AS (Angle Spread)

Angle spread (AS) is a term used in radio communication and radar systems to describe the angular spread of a signal or wavefront. It is a measure of the extent to which the signal energy is distributed over a range of angles. Angle spread is a crucial factor in determining the performance of a communication or radar system. In this article, we will discuss the concept of angle spread in detail.

Definition of Angle Spread

Angle spread refers to the range of angles over which a signal or wavefront is spread. It is a measure of the angular extent of the signal's energy distribution. In other words, it is the angular width of the signal as measured from its main lobe to its first null. The angle spread is usually defined as the difference between the two angles at which the signal amplitude falls to half of its maximum value. This is known as the half-power beamwidth (HPBW) and is denoted by θ.

The angle spread of a signal is determined by the physical characteristics of the transmitting and receiving antennas, as well as the wavelength of the signal. In general, the angle spread of a signal is inversely proportional to the size of the antenna aperture and directly proportional to the wavelength of the signal.

Types of Angle Spread

There are two types of angle spread, namely horizontal angle spread and vertical angle spread.

Horizontal Angle Spread

The horizontal angle spread, also known as the azimuth angle spread, refers to the range of angles over which the signal energy is spread in the horizontal plane. It is measured in degrees and is denoted by θh. The horizontal angle spread is important in radar systems that are used for target tracking and surveillance. In these systems, the radar antenna is rotated in the horizontal plane to cover a wide area of azimuth angles.

Vertical Angle Spread

The vertical angle spread, also known as the elevation angle spread, refers to the range of angles over which the signal energy is spread in the vertical plane. It is measured in degrees and is denoted by θv. The vertical angle spread is important in radar systems that are used for altitude measurement and aircraft detection. In these systems, the radar antenna is tilted in the vertical plane to cover a wide range of elevation angles.

Factors Affecting Angle Spread

Several factors can affect the angle spread of a signal. Some of the most important factors are discussed below.

Antenna Size

The size of the antenna aperture plays a crucial role in determining the angle spread of a signal. In general, larger antennas have narrower angle spreads, while smaller antennas have wider angle spreads. This is because larger antennas are capable of focusing the signal energy into a smaller beam, which results in a narrower angle spread.

Antenna Type

The type of antenna used can also affect the angle spread of a signal. For example, a parabolic dish antenna has a narrow angle spread in both the horizontal and vertical planes, while a dipole antenna has a wider angle spread. This is because the parabolic dish antenna is capable of focusing the signal energy into a narrow beam, while the dipole antenna radiates energy in all directions.

Signal Frequency

The wavelength of the signal is directly proportional to the angle spread of the signal. In general, higher frequency signals have narrower angle spreads, while lower frequency signals have wider angle spreads. This is because higher frequency signals have shorter wavelengths, which allow them to be focused into narrower beams.

Signal Bandwidth

The bandwidth of the signal can also affect the angle spread of the signal. In general, signals with wider bandwidths have narrower angle spreads, while signals with narrower bandwidths have wider angle spreads. This is because signals with wider bandwidths contain more energy, which allows them to be focused into narrower beams.

Signal Strength

The strength of the signal can also affect its angle spread. In general, stronger signals have narrower angle spreads, while weaker signals have wider angle spreads. This is because stronger signals have more energy, which allows them to be focused into narrower beams.

Applications of Angle Spread

Angle spread is an important parameter in many applications of radio communication and radar systems. Some of the most common applications are discussed below.

Radar Systems

In radar systems, the angle spread of the signal is crucial in determining the accuracy and resolution of the system. A narrow angle spread allows the radar system to distinguish between targets that are close together, while a wide angle spread can cause confusion between targets. Radar systems typically use antennas with narrow angle spreads to improve target resolution and accuracy.

Communication Systems

In communication systems, the angle spread of the signal is important in determining the coverage area of the system. A wide angle spread allows the signal to cover a larger area, while a narrow angle spread limits the coverage area. Communication systems typically use antennas with wide angle spreads to provide broad coverage.

Satellite Communication

In satellite communication systems, the angle spread of the signal is important in determining the coverage area of the satellite. A wide angle spread allows the satellite to cover a larger area, while a narrow angle spread limits the coverage area. Satellite communication systems typically use antennas with wide angle spreads to provide broad coverage.

Direction Finding

Direction finding is the process of determining the direction of a signal source. Angle spread is important in direction finding because it affects the accuracy and resolution of the direction-finding system. Direction-finding systems typically use antennas with narrow angle spreads to improve accuracy and resolution.

Conclusion

Angle spread is an important parameter in radio communication and radar systems. It is a measure of the angular extent of a signal's energy distribution and is determined by the physical characteristics of the transmitting and receiving antennas, as well as the wavelength and bandwidth of the signal. Angle spread is important in determining the accuracy, resolution, and coverage area of radio communication and radar systems. By understanding angle spread, engineers can design more effective and efficient radio communication and radar systems.