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  • Hi,

    I think I've finally grasped that an azimuth plot represents a 'top down' view (e.g. say you had an AP mounted on a wall, the azimuth plot would be as if you were sat on top of the wall looking down at the AP), and an elevation plot represents a side view (e.g. if you were standing against the wall with your left arm touching it, looking along the wall (parallel to it), and with the side of the same wall mounted AP facing you) - the elevation plot would show the propagation from the ceiling down to the floor.  I think that's right isn't it ?

    Therefore, if you mounted the same AP on the ceiling, facing down, (and you were laying on top of the ceiling, looking down at the back of the AP), the azimuth pattern would represent the propagation in a left-right plane and the elevation pattern would be 90 degrees to this, i.e. in the 'head to toe' plane.

    If I've got all that correct (and I'm not certain I have !), then what on earth is going on here.... ???

    https://meraki.cisco.com/img/products/wireless/mr18/coverage-diagrams-2-4-horizontal.png

    How can that represent an elevation plot if the AP is facing you ???

    I don't get it !

    HELP !!!  :-)

  • The view is from above or below - and is its azimuth pattern.

    It is often easy to become confused when looking at patterns for omni-directional antennas. Also, in a high percentage of diagrams, there has been a disconnect between the engineering staff and the art department, and the views get reversed.

    If you compare both elevation and azimuth diagrams on the MR18 brochure page, you'll only see a slight difference between these two.   The overall 3D pattern shows it to be more or less omni-directional, which is what it is advertized to be.

  • Many thanks for that Howard.  I just have one other query, if you don't mind...  I don't know if you've used Airmagnet planner, but when you start planning an installation, it requires you to pick the AP / antennas you intend to use, so that it can predict the coverage accordingly.  However, it lists each AP / antenna twice - one for azimuth and the other for elevation.  Why is this ?  Is this for wall / ceiling mounting ?, and if so, which is which ?  Also, it allows you to rotate the antenna too - but which way is it pointing when you pick zero degrees (default) ?

    I'm amazed I just can't find this information anywhere !

  • By Howard - edited: June 7, 2015

    Sorry, I have not used it. 

     You can see by the Signal Coverage Patterns, for both 2.4 and 5 GHz, that the angle that Cisco (Meraki) uses is shown on their charts, is in relation to the Cisco Emblem at one end of the unit.   If for no other reason than consistency, I would stay with that.

    BTW, you should notice that the AP shows a noticeable amount of Down Tilt when looking at the side views for either band.

    If nothing else start with a sphere, with the AP at the center, and equal radiation in all directions - with the correct gain values for each band.

    Remember this is a predictive analysis.   You're expected to make adjustments to match reality after the simulation anyway.

    After you've run through things a couple times, it should become more clear.

    Somewhere there has to be documentation on the Airmagnet product that says how to take all this into account. 

  • By karlenr - edited: June 8, 2015

    In basic antenna engineering terms the default Azimuth is a polar reference  and can be measured with a compass with 360 & 0 degrees being due North. Elevation refers to a local pole and can be measured by a plumb bob and a protractor with zero degrees at 90 degrees normal to the horizon i.e. pointing straight up IN ALL CASES.

    The AZ/El charts make it relatively easy to predict how an an antenna will perform at your site- provided the antenna is mounted with same physical and magnetic plane polarity(i.e.physical/electrical horizontal and vertical orientation) as the chart. The classic example where AZ/EL charts are not the ideal tool is where a high gain sector antenna is mounted on a tower with a few degrees of tilt. The AZ/EL charts don't actually show the kidney shaped footprint counter intuitively facing away from the tower. The maximum gain intersection point on the ground is actually a parabola curved through both the AZ and EL max gain planes away from the tower.  . 

    When an antenna is measured at a range  measurements are generally made using the spherical co-ordinate system, phi and theta in local space with various other conventions to describe the maximum gain, polarity, beam width etc. In other words the antenna and the measuring signal source/sink can be in any position without reference to any conventional poles This paper

    http://ww2.nearfield.com/amta/AMTA07-0092-GFM_SFG.pdf

    gives a very complete description of the various antenna co-ordinate systems and how that affects visualizations. 

  • By Howard - edited: June 8, 2015

    Karlenr,

    You give a good, clear description.

    I found the paper interesting too, but I was surprised to read this part:

    "If only a linear copolar and cross-polar pattern are required, the operator may decide to locate the peak of the pattern and then rotate the probe’s angle so
    that the lowest value is received. This angle is the crosspolar angle. The copolar pattern is then measured 90° from this angle."

    From conversations I've had with our compliance team, I thought they used the maximum value's position for the next sweep.

    What difference in the results will this make ?

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