This example shows how to visualize the far fields for antennas and antenna arrays. Radiation patterns can be plotted in Antenna Toolbox™ using the
pattern function. The example explains different options available in the pattern function.
Create the Yagi-Uda antenna in the default configuration.
ant = yagiUda; show(ant);
To plot the radiation pattern of the antenna, specify the frequency at which the data needs to be plotted. If no angles are provided, the azimuth spacing of 5 degrees between -180 to 180 degrees and the elevation spacing of 5 degrees from -90 to 90 degrees, respectively, are assumed. By default, the 3D antenna directivity is plotted expressed in decibels.
freq = 300e6; pattern(ant, freq);
The list at top left corner of the figure window provides additional details such as minimum and maximum values of the quantity to be plotted as well as the range of angles where the data is plotted. In the lower left corner, there is the inset of the antenna. Rotating the radiation pattern rotates the antenna too. To remove the antenna image from the plot, unselect the Show Antenna button.
By default, the function pattern plots the overall directivity. To plot the directivity of the individual field components separately, use the Polarization flag. The options available are the directivity of the azimuthal electric field (H), the directivity of the elevation electric field (V), Right- handed circular polarization (RHCP) and Left Hand circular polarization (LHCP) components of the electric field. The plot below shows the directivity of the azimuthal component of the electric field.
pattern(ant, freq, 'Polarization', 'H');
Individual slices of the directivity can be plotted using a polar or rectangular plot, to give a better understanding of how the field varies in different planes. The plot below shows the total directivity in the elevation plane (a 2D radiation pattern).
pattern(ant, freq, 0, 0:1:360);
patternAzimuth multiple patterns and overlay them on the single plot. The plot below shows three radiation patterns at azimuthal angles of 0, 30 and 60 degrees.
patternAzimuth(ant, freq, [0 30 60]);
To plot thepatterns at fixed elevation angles, use the function patternElevation.
pattern function also allows us to visualize the patterns using a rectangular plot. This can be done by modifying the CoordinateSystem flag as shown below. By default, the flag is set to polar. Change it to rectangular to visualize the data in the rectangular coordinate system.
pattern(ant, freq, 0:1:360, 30, 'CoordinateSystem', 'rectangular');
To plot patterns at multiple frequencies on the same graph, use the function
pattern with the PlotStyle flag allowing a choice between Overlay or Waterfall style of plotting. The feature is important for the analysis of large-bandwidth antennas. The PlotStyle flag needs to be set to waterfall to display a waterfall plot. The default value of this flag is overlay.
pattern(ant, [300e6 400e6], 0, 1:1:360, 'PlotStyle', 'waterfall', ... 'CoordinateSystem', 'rectangular');
The third option for the CoordinateSystem flag is uv. This will plot the field data in the u-v coordinate system. The functionality is mostly useful for antenna arrays to visualize the array lobes.
pattern(ant, freq, 'CoordinateSystem', 'uv');
The pattern function also allows us to plot the linear field patterns. Different field quantities can be plotted by modifying the Type flag. By default it is set to directivity. It can be set to efield to plot the magnitude of the electric field. The plot below shows the normalized magnitude of the electric field.
pattern(ant, freq, 'Type', 'efield', 'Normalize', true);
The main beam is the region of the maximum radiation. In the present case, the main beam is along the z-axis. The half-power beamwidth (HPBW) is the angular separation in which the magnitude of the radiation pattern decreases by 50% (or -3dB) from the peak of the main beam. For example, we want to measure the width of the main beam in the elevation plane. The HPBW can be calculated as shown below
[bw, angles] = beamwidth(ant, freq, 0, 1:1:360)
bw = 52.0000
angles = 64 116
The beamwidth is calculated at a single frequency and in a specified plane by choosing the respective values of azimuth or elevation angles. We observe that the width of the main beam is 54 degrees; the beam is located between 64 degrees and 117 degrees in the elevation plane.
 C. A. Balanis, 'Antenna Theory. Analysis and Design,' p. 514, Wiley, New York, 3rd Edition, 2005.