Directionality refers to the property of an antenna or a sound source to focus its energy in a particular direction or to receive energy predominantly from a specific direction. It describes how different frequencies are emitted from or received by the antenna or source in various directions.
In terms of antennas:
- Omni-directional (or non-directional) antennas: These types of antennas send or receive signals in all horizontal directions equally. Their radiation patterns are typically doughnut-shaped. They are used where a broad coverage is required. Examples include the antennas used for Wi-Fi routers and mobile communications.
- Directional antennas: These antennas send or receive signals predominantly in one direction. Their radiation patterns may resemble a beam. They are useful for point-to-point communication or when you want to focus your transmission power in one direction. Satellite dishes and TV antennas are common examples.
- Highly-directional antennas: These are extreme versions of directional antennas, focusing energy in a very narrow beam. They can achieve very long communication distances. Parabolic dishes and Yagi antennas are examples.
In terms of acoustics:
- Omni-directional microphones: These pick up sound equally from all directions.
- Uni-directional microphones: These pick up sound predominantly from one direction, which makes them great for isolating a sound source in a noisy environment.
- Bi-directional microphones: These pick up sound from two opposite directions.
The directionality of an antenna or microphone is usually represented graphically in a radiation or polar pattern. The pattern offers a visualization of where the energy is radiated or from where the energy is received.
Directionality is crucial in both antennas and acoustics to ensure the desired coverage or reception and to minimize interference from unwanted sources.