 Hey everybody, it's Tossos with RF Elements and today we'll be talking about antenna bean width and how to read a radiation diagram. The shape of a radiation diagram determines the application for any particular antenna. In this video I'll explain what an antenna beam width is and how to read it properly from a radiation diagram. Before we do, let me explain a few important things first. The axis of maximum gain on a directional antenna is called its bore site. If we cut a 3D diagram on its horizontal plane, we call this the azimuth cut. If we cut this diagram on a vertical plane, we call this the elevation cut. When we speak about antenna bean widths, we're exclusively speaking about the width of the main beam, also called the main lobe. An antenna beam width is the angular width of the main lobe measured in its azimuth and elevation cuts. The most common approach is to measure the width of the main lobe till its power is half of the highest power the antenna can radiate at its bore site. Half power corresponds to negative 3 dB on the logarithmic scale. You can see this information next to the measured angle, for example a 75 degree azimuth beam width at negative 3 dB. Sometimes you can see negative 6 dB beam widths in data sheets. This is the angle between the points of the main lobe which are 6 dB below the maximum gain value. The negative 6 dB points corresponds to a quarter of the maximum radiated power. So how do you correctly read beam width from a polygraph? Bore site gain is usually at 0 degrees. Looking at the main lobe gain curve, find the spots where the gain is 3 dB less than the maximum gain. Connect them with 0 and measure the angle. For quarter power beam widths, find the spot where the signal drops 6 dB from the maximum bore site gain and measure that angle. If you perform a measurement on the azimuth cut, you measure how wide the beam is in the azimuth plane. On the elevation cut, you measure the beam width in the elevation plane, or you may say you're measuring how tall the beam is. Antennas with symmetrical main beams have identical azimuth and elevation beam widths, therefore one number is good enough to describe them. Antennas with asymmetrical main beams have radiation patterns with different beam widths in both planes. Therefore these antennas have two beam width values. One for azimuth and one for elevation. So now you should be able to correctly read beam widths from a polygraph. Stay tuned for some of our next videos where we'll talk about other cool RF topics.