TN Parabolic Antenna Measured Data

TN: Parabolic Antenna Measured Data DRAFT

Technical Note: Importing into
Visualyse Gain Pattens of Parabolic
Antenna via Azimuth, Elevation Slices

Abstract: One way to define the gain patterns of antennas is via gain tables using measured data. This can increase accuracy by
ensuing the simulation closely models the actual gain pattern. One way to measure the gain pattern of antennas is by taking two
slices, one in azimuth and another in elevation, over all angles from -180 to +180. This Technical Note describes ways to import
this data into Visualyse Professional assuming the antenna is axially symmetric - for example, if it were a parabolic dish antenna.

Introduction • Gain table as 3D array of Gain(Azimuth,
Elevation)
The accuracy of the results from any simulation is
dependent upon the accuracy of the inputs. One way to Either of these could be used as described below.
match as close as possible a real-world scenario is to Typically, the process starts by getting the data in the
use measured gain patterns for the antennas used. figure across into Excel or other data manipulation tool
so it can be put in the required format and then pasted
An example gain pattern (typically measured but in this into Visualyse Professional.
case generated in Excel for this Technical Note) is
shown in the figure below: Axially Symmetric Gain Table

30 For gain patterns that are symmetric around a boreight
line, it is possible to enter a table as arrays of Gain vs.
20 Offaxis Angle
In Visualyse Professional this can be found by:
10
• First, create a new single beam antenna type
0 and select a circular cross-section beam

Gain (dBi) -10 • Then change the roll-off by clicking on “Change”
as shown below:
-20
Then click on the “Gain Table” option and the dialog will
-30 allow data to be pasted in to the dialog as shown below:

-40

-50 80 100 120 140 160 180
-180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 40 60
Angle from boresight (deg)

Az Gain El Gain

This approach generates two slices:

• The gain in the azimuth plane from -180 from
boresight to +180 from boresight

• The gain in the elevation plane from -180 from
boresight to +180 from boresight.

Typically, the peak gain is at boresight and a step size
such as 1 is used.

The question is then how to get this data into Visualyse
Professional so it can be used in analysis?

Import Options

Visualyse Professional includes a number of ways that
gain patterns can be imported, in particular:

• Gain table as 2D array of {Gain, Offaxis angle}

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30

20

10

0

Gain (dBi) -10

-20

-30

-40

-50 20 40 60 80 100 120 140 160 180
0 Offaxis angle (deg)

The resulting averaged gain pattern can then be
imported into Visualyse Professional as follows:

Now this allows the gain pattern to be defined as a single Full Gain Table
array of gain (dBi) vs offaxis angle (in degrees). The
offaxis angle here varies from 0 at boresight to 180 far The full gain table approach takes account of all four of
offaxis. the slices rather than requiring a function such as
average or maximum to include a single slice.
However, the measured data includes four slices from
0 at boresight to far offaxis: The first thing to note is that any measurement data that
contains just the four slices will result in loss of accuracy
• Azimuth slice from 0 to -180 compared to measuring the full grid of Gain(azimuth,
elevation).
• Azimuth slice from 0 to +180
The key when importing data of this format is to select a
• Elevation slice from 0 to -180 coordinate system that minimises these errors.

• Elevation slice from 0 to +180 In Visualyse Professional the full grid of Gain(azimuth,
elevation) can be entered using the shaped antenna
So, which of these tables is to be used? type, as in the following dialog:

Here there are a number of options:

1) Use the average value across the four slices

2) Use the highest gain value across all four slices

3) Select the slice that is most appropriate for the
scenario under consideration

4) Consider the two slices in the direction of
interest (i.e. either the azimuth or elevation
directions).

An example of the average gain (averaging in dBi) can
be seen below, where the average gain is shown in red
and the four slices are shown as black lines.

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It can be useful to duplicate the first/last line of data to
have a table a bit like this:

There are three problems to overcome: The data can then be pasted in and shown in the
preview – but only if the slice angle is set to 90:
1) This dialog shows a matrix of values whereas
the measured data is just two arrays The reason for requiring this slice angle is also the need
for an additional step.
2) The elevation array in the Gain(azimuth, In doing this transformation on the data, Visualyse
elevation) table only covers the range from -90 Professional must include a counter-rotation so that the
to +90 = 180 whereas the measured data in peak gain and boresight continues to be aligned with the
the elevation direction extends over 360 antenna reference frame (azimuth, elevation) = (0, 0).
This can be achieved using the multiple-beam antenna
3) The grid around boresight is rectangular in type option as that includes the ability to set the pointing
(azimuth, elevation) whereas the cross-section
is circular, making interpolation more
complicated.

A solution is to not set the antenna boresight to align
with (azimuth, elevation) = (0, 0) as is usually the case
but change the boresight line to be (azimuth, elevation)
= (0, 90).

This can be imagined as the “North Pole” of this gain
pattern if you map (azimuth, elevation) = (longitude,
latitude). Then the four slices can be considered as
mapping onto lines of longitude = lines of azimuth,
covering elevation = -90 to +90 which corresponds to
offaxis angles from 0 to +180.

This can be considered similar to a (, ) coordinate
systems where:

 = angle from boresight to test direction

 = angle from horizontal to line from boresight
to test direction

In this case, due to the rotation the  angle has been
mapped to azimuth and  = 90 – elevation.

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4|P a g e ( , ) = + ( )

of the beam. The boresight will line up if rotate the + ( ) [ ( = 90) − ( )
elevation as follows: ( = 90) ]

Having done this the antenna type can be attached to It can also be necessary to match which part of the
any station in the normal way. elevation data is used with which parts of the azimuth
data. In particular:
Combining Other Gain Tables
Front hemisphere:
The two approaches above made sense because the
data could be seen to be symmetric around a boresight −90 ≤ ≤ +90
with near circular cross-section
For other patterns, different methods could be used to −90 ≤ ≤ +90
combine the Gain(azimuth) and Gain(elevation)
measured data which could result in closer Rear hemisphere:
approximations to the actual antenna gain pattern.
As an example, for the types of antennas that are used −90 > > +90
for terrestrial mobile systems it can be useful to use the
Gain(azimuth, elevation) table but combine the two −90 > > +90
slices to get a value for each point on the matrix.
This combination can be achieved using a number of Future Versions
methods. The simplest is to add the two relative gain
values to the peak gain as in: We have been looking at ways to improve Visualyse
Professional and the updating the handling of antenna
( , ) = + ( ) + ( ) types is high on the list.
However, this can lead to very low far-offaxis gain
values. For example, if the Grel(Az) and Grel (El) both Watch this space!
tend to (say) -30 dB far from boresight, the resulting gain
will be 60 dB below boresight, which is unlikely. About Transfinite
This can be resolved by enforcing a floor to the
calculation, such as: We are one of the leading consultancy and simulation
software companies in the field of radio
( , ) = + ( ( ) + ( ), ) communications.
For some tables, this approach can lead to
discontinuities around the elevation = ±90 points. In We develop and market the market leading Visualyse
which case it can be helpful to use a smoothing function products:
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