Antenna gain is an important metric that measures the antenna's ability to focus input power into a specific direction. Specifically, it refers to the ratio of the power density of the signal generated by a real antenna to that of an ideal isotropic point-source antenna at the same location in space, with equal input power. In simpler terms, it describes the antenna's ability to amplify signals, indicating how efficiently the antenna radiates or receives signals in a particular direction.
Principle of Gain:
An antenna converts input electrical signals into electromagnetic waves and radiates them into space through its design and structure. Antennas with higher gain can focus more energy in a specific direction, increasing the signal strength in that direction. Conversely, antennas with lower gain radiate energy more evenly in all directions, resulting in weaker signal strength in specific directions.
For example, a parabolic antenna works by reflecting spherical waves from a feed located at its focus and converging them into plane waves, thereby increasing the energy in the desired direction and achieving higher gain.
Factors Influencing Gain:
· Antenna Size and Shape: Generally, larger antennas can collect and radiate more energy, resulting in higher gain. For instance, large parabolic antennas typically have higher gain than smaller whip antennas.
· Operating Frequency: At the same antenna structure, higher frequencies (with shorter wavelengths) often allow for a larger relative antenna size, potentially increasing gain. For example, antennas operating in the millimeter-wave frequency band can achieve higher gain at smaller physical sizes due to their short wavelengths.
· Materials and Manufacturing Process: High-quality materials and precise manufacturing can reduce signal loss within the antenna, improving radiation efficiency and increasing gain.
The Impact of Gain on Antennas:
Communication Range:
High Gain: Higher gain antennas can transmit signals over longer distances. For instance, in long-range wireless communications, high-gain antennas can transmit signals over several kilometers or more. In mountainous areas, using high-gain antennas on wireless base stations can extend coverage to more remote villages, ensuring communication.
Low Gain: The signal propagation range is limited. With the same transmission power, low-gain antennas may only cover a few hundred meters. For example, if a home Wi-Fi router uses a low-gain antenna, it may struggle to provide coverage in larger areas with many rooms, leaving certain areas with weak or no signal.
Signal Strength and Quality:
High Gain: High gain can enhance signal strength in a specific direction, making the received signal clearer, more stable, and reducing the error rate. In satellite communication, ground stations use high-gain antennas to better receive weak signals from satellites, ensuring communication quality.
Low Gain: Low gain results in weaker signal strength, making the signal more susceptible to interference and noise, which can degrade signal quality and cause issues like lag or dropped connections. For example, walkie-talkies with low-gain antennas in a city environment with tall buildings may experience signal degradation due to obstruction and reflection from buildings.
Coverage Area:
High Gain: In directional antennas, high gain results in a narrower beam, concentrating energy in a specific direction, enabling longer-range coverage in that direction but with a limited coverage angle. For example, high-gain directional antennas in radar systems can detect targets at long distances in specific directions, but their scanning angles are narrow.
Low Gain: Low gain antennas typically have a wider beam, offering broader coverage, but the signal distance may be shorter. For instance, home routers with omnidirectional low-gain antennas can provide coverage over a wider area, allowing devices in various directions to receive the signal.
Interference Resistance:
High Gain: With energy concentrated in a specific direction, high-gain antennas can better resist interference from signals coming from other directions. In military communications, high-gain antennas help focus the beam on a target direction, reducing the impact of interference from other directions and improving communication confidentiality and reliability.
Low Gain: With more dispersed energy, low-gain antennas are more vulnerable to interference from various directions, making them less resistant to disruptions in complex electromagnetic environments.
