Talk:Radiation pattern

message: Hi - if there's anyone out there. I've created some 3D far field plots (:Image:Radiation-patterns-v.png), and intend to put them on this page. In order to have enough text to go with both the existing and new images, I reckon I'll add some words defining cuts (great-circle and maybe conical cuts) through the pattern. Stop me now if you don't agree! --catslash 00:25, 1 August 2006 (UTC)
thread_title:  3D far field plots 

message: I'm going to replace the article lead (?), to emphasize the distinction between the far-field pattern and the near-field pattern, and to reflect the fact that radiation pattern can mean either (I'll also make this distinction in the reciprocity section). Here's what I'm snipping out..
:A radiation pattern refers to the spatial variation of the electromagnetic fields, the field intensity, and/or the irradiance (power density), produced in the far-field from a localized source.  Most commonly, the radiation pattern is described for a source in a homogeneous medium (typically vacuum or air).
:For example, it can refer to the radiated field of a radio or microwave antenna, the power distribution radiated from the end of an optical fiber, the pattern of light from a light-emitting diode or laser, and similarly for many other devices.  The radiation pattern generally depends on the precise source geometry and the wavelength of the radiation.
:The radiation pattern is often represented graphically by the power distribution as a function of angle, in the plane of maximum radiation or in the E-plane and H-plane for  linearly polarized sources.
--catslash 13:25, 7 September 2006 (UTC)
replies: text: The new version looks good to me.  —Steven G. Johnson 23:44, 7 September 2006 (UTC)
thread_title: Near field radiation pattern

message: I don't get the logic in the end of the proof: "Analysis of a particular antenna (such as a Hertzian dipole), shows that this constant is , where λ is the free-space wavelength. Hence, for any antenna". It seems to me like a generalization to the general from the particular that is not obvious.  —Preceding unsigned comment added by 80.216.130.104 (talk) 10:11, 7 March 2009 (UTC)
replies: text: It's intended to be in the immediately preceding sentence: Furthermore, the constant of proportionality is the same irrespective of the nature of the antenna, and so must be the same for all antennas. --catslash (talk) 15:00, 7 March 2009 (UTC)
thread_title:  Missing logic? 

message: One question I always had on antenna gain plotting is the difference between rotating the antenna (with signal source attached) and recording the signal strength from a fixed location (same as walking around a fixed antenna with a receiver, taking the path of a constant radius circle and recording received signal strength), and walking around with a receiver and following the path of constant received amplitude.  The latter is what you would see if the transmitted energy was visible, the true shape of the field in space.  The former collects data about signal strength and therefore antenna gain at different angles, but if you plot it on linear or log scale, you don't get the real world spacial distribution of the energy.  If you superimposed an antenna pattern on a map, and assumed that people (with a receiver of a certain threshold) could receive the signal if they were inside the pattern, it would be the latter pattern only that would work, not the standard log gain plot.  In ideal space, the "walk around" iso-amplitude pattern would follow 1/r^2 rule after the antenna gain were applied in each direction.  Another issue here is if, in the walk around process, you had an antenna null that caused you to travel into the near field area of the antenna, some strange things would happen.  You would have to use enough power into the antenna so that your receiver would work everywhere outside the near field while walking the constant signal strength path.
I wish this Wikipedia article addressed these not so obvious issues with measuring and plotting radiation patterns.  I personally don't feel qualified to do this.  192.80.95.243 (talk) 16:33, 28 December 2010 (UTC)
replies: text: Yeah, to find the far-field pattern you want to stay out of the near field and transition regions, which can extend as much as 10 wavelengths from the antenna, which (as you say) might be difficult with your second method.  I'm pretty sure that at antenna testing ranges they use your first method, recording the signal strength at a constant distance.  The radial coordinate of radiation plots is signal strength (usually dBi), not range.     However (and here's what I think you were asking) on a decibel radiation plot, the radial coordinate IS proportional to the range contour that would give a constant signal strength!  The logarithmic nature of decibels removes the inverse square factor.  So a standard dB radiation pattern is also a pattern of the relative range you would get.  Just rescale the decibels to miles. --ChetvornoTALK 17:50, 28 December 2010 (UTC)
replies: text: An amplitude plot, (one where the radial scale is proportional to the field strength (amplitude) at a fixed (sufficiently large) distance), is also a plot of the distance travelled before the signal strength drops to some given constant level. This is because the field strength drops off like 1/r (the power is proportional to the square of the field strength, and so drop off like 1/r2). If you double the received field strength in a particular direction, then you have to stand twice as far away to bring it back to the same level. Amplitude plots are often used with low-gain antennas (like dipoles) and dB-scale plots used with high-gain antennas (like dishes). The radiated power, gain or directive gain plotted on a dB scale is also a plot of the logarithm of the distance travelled before the received power drops to a given level. All this assumes the distances involved take you out of the near-field of the antenna (if the largest dimension of the antenna is D, then further away than D2/λ and further away than (say) λ/2, whichever is the greater). I agree that distance reached is a nice intuitive way of understanding the plots - however I believe it's non-standard, and so would count as original research. --catslash (talk) 19:39, 28 December 2010 (UTC)
thread_title:  Pattern Plotting Concept