Antenna Part 6. Antenna Beamwidth: Half Power Beamwidth (HPBW) & First Null Beamwidth (FNBW).

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Antenna beamwidth is the angular span of the main lobe of the antenna radiation pattern, representing the region where most of the power is radiated. Beamwidth is measured in degrees and can be specified in either the horizontal or vertical plane. The beamwidth of an antenna is an important parameter because it determines the directionality and coverage area of the antenna. A narrow beamwidth indicates a highly directional antenna that is well-suited for long-range communication, while a wider beamwidth is better suited for short-range communication and for covering a broader area.

Each antenna has a specific beamwidth pattern, but this pattern is not constant across all frequencies. Therefore, it is important to consider the frequency of operation when testing to account for beamwidth differences. Higher frequencies have a smaller wavelength; generally, higher frequencies have a narrower beamwidth and are more directional. The divergence of the beam is related to the frequency by a formula, making it fairly easy to account for these effects.

Beamwidth is commonly measured as the angle between two points on either side of the main lobe, also known as the half-power points or -3 dB points, where the radiated power drops to half of its maximum value. Beamwidth is measured in degrees and can be specified in either the horizontal or vertical plane.
Half-Power Beamwidth (HPBW)
First Null Beamwidth (FNBW)

Half-Power Beamwidth (HPBW): This is the most common way to express beamwidth. It measures the width of the main lobe at the points where the power is half or -3dB of the maximum power. It can be expressed in degrees and can be found both in the horizontal and vertical planes.

First Null Beamwidth (FNBW): It is the angle between the first nulls adjacent to the main lobe where the power is zero. The FNBW is an important parameter for antenna designers because it determines the antenna's ability to reject signals/interference from unwanted directions. A narrower FNBW indicates a better ability to reject signals from unwanted directions, while a wider FNBW indicates a lower ability to reject signals / interference from unwanted directions.

Indication of FNBW
Draw tangents on both sides starting from the origin of the radiation pattern, tangential to the main beam. The angle between those two tangents is known as First Null Beam Width (FNBW).

Relationship between beamwidth and gain

Antenna beamwidth and gain have an inverse relationship. Decreasing the beamwidth, i.e., having a narrow beamwidth, will result in a higher gain. This is because with a narrow beamwidth, power transfer is increased in a particular direction.

Relationship between the signal-to-noise ratio (SNR) & Beamwidth

As beamwidth is closely related to directivity and gain, changes in beamwidth cause proportional changes in both of these parameters. For a narrow beamwidth antenna, gain and directivity are higher, which will increase the signal-to-noise ratio (SNR) favorably. The SNR is the ratio of signal strength to unwanted interference (noise), and a higher SNR is always desirable.

Beamwidth describes how the signal radiates from an antenna and is expressed in degrees horizontally and vertically. For example, an omnidirectional antenna radiates its signal 360 degrees horizontally. It depends on the model; it might have as much coverage area as 75 degrees vertically. As such, it doesn't radiate its signal in a complete sphere around the antenna. Rather, it's more of a donut shape.

Antenna beamwidth is a useful analytical parameter for various practical applications, including:
Planning antenna coverage in a given area.
Determining whether neighboring antennas will interfere with each other.
Assisting in improving the performance of communication links.
Developing network mobility