CWNA book Ed.3, page 80 ?¡é?€?¡° Azimuth and Elevation Charts
Last Post: May 24, 2006:
I?¡é?€??m fairly confused about this area and Googling hasn?¡é?€??t helped much.
Is Azimuth = E-plane = plane of polarization?
If this is correct, then on page 80 where it says,
?¡é?€??The azimuth shows a top-down view of the antenna?¡é?€??s coverage?¡é?€??
would only be so if the antenna was horizontally polarized, right?
Thanks for any clarification.
This is referring to an antennas coverage pattern. Azimuth refers to the coverage pattern if you could look straight down on the antenna. For example, if you looked straight down on an omni antenna, you would see that it has a coverage patter of 360 degrees. Now, look at the antenna from the side (elevation). Now, that same antenna from the side may have a coverage pattern from about 7 - 90 degrees.
I did a google image search for antenna patterns, but a lot of them just look really complicated and I didn't want to make this confusing. Let us know if this clears it up for you.
Thanks for taking the trouble to reply.
Unfortunately this does not clear up my understanding.
It seems to me that terms like "looked straight down " and "look at the antenna from the side" are ambiguous unless the polarization (vertical or horizontal) is established first.
I'm also trying to establish what the correlation is between these terms,
- plane of polarization
What I'd really like is for my original posting to be confirmed as correct or corrected.
Lastly - with this Forum environment (which I've seen many places & been confused with), why, when I click on Reply, does it ask for a Subject when I'm just continuing a thread? I would have thought the Subject was established at the beginning of a new thread and wouldn't change for the life of the thread ?!?!
You original post is not correct.
Azimuth = What the antenna radiation pattern looks like if you are up in an airplane looking straight down on the antenna. This is the top-down view you talked about in your original post.
Elevation = What the antenna radiation pattern looks like if you are standing on the ground looking at the antenna from the side
Polarity (either horizontal or vertical) is not dependent upon the azimuth and elevation. One is not affected by the other.
Polarity is simply this. Either the wave goes up and down, like the waves in water, or the waves go side to side like a snake crawling across the desert.
Azimuth and Elevation are in reference to the pattern in which the antenna disperses its power. Some antennas are like a shotgun (Yagi) and others are like a rifle (parabolic grid - dish).
Now, within that pattern you have to "see" whether the waves are going up and down (vertical polarity) or side to side (horizontal polarity).
When you look at an azimuth and elevation chart, you can't tell how its polarized.
Sorry for all of the pieces of information. You are just a victim of stream of consciousness. :) If this doesn't help, post back and I'll try again.
Oh, about the forum. Don't worry about the subject line unless its an inital post. I don't ever use it otherwise.
Thanks for your generous reply and patience. I think I feel some clarity starting.
1) In response to your,
?¡é?€??When you look at an azimuth and elevation chart, you can't tell how its polarized.?¡é?€??
I guess that?¡é?€??s why the charts are labeled E and H (which ties directly to polarization) not Azimuth and Elevation (which is independent of polarization), right?
2) As an example to confirm my understanding of what you said, if I drew an azimuth chart of an omni-directional antenna which was horizontal (so it?¡é?€??s horizontally polarized) I?¡é?€??d see the classic figure-of-8 front and back lobes whereas if I drew an azimuth chart with the same antenna vertical (so vertically polarized) I?¡é?€??d see the 360degree uniform circle, right?
3) Is it correct that for the same antenna (eg. a simple omni-directional), if it is horizontal, the azimuth chart will be the same as the Elevation chart for this antenna if it was vertical?
4) So is azimuth ALWAYS horizontal irrespective of antenna polarization ?¡é?€?¡° horizontal or vertical, and E is only equal to azimuth for a horizontally polarized antenna, right?
5) From your first post,
?¡é?€??if you looked straight down on an omni antenna, you would see that it has a coverage patter of 360 degrees?¡é?€??
Does this assume a vertically polarized antenna?
?¡é?€??For example, if a YAGI antenna is mounted with the radiating elements oriented vertically it will produce a vertically polarized signal. The azimuth pattern would then correspond to the co-polarized pattern (in the plane of the elements, sometimes called the E-plane, or the plane of the electric field produced by the antenna).?¡é?€??
This confused me because it seemed to be saying that if RF is vertically polarized, Azimuth is then vertical whereas I think you are saying Azimuth is always horizontal. Could you please clarify?
7) Is there really such a thing as Azimuth charts from antenna manufacturers? In the small time I?¡é?€??ve been kicking around the WLAN field I?¡é?€??ve only seen E & H charts.
ps: the water & snake analogies are great.
This is why I like teaching in person. In a classroom, I have a whiteboard. :)
Ok. Here goes.
An antenna doesn't know how it is mounted. An obvious statement, but important.
Lets take a doughnut. A big doughnut. Now, holding that doughnut in front of you flat in your hand represents an omni directional antenna. Imagine the antenna being right in the middle of that doughnut, coming up through the hole. The doughnut represents the azimuth and elevation patterns. If you look straight down on the doughnut, it covers equally 360 degrees. From the side, it covers a different pattern.
Ok. Normally, an omni antenna like that is polarized vertically. So, looking at the doughnut flat in your hand, the waves are going up and down. Now, what if someone mounted the antenna sideways? Turn the doughnut on its side, looking like a wheel on a car. Now, the waves are going side to side like the snake right? So, we changed the polarity of the antenna by mounting it differently. Now, look at the coverage pattern. Its all messed up. Its now shooting straight up into the air and down into the ground. That is why omni antennas 99.99999% of the time mounted straight up and down (doughnut flat).
Now, lets talk about a directional antenna. Don't worry about whether its a Yagi directional grid whatever. Now we have a footlong Subway in front of us. The directional antenna is located on one end of the sub. Unlike the omni antenna, when we look at the sub from the top or the side, it still has the same pattern, right? Now, for polarity. This all depends on how you mount the antenna. A directional antenna will have a sticker on it with an H (horizontal) pointing one direction and a V (vertical) pointing 90 degrees out from the H. So, if you want to mount it with the waves going up and down, point the V up. If you want the waves side to side, mount it with the H up.
Digest that for a bit and get back to me. I'm going to Subway for dinner and hitting a Krispy Kreme on the way home. Out.
Once again thanks for your response.
Why are they called "Azimuth and Elevation" charts on page 80 but the figures on page 81 (which are typical of what antenna manufacturers publish) are labelled E-Plane and H-Plane.
Try this page:
They just refer to the beamwidths (coverage patterns) of the antenna. I usually refer to the beamwidths as vertical beamwidth (looking from the side) and horizontal beamwidth (looking from the top). In the end, all of the terms are trying to describe the same thing, which is the coverage pattern of the antenna.
Thanks very much GTHill, I think I get it.