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I am writing a paper, in which I perform experiments with electromagnetic radiation. In some tests, I radiate interference all over the target, while in others I use a very directed antenna to radiate on a precise location of the target. I am looking for noun that could describe this differentiation (local radiation versus global radiation). I thought of "extensiveness" but it sounds too philosophical for me, is there a more fitting term?

I can't provide an example sentence since it would be used as a column header in a table.

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Dissipation? (as in, total concentration on a single point would have dissipation of zero, and maximum spread would have dissipation of 100). Or Concentration, which would be the reverse. I'm not a scientist but these terms would seem to describe what you're looking for. – Charl E Feb 29 at 13:44
    
Tightness of beam (with deference to E E Smith). – Edwin Ashworth Feb 29 at 13:50
    
Surely you'll refer to the column heading in the text? Anything you can put there? – jimm101 Feb 29 at 14:03
    
I'm describing whether the target is "attacked" globally or locally, but it has to describe the testing environment, more than the physical nature of the beam/field etc... so those terms won't fit. @jimm101 I'll try to come up with an example – MaximGi Feb 29 at 14:07
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The noun "focusing" may fit to refer to antennas beam (narrow-beam for directional antennas, isotropic pattern of omnidirectional antennas). – Graffito Feb 29 at 16:48
up vote 14 down vote accepted

How about scope?

the extent of the area or subject matter that something deals with or to which it is relevant

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I think this is an appropriate word, thank you. – MaximGi Feb 29 at 14:18
    
"Scope" in this sense typically refers to the boundaries of a body of information, not physical phenomena. For instance, the scope of a design document might be limited to a specific car part. – txteclipse Feb 29 at 19:21
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@txteclipse I would find it natural enough to refer to the scope of the beam. – Scimonster Feb 29 at 20:31
    
In fact, it's the scope of the experiment we're talking about. (not about antennas or beams, in that case I wouldn't had to ask for a word here) – MaximGi Mar 1 at 7:48

Diffused vs focused would be good enough to distinguish between the two.

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If the irradiance is higher in the focused state (i.e. the same amount of energy is focused on a smaller area), then this is correct. If the irradiance stays the same then this isn't quite right. – txteclipse Feb 29 at 19:27
    
@txteclipse Even if the radiation isn't "focused" in a technical sense, both focused and diffused can be used non-technically to express the intended meanings of "spread out" and "narrowly centered". This answer would be better with some definitions. – DCShannon Feb 29 at 19:38

Well, if you're writing a formal scientific paper, it would probably be best to ask a scientist in your field what the right term is.

As a layman, though, I suggest dispersion, which is defined by oxforddictionaries.com as "the state of being dispersed over a wide area". So one might say that one test is characterized by low dispersion, while the other is characterized by high dispersion.

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Grouping” is a noun associated with target shooting, which might be relevant or at least transferable to your context.

Shot grouping
In shooting, a shot grouping, or simply grouping, is the placement of multiple shots on a target, the shots taken in one shooting session. The closeness of the grouping, the nearness of all the shots to each other, is a measure of the accuracy of a weapon, and a measure of the shooter's consistency and skill.

The grouping of shots can range from “tight” to “scattered.”
(definition of “grouping/shot grouping” from ‘Wikipedia’ and example usage of “tight” and “scattered” groupings from ‘Wildlife Study Design’ by Michael L. Morrison, W.L. Kendall, William M. Block, M. Dale Strickland, via ‘Google Books’)

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For some types of radiation (namely sound and light) the term of art is beam spread, or sometimes field angle or beam angle.

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