How does an Antenna work? | ICT #4

Introduction to Antennas

In this section, we will explore the science behind antennas and how they work in telecommunications.

The Principle of Electromagnetic Induction

• Antennas receive electromagnetic waves and convert them into electric signals or vice versa.

• To convert an electric signal into an electromagnetic wave, a closed conductor can be used with the principle of electromagnetic induction. This creates a fluctuating magnetic field and an electric field around it.

• However, this fluctuating field does not propagate and is of no use in transmitting signals.

Wave Separation in Antennas

• In order for antennas to transmit signals, the electromagnetic waves need to be separated from the source and propagate.

• Understanding the physics behind wave separation is crucial before delving into antenna construction.

Dipole Arrangement

• Consider two charges placed a distance apart, known as a dipole. They produce an electric field.

• When these charges oscillate, they undergo continuous acceleration and deceleration due to velocity variation.

• The resulting electric field varies due to this movement, forming wavefronts that expand and deform over time.

Memory Effect of Electric Field

• The accelerating or decelerating charges generate an electric field with memory effects. The old electric field does not easily adjust to the new condition.

• This memory effect leads to kink generation and affects the shape of the electric field.

Propagation of Wavefronts

• Analyzing further, at one-quarter of a time period, wavefront ends meet at a single point before separating again.

• This varying electric field automatically generates a varying magnetic field perpendicular to it.

• The propagation of these wavefronts is sinusoidal in nature with a wavelength exactly double that of the length of the dipole.

Creating an Antenna

This section explains how to create an antenna by arranging oscillating positive and negative charges.

Oscillating Charge Arrangement

• An antenna can be made by arranging for the oscillation of positive and negative charges.

• Practically, this is achieved by taking a conducting rod with a bend in its center and applying a time-varying voltage signal at the center.

Transmission Function of Antennas

• The simple dipole antenna produces wave propagation similar to the previous section.

• The frequency of the transmitted signal is the same as the frequency of the applied voltage signal.

• The wavelength of propagation can be calculated based on the speed of light.

Length Requirement for Perfect Transmission

• For perfect transmission, the length of the antenna should be half of the wavelength.

Antennas as Receivers

This section explores how antennas can also function as receivers when hit by a propagating electromagnetic field.

Reversibility of Antennas

• Antennas can work as receivers if a propagating electromagnetic field hits them.

• When an electric field is applied, electrons accumulate at one end, creating an electric dipole.

• As the applied electric field varies, positive and negative charges accumulate at different ends, resulting in a varying electric voltage signal at the center of the antenna.

Conclusion

Antennas play a crucial role in telecommunications by receiving and transmitting electromagnetic waves. By understanding wave separation and creating arrangements for oscillating charges, antennas can effectively transmit signals. Additionally, antennas can also function as receivers when hit by propagating electromagnetic fields.

New Section

In this section, the speaker discusses the ideal size of an antenna for perfect reception and introduces the concept of an open circuit antenna.

Antenna Size and Configuration

• The size of the antenna should be half of the wavelength for optimal reception.

• The electric field configuration plays a crucial role in determining the antenna size.

• An open circuit antenna is used for reception.

Practical Antennas

This section explores different practical antennas and their functioning.

Dipole Antennas

• In the past, dipole antennas were commonly used for TV reception.

• A dipole antenna consists of a colored bar that acts as a receiver.

• Additional components like reflectors and directors are required to focus the signal on the dipole.

• This complete structure is known as a Yagi-Uda antenna.

• Coaxial cables are used to carry electrical signals from the dipole to the television unit.

Dish TV Antennas

• Dish TV antennas have become popular nowadays.

• They consist of a parabolic-shaped reflector and a low-noise block downconverter (LNBF).

• The parabolic dish receives electromagnetic signals from satellites and focuses them onto the LNBF.

• The shape of the parabolic dish is precisely designed for optimal performance.

• The LNBF includes components like feedhorn, waveguide, PCB, and probe.

• Incoming signals are focused onto the probe via feedhorn and waveguide, inducing voltage in it.

• Signal processing such as filtration, frequency conversion, and amplification takes place on a PCB.

• Electrical signals are then transmitted to the television unit through coaxial cables.

Patch Antennas

This section introduces patch antennas and explains their basic structure.

Patch Antenna Structure

• Patch antennas are a different type of antenna used in devices like cell phones.

• They consist of a metallic patch or strip placed on a ground plane with a dielectric material in between.

• The metallic patch acts as the radiating element.

• The length of the metal patch should be half of the wavelength for proper transmission and reception.

Please note that the description provided here for patch antennas is basic.