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  1. #1
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    E and H antenna directivity plot understanding

    From Joseph Carr book "practical antenna handbook" he states if an antenna is vertically polarized then the E field is vertical to earth and if horizontally polarized that H field is horizontal to the earth.

    So how does Carr statement relate to my attached antenna E field pattern? Where is my physical location if I were to view the vertical antenna radiation?

    Where am I physically located if I were to view the horizontal antenna radiation?

    Does the plot tell me what my antenna gain is?

    How do you tell if the antenna has better H field or E field performance?

    Is there a way to tell if the antenna is vertically or horizontally polarized just by looking at the radiation pattern?


    •   Alt15th June 2012, 07:22

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    Re: E and H antenna directivity plot understanding

    Quote Originally Posted by robismyname View Post
    From Joseph Carr book "practical antenna handbook" he states if an antenna is vertically polarized then the E field is vertical to earth and if horizontally polarized that H field is horizontal to the earth.
    That's basically right. For linear polarisation, the direction of polarisation is that of the E field.

    Quote Originally Posted by robismyname View Post
    So how does Carr statement relate to my attached antenna E field pattern? Where is my physical location if I were to view the vertical antenna radiation?
    It is normal to talk of "azimuth" and "elevation" in antennas. If the antenna is vertically polarized, then the E-plane diagram shows you how the antenna behave with elevation. The H plane diagram shows you how it behaves along the horizon (aziimuth). If the antenna is horizontally polarised, then these patterns are reversed.

    Quote Originally Posted by robismyname View Post
    Where am I physically located if I were to view the horizontal antenna radiation?
    I would try to stop thinking of horizontal and vertical plots, and use the propor terms. I've stated them above.

    Quote Originally Posted by robismyname View Post
    Does the plot tell me what my antenna gain is?
    E and H plane plots can sometimes tell you the gain. Sometimes the plots are shown as absolute values in dBi. In that case, you can tell the gain. For the plots you have shown, the figures are just relative, with a peak value of 0 dB. As such, you can't ascertain the gain.

    Quote Originally Posted by robismyname View Post
    How do you tell if the antenna has better H field or E field performance?
    You need to define better.

    Quote Originally Posted by robismyname View Post
    Is there a way to tell if the antenna is vertically or horizontally polarized just by looking at the radiation pattern?
    Not in general. But if you knew the antenna was a dipole, and had elevation and azimuth plots, you could work it out quite easily.

    I would add, the plots you show seem a bit odd. What sort of antenna is this?



    •   Alt15th June 2012, 11:43

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  3. #3
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    Re: E and H antenna directivity plot understanding

    Thanks for responding........I apologize in advance with all the trivial and meticulous questions. I hope you can understand what Im trying to ask.

    Quote Originally Posted by DeboraHarry View Post
    It is normal to talk of "azimuth" and "elevation" in antennas. If the antenna is vertically polarized, then the E-plane diagram shows you how the antenna behave with elevation. The H plane diagram shows you how it behaves along the horizon (aziimuth). If the antenna is horizontally polarised, then these patterns are reversed.
    so elevation corresponds to E field, that are vertical. So you are looking at antenna radiated energy in a plane that is is perpendicular to the earth?

    so azimuth corresponds to H field, that are horizontal. So you are looking at antenna radiated energy in a plane that is parallel to the earth?

    So the plots should not be referred to as vertical or horizontal but instead only the physical position of the antenna should be referred to as vertical or horizontal?

    Or just think about vertical and horizontal in terms of the E and H fields?

    Quote Originally Posted by DeboraHarry View Post
    E and H plane plots can sometimes tell you the gain. Sometimes the plots are shown as absolute values in dBi. In that case, you can tell the gain. For the plots you have shown, the figures are just relative, with a peak value of 0 dB. As such, you can't ascertain the gain.
    I did a quick google search and could not find a relative antenna plot (like mine) that has gain. There was this one plot I attached below that is a relative antenna plot but it list what the gain is. I dont thin the gain was obtained form the relative plot I think they obtained the gain using some other measuring method and pasted the gain information on the relative plot.



    I have not found a relative plots that shows gain except the one I show above. Does that indicate gain is not of importance when plotting relative pattern only directivity? I did see a few absolute antenna plot but to me it seems this plot is derived with a VNA perhaps and not from the raw data from the turntable/rotation 6M test? I still have the raw data from the test setup. Like I mentioned the test setup was the typical turntable/rotational technique with 6M separation between the TX and RX. Can i reformat the data to provide the gain?

