In this video you will learn what antenna beam width is, how to read it from the radiation diagram, and how it differs for antennas with symmetrical and asymmetrical radiation pattern.

The shape of radiation diagram determines the application of an antenna. The axis of maximum gain of directional antenna is called Antenna Boresight. If we cut the 3d diagram in horizontal plane, we call it azimuth cut, if we cut the diagram in vertical pane, we call it elevation cut.

When we speak about antenna beam width, we exclusively speak about the width of the main beam, also called main lobe. Antenna beam width is the angular width of the main lobe measured in azimuth and elevation cuts.

The most common approach is to measure the width of the main lobe till the power is half of the boresight power . The half power corresponds to -3dB in logarithmic scale. You can see this information next to the measured angle, for example: 75° azimuth beam width @ - 3dB.

Sometimes you can see -6 dB beam width in the datasheets. This is the angle between the points of the main lobe which are 6 dB below the maximum gain value. The -6 dB points correspond to quarter of the maximum radiated power.

How to correctly read beam width from the polar graph?

Boresight gain is usually at 0 degrees. Looking at the main lobe gain curve - find the spots where the gain is 3db less than the maximum gain, connect them with zero and measure the angle. For quarter power beam width, find the spots where signal drops 6 dB from maximum boresight gain and measure the angle.

If you perform measurement on an azimuth cut, you measure how wide the beam is in azimuth plane. On elevation cut, you measure the beam width in the elevation plane.

Antennas with Symmetrical main beam have identical azimuth and elevation beam widths, therefore one number is enough to describe them.

Antennas with Asymmetrical main beam have radiation pattern wider in azimuth and more narrow in elevation or vice versa. Therefore the beam width of these antennas has two values, one for azimuth and one for elevation.

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0:00 Intro
0:20 Basics
0:42 -3 and -6 dB beam width
1:11 How to read beam width
1:41 Symmetrical & Asymmetrical main beams

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