Is it common to have to consider the curvature of the earth?

[Alan0354]

I am studying antenna theory, there is a section talking about the effect of the curvature of the earth on the reflected signal. Is this important for antenna design? It seems that the only time it's important is if this is for satellite, aviation and space application. The more common cell phone, radio and tv can use the flat surface approximation. Is that true?

 

[davenn]

for terresterial microwave links, yes taking curvature into account is important particularly on links that are of any distance.
Its going be a determining factor in how high your antenna mast needs to be to get a line of sight path.
Hence what many linking systems are on hilltops, one of the reasons is to keep LOS over a given path.

Dave

 

[WimRFP]

Hello,

For antenna design, it is not important, but for the link budget calculation it can be of prime importance.

As davenn says, you need higher masts to get LOS over real earth then when assuming flat surface.

As long as your propagation problem is well within the line of sight distance, you can ignore it. For TV you can't ignore it as TV towers normally cover large distance. In case of interference calculations (for frequency sharing), you can't ignore it also, as propagation beyond line of sight is dominated by diffraction over curved earth (and not to forget tropospheric ducting/scattering/etc).

With regards to reflection, you can assume flat earth to calculate reflection coefficients (for example using the Fresnel reflection formulas) in case of ground-ground communication. In case of significant height above ground (for example sattelites), you need to take into account that after reflection the radiation spreads out due to the curvature.

 

[chuckey]

when you plot the path of a UHF TV signal you use a special pre-printed sheet, this has a section of the earths surface drawn with a radius of 4/3 of the earths actual radius. Then extra curves above it calibrated at 100, 200, 300, 400,500. . .feet. So you lay your line out on a map and mark the contour position on the pro-forma. then a straight line on the pro-forms then becomes the actual path. Now Fresnel zones, they are a different matter. :-(
Frank

 

[shashy.br]

If your antenna (Radar) is ground based, the Curvature of the earth affects the Maximum detection Range,consider a Surface Surveillance application , the detection range is limited by the Radio Horizon.

The radar can only detect beyond the Radio horizon only in certain conditions of the atmosphere (Anomalous propagation conditions).