenna's performance. It also reduces the complexity and cost of the antenna design.

5. Can an antenna with fixed E-field orientation receive signals of different polarizations?

Yes, an antenna with fixed E-field orientation can still receive signals of different polarizations, but there may be reduced performance and signal loss. It is best to use an antenna with a polarization that matches the incoming signal for optimal reception.

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