Talk:Directivity

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[edit] Directivity / Directive Gain

This article confuses directivity and directive gain. The function of direction is usually called the directive gain, and the peak directive gain (or the directive gain in the direction of interest) is called the directivity (see for example Orfanidis [1] and the IEEE dictionary[1]).

--catslash 18:04, 31 August 2007 (UTC)

OK - I stand (semi-) corrected; later editions of the IEEE dictionary (including the 6th ed. [1]) say that the term directive gain is now deprecated and that directivity should be used both for a given direction and for the maximum (If the direction is not specified, the direction of maximum radiation intensity is implied). However, I'd say that it's still common practice to distinguish the two terms (as in Orfanidis [2]). --catslash 10:06, 4 September 2007 (UTC)

[edit] Things to Add

Here're some things that the article could mention:

  • Reciprocity: The directivity is equally relevant to receiving antennas - also mention Friis transmission equation / link budget?
  • Partial directivity / partial directive gain (definition of).
  • Gain: The definition given here agrees with the IEEE definition[1] (so perhaps it should refer to radiation efficiency rather than the antenna efficiency). Nevertheless it's fairly common to define the gain so as to include the loss due to reflection at the antenna feed point (i.e. due to mismatch between the feed-line and antenna impedances) - and this ought to be be mentioned. See Balanis [2] who switches definitions between editions.

--catslash 18:04, 31 August 2007 (UTC) Note regarding the gain: the IEEE Dictionary[1] calls this quantity the realized gain; so

\begin{align}G_{realized} & = e_{match} G \\ & = e_{match} e_{rad} D \\ & = e_{antenna} D \end{align}
e_{match} = \frac{P_{acc}}{P_{feed}} = 1 - |s_{11}|^{2}
e_{rad} = \frac{P_{rad}}{P_{acc}} = \frac{P_{rad}}{P_{rad} + P_{loss}}
eantenna = ematcherad

where eantenna is the antenna efficiency, erad the radiation efficiency and Pacc is the power 'accepted' by or 'delivered' to the antenna from the feed. --catslash 16:05, 17 September 2007 (UTC)

[edit] References

  1. ^ a b c d Institute of Electrical and Electronics Engineers , “The IEEE standard dictionary of electrical and electronics terms”; 6th ed. New York, N.Y., Institute of Electrical and Electronics Engineers, c1997. IEEE Std 100-1996. ISBN 1-55937-833-6 [ed. Standards Coordinating Committee 10, Terms and Definitions; Jane Radatz, (chair)]
  2. ^ Constantine A. Balanis: “Antenna Theory, Analysis and Design”, John Wiley & Sons, Inc., 2nd ed. 1982 ISBN 0-471-59268-4