    Quote Originally Posted by DeboraHarry View Post
    You need to define better.
    What I was trying to say was that it you have the E plane plot and H plane directivity plots in front of you can you determine if the antenna is a vertically polarized or horizontally polarized antenna, just by looking at the directivity patterns? I mean if an antenna is vertically polarized and its turned 90 degrees to horizontal you should not expect it to perform as good if it was vertically polarized, correct?. I would expect to see this behavior portrayed in the directivity plots somehow. Isnt there an optimal fixed position of the antenna in the E field if its vertically polarized? and vice versa for horizontally polarized antennas?

    Quote Originally Posted by DeboraHarry View Post
    Not in general. But if you knew the antenna was a dipole, and had elevation and azimuth plots, you could work it out quite easily.
    Please define dipole for me. You mean 1/2 wave dipole with a center feed point and left right radiating element? So looking at my directivity plots one cannot determine if the antenna is horizontally or vertically polarized?

    Quote Originally Posted by DeboraHarry View Post
    I would add, the plots you show seem a bit odd. What sort of antenna is this?
    [/QUOTE]

    Can you elaborate on what makes it strange? Is it the fact that the greatest energy is not pointing at 0 degrees? But instead 180 degree on E plan pattern and 315 degrees on H plane pattern?
    I dont have a photo of the antenna I was testing but I made a quick sketch for you. Its basically like a pcb microstrip co-linear dipole antenna.



    Also the antenna plots I provided does determine that the antenna is dipole correct? Do you look at just the E plot to determine if it is a dipole?

    I noticed that my H plane plot looks different than alot of other antenna H plane plots. I see other H plane plots look more like a complete circle. See attached.



    As you can see mine does not look like this. Is this an indication of bad design?



    •   Alt15th June 2012, 17:58

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  4. #4
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    Re: E and H antenna directivity plot understanding

    Quote Originally Posted by robismyname View Post
    Thanks for responding........I apologize in advance with all the trivial and meticulous questions. I hope you can understand what Im trying to ask.

    Originally Posted by DeboraHarry:
    "1) It is normal to talk of "azimuth" and "elevation" in antennas. If the antenna is vertically polarized, then the E-plane diagram shows you how the antenna behave with elevation. The H plane diagram shows you how it behaves along the horizon (aziimuth).

    2) If the antenna is horizontally polarised, then these patterns are reversed."

    so elevation corresponds to E field, that are vertical. So you are looking at antenna radiated energy in a plane that is is perpendicular to the earth?

    so azimuth corresponds to H field, that are horizontal. So you are looking at antenna radiated energy in a plane that is parallel to the earth?

    So the plots should not be referred to as vertical or horizontal but instead only the physical position of the antenna should be referred to as vertical or horizontal?

    Or just think about vertical and horizontal in terms of the E and H fields?

    Please, robismyname, think back in time when radio was first being invented and the first antennas were very long or tall structures. We will think in terms of tall and not 'long' for this discussion.

    Think of the common commercial AM Broadcast Band antenna (530 kHz thru 1700 kHz), which for 1 MHz frequency the 1/4 Lambda length is about 250 feet or 76 meters, straight up. We will ignore 'ground radials'.

    The orientation of this antenna's Electric field is vertical, matching the vertical orientation of the 1/4 wave element which possesses a voltage gradient along its vertical length, low voltage at the bottom and high voltage at the top. Their is also an associated magnetic field, high at the bottom and low at the top, but I will ignore it for the moment.

    Now, we refer to what DeboraHarry posted:

    "1) It is normal to talk of "azimuth" and "elevation" in antennas. "

    . Azimuth - relates (for our case with the vertical AM Broadcast antenna) to compass bearing.
    . Elevation - is the angle 'up' (or down as well, if the antenna were in free space we could plot this part of the pattern too)

    "2) If the antenna is vertically polarized, then the E-plane diagram shows you how the antenna behave with elevation. "

    . At the horizon, then, at zero degrees elevation the 1/4 wave vert has its strongest response or signal
    . At straight up the 1/4 wave vert has very little (theoretically zero) response or signal.

    "3) The H plane diagram shows you how it behaves along the horizon (aziimuth). "

    . At the horizon are where the people who hear your broadcast reside.
    . Looking at all compass 'bearing' (Azimuth) angles gives you the H-plane response. It will be equal in all directions for our 1/4 wave vert.

    "4) If the antenna is horizontally polarised, then these patterns are reversed."

    Yup.


    RF_Jim
    Last edited by RF_Jim; 15th June 2012 at 18:46.



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