How do RF Antenna Works – Simple Explanation

Today we use more and more devices that require an antenna. Antennas are used for a variety of devices including televisions, radios, cell phones, and computers. RF antennas are also used in wireless technology like Wi-Fi, Bluetooth, and GPS.

An antenna is a piece of metal or other conductive material designed to transmit or receive signals from or to a radio or other device. An antenna is basically a transducer that converts electrical signals into radio waves and vice versa. They are also called radio antennas or RF antennas.

History of Electromagnetic Waves

Famous mathematician James Clerk Maxwell was the first person who laid the foundation for electromagnetism. He has formulated the mathematical equations which are still considered the basis of electromagnetism.

Heinrich Hertz, one of the great scientists of the 19th century is the first man to transmit electromagnetic waves and detect them. In his experiment, high voltage current was applied to the ends of metal wires which produced a spark between the gaps between the wires. These sparks caused electromagnetic radiation to its surroundings and resulted in a spark between a metal coil which was located approximately one meter from the transmitter. This was the first successful demonstration of electromagnetic wave transmission and receiving.

How do antennas radiate radio waves?

A dipole antenna is one of the simplest antennas which accommodate half a wavelength of the signal it radiates. Let’s consider the case of an oscillating electric dipole. When the signal is applied, the charges will be continuously oscillating according to the signal frequency. 

The velocity of the charge at both ends will be zero and maximum at the midpoint due to continuous acceleration and deceleration of charges.

Let’s consider one of the electric field lines. When the velocity of the charges changes, the electric field line deforms (it does not gain the changing shape). The deformation is due to acceleration and deceleration of the charges causing KINKs in the electric field.

It means that the old electric field does not get adjusted to the new electric field as the charges continuously change. This deformation continues as the acceleration and deceleration of the charges in the dipole continue.

When the two charges meet at the center point, the deformed electric field line meets the center point and detaches and radiates (when the charges meet at a central point and rotate polarity).

These varying electric filed at the dipole creates a varying magnetic field perpendicular to each other (90 Degree). As the varying polarity at the dipole continuously changes according to the signal fed to the antenna, electromagnetic waves are generated and transmitted from the dipole. This is the basics of signal radiation from an RF antenna.

Size, shape, and material used in antenna design vary based on the frequency, power, and applications they are used for.

What is the Gain of an antenna?

The gain of an antenna is its sensitivity to a given radio frequency (or frequency range). Gain is measured in decibels (dB). To calculate the gain of an antenna, you must know its power rating, frequency, and distance from the antenna. Gain is one of the significant specifications of an antenna that qualifies it for efficient transmission and reception of radio waves.

Example: GPS signal received on any device would be less than -125dBm (0.1fwatts). The sensitivity of the GPS antenna should be high for better signal reception.  

What is the difference between antennas as a transmitter/receivers?

Antennas are used to transmit signals, and they are also used in a wide range of applications, including televisions, radio, and cell phones. Antennas used in transmission are usually designed to handle high power and are well-matched (impedance matching) for maximum efficiency.

Example: Cell base station antennas typically transmit RF waves at a peak power of 46dBm (40 Watts).

An antenna in the receiver collects electromagnetic waves and converts them into electrical signals. These low-power signals are amplified and demodulated to convert into meaningful information in the forms of data, video, or audio formats. Antennas in the receivers usually have higher sensitivity and are designed to handle low power levels. Example:  Bluetooth antenna typically receives a signal from transmitting devices at approximately -70dBm to -84dBm.

Reference: How does an antenna work

Image source: How does an Antenna work – Lesics youtube channel