Short Answer

Radiation from an antenna refers to the electromagnetic waves released into space when electric charges inside the antenna oscillate due to an alternating current (AC). These waves carry energy and information away from the antenna, allowing wireless communication such as radio, TV, mobile signals, and Wi-Fi.

When an antenna radiates, the changing electric and magnetic fields spread outward in all directions or in a specific direction depending on the design. This radiation is essential for transmitting signals over long distances without wires.

Detailed Explanation :

Radiation from an Antenna

Radiation from an antenna is the process by which electromagnetic waves are generated and sent into the surrounding space. These waves are produced when electric charges inside the antenna oscillate back and forth due to an applied alternating current (AC). The acceleration of these charges creates changing electric and magnetic fields, which detach from the antenna and propagate outward as EM waves.

This radiation allows information—such as voice, video, or data—to travel wirelessly over large distances. Antenna radiation is at the heart of all wireless technologies including radio broadcasting, mobile communication, Wi-Fi, satellite links, and radar systems.

How Radiation Is Produced

To understand radiation from an antenna, it is important to know how electric charges behave:

1. Alternating Current (AC) is applied
   • When AC flows through an antenna, electrons move back and forth.
2. Accelerating charges disturb surrounding fields
   • A changing electric field produces a changing magnetic field.
   • A changing magnetic field produces a changing electric field.
3. Fields detach and propagate outward
   • These self-sustaining fields form an electromagnetic wave.
   • The wave moves away from the antenna at the speed of light.

This is the basic mechanism of radiation from any antenna.

The Near Field and Far Field

Radiation around an antenna can be divided into two regions:

1. Near Field Region

• Very close to the antenna
• Fields are strong but do not radiate energy far
• Mainly inductive and reactive fields
• Used in RFID, NFC, wireless chargers

2. Far Field Region

• Starts at several wavelengths away from the antenna
• True electromagnetic radiation exists here
• Energy travels freely into space
• Used for communication signals

Most practical communication systems rely on the far-field radiation.

How Antenna Shape Affects Radiation

The pattern in which an antenna radiates depends on its shape and size.

1. Dipole Antenna

• Radiates in a doughnut-shaped pattern
• Used in radios and TVs

2. Yagi Antenna

• Radiates mainly in one direction
• Used for long-distance TV and communication

3. Dish Antenna (Parabolic)

• Radiates extremely focused beams
• Used for satellite TV, radar, and astronomy

4. Loop Antenna

• Radiates weakly but is compact
• Used in RFID and AM radio

The radiation pattern determines range, direction, and signal strength.

Radiation Pattern

A radiation pattern is a diagram showing how an antenna spreads energy in space. Two main types include:

Omnidirectional Radiation

• Radiates equally in all directions
• Used in mobile towers, Wi-Fi routers

Directional Radiation

• Radiates more energy in a particular direction
• Used in satellite dishes and radar systems

A better radiation pattern improves signal quality and communication efficiency.

Polarization of Radiation

Radiated waves can be polarized based on how the electric field vibrates:

• Vertical polarization
• Horizontal polarization
• Circular polarization

Matching polarization between transmitting and receiving antennas improves performance.

Frequency and Wavelength of Radiated Waves

The frequency of the AC signal determines the frequency of the radiated EM waves. For example:

• 100 MHz AC → FM radio waves
• 2.4 GHz AC → Wi-Fi waves
• 900 MHz AC → Mobile signals

Wavelength affects:

• Antenna size
• Range
• Penetration ability

Higher frequencies produce shorter wavelengths.

Energy Transfer During Radiation

The radiated EM waves carry:

• Energy
• Momentum
• Information (modulated signals)

As the wave travels through space, it spreads out and gradually weakens due to attenuation. However, well-designed antennas minimize loss and improve signal coverage.

Applications of Antenna Radiation

Radiation from an antenna is used in many systems:

1. Radio Broadcasting

AM/FM stations radiate signals to receivers many kilometers away.

2. Television Transmission

TV towers radiate video and audio signals.

3. Mobile Communication

Mobile towers radiate microwave signals for voice calls and internet.

4. Wi-Fi and Bluetooth

Devices communicate using radiated EM waves in GHz frequencies.

5. Satellite Communication

Satellite dishes radiate signals to spacecraft orbiting Earth.

6. Radar

Radar systems radiate microwaves that bounce back from objects.

7. Navigation Systems

GPS satellites radiate signals used for location tracking.

Radiation Efficiency

Antenna radiation efficiency measures how effectively electrical energy is converted into EM waves. Factors affecting efficiency include:

• Material conductivity
• Antenna size
• Frequency
• Losses in nearby objects

High-efficiency antennas radiate more energy and provide better performance.

Safety Aspects of Antenna Radiation

Radiation from communication antennas is non-ionizing and generally safe if exposure is within limits. High-power antennas (like radar) require restricted access for safety. Regulations ensure safe operation in public areas.

Conclusion

Radiation from an antenna is the process of generating and transmitting electromagnetic waves into space through the oscillation of electric charges. These waves carry energy and information and form the foundation of wireless communication systems. The type of radiation depends on frequency, antenna design, and orientation. Understanding antenna radiation is essential for designing efficient communication networks and modern wireless technologies.