How does an Antenna work? | ICT #4

Summary

This video explains the science behind antennas, covering how they convert electric signals to electromagnetic waves and vice versa. It explores the physics of wave separation using oscillating charges and delves into how antennas like dipole and Yagi-Uda types function for transmission and reception. The video also describes modern antennas used in dish TVs and cell phones, such as parabolic reflectors and patch antennas, highlighting their design and function. Viewers gain insight into the practical workings of antennas and their role in telecommunications.

Takeaways

• 📡 Antennas are essential in telecommunications for converting electric signals into electromagnetic waves and vice versa.
• 🔄 A simple closed conductor can produce a fluctuating magnetic field, but it does not propagate signals effectively.
• 🔋 The physics behind antennas involves the oscillation of positive and negative charges, creating a dipole that generates an electric field.
• 🏃‍♂️ The acceleration and deceleration of charged particles affect the electric field, leading to a 'memory effect' that influences wave propagation.
• 🌊 The electric field's variation due to charge movement results in a wavefront that separates and propagates, forming an electromagnetic wave.
• 🌀 The wavelength of the propagated wave is twice the length of the dipole, which is a critical factor in antenna design.
• 🔌 A practical antenna can be made by oscillating positive and negative charges, such as applying a time-varying voltage to a conducting rod.
• 📶 The length of an antenna for optimal transmission or reception should be half the wavelength of the signal.
• 🔄 Antennas operate reversibly, functioning as both transmitters and receivers of electromagnetic waves.
• 📺 Practical examples of antennas include Yagi-Uda antennas for TV reception and dish antennas with parabolic reflectors for satellite signals.
• 📱 Modern devices like cell phones use patch antennas, which are composed of a metallic patch, a ground plane, and a dielectric material.

Q & A

What is the primary function of an antenna?

An antenna's primary function is to receive an electromagnetic wave and convert it into an electric signal, or to receive an electric signal and radiate it as an electromagnetic wave.

How does an antenna convert an electric signal into an electromagnetic wave?

An antenna converts an electric signal into an electromagnetic wave by utilizing the principle of electromagnetic induction with a closed conductor, which produces a fluctuating magnetic field and an electric field around it.

Why doesn't the fluctuating field around the source transmit signals?

The fluctuating field around the source does not propagate and is of no use in transmitting signals because it merely fluctuates around the source without moving away from it.

What is a dipole and how is it related to antenna function?

A dipole is an arrangement of one positive and one negative charge placed a distance apart. It is related to antenna function because the oscillation of these charges produces a varying electric field that can propagate as an electromagnetic wave.

What is the 'memory effect' of the electric field mentioned in the script?

The 'memory effect' of the electric field refers to the phenomenon where the electric field does not immediately adjust to new conditions when charges are accelerating or decelerating, causing the field to stretch and deform.

How does the wavelength of the propagated wave relate to the length of the dipole?

The wavelength of the propagated wave is exactly double the length of the dipole, as observed in the analysis of the electric field intensity variation with distance.

What is the practical arrangement for oscillating positive and negative charges in an antenna?

A practical arrangement for oscillating positive and negative charges in an antenna involves taking a conducting rod with a bend in its center and applying a time-varying voltage signal at the center.

What is the ideal length of an antenna for perfect transmission?

For perfect transmission, the ideal length of an antenna should be half of the wavelength of the signal it is designed to transmit.

Can an antenna also function as a receiver? How does it work?

Yes, an antenna can function as a receiver. When a propagating electromagnetic field hits the antenna, it induces a varying charge accumulation, which in turn produces a varying electric voltage signal at the center of the antenna.

What are the main components of a dish TV antenna?

The main components of a dish TV antenna are a parabolic shaped reflector and a low-noise block downconverter (LNBF), which includes a feedhorn, waveguide, PCB, and probe.

How does a patch antenna in a cell phone work?

A patch antenna in a cell phone consists of a metallic patch or strip placed on a ground plane with a dielectric material in between. The metallic patch acts as a radiating element and should be half the wavelength for proper transmission and reception.

Outlines

00:00

📡 Understanding Antennas: Conversion of Electric Signals to EM Waves

This paragraph introduces the fundamental concept of antennas in telecommunications, explaining their role in converting electric signals to electromagnetic waves and vice versa. It discusses the science behind antennas, emphasizing the need for electromagnetic waves to propagate away from the source rather than just fluctuating around it. The physics of wave separation is introduced through the example of a dipole, where oscillating charges create a varying electric field. The concept of 'memory effect' in the electric field due to accelerating or decelerating charges is highlighted, which leads to the formation and propagation of electromagnetic waves. The paragraph concludes with a practical example of creating an antenna by applying a time-varying voltage signal to a conducting rod, which results in wave propagation similar to the dipole case.

05:00

📺 Practical Antennas: From Dipole to Patch Antennas

The second paragraph delves into practical applications of antennas, starting with the dipole antenna used for TV reception. It describes the Yagi-Uda antenna, which includes a dipole, reflector, and director to focus signals. The operation of dish TV antennas is explained, detailing how the parabolic dish focuses signals onto the low-noise block downconverter (LNBF). The LNBF's components and their role in signal processing are outlined, including the feedhorn, waveguide, PCB, and probe. The paragraph also discusses the polarization of signals and the use of two probes in an LNB to detect both horizontally and vertically polarized signals. Finally, it touches on the patch antenna used in cell phones, which consists of a metallic patch on a ground plane with a dielectric material in between, emphasizing the importance of the patch's length for proper transmission and reception.

Keywords

💡Antennas

Antennas are devices used in telecommunications to transmit and receive radio waves. They are essential for the functioning of various communication systems. In the video, antennas are described as converting electric signals into electromagnetic waves and vice versa. This conversion process is central to the video's theme of explaining how antennas work.

💡Electromagnetic Waves

Electromagnetic waves are disturbances in the electromagnetic field that travel through space. They are generated by oscillating charges and are the medium through which antennas transmit signals. The video explains how antennas separate these waves from their source and propagate them, which is crucial for signal transmission.

💡Electric Signal

An electric signal is a variation of voltage or current in an electrical circuit. In the context of the video, electric signals are the input to antennas, which then convert them into electromagnetic waves for transmission. The conversion process is a key part of the antenna's function.

💡Dipole

A dipole refers to a pair of equal and opposite charges separated by a distance. In antennas, a dipole configuration is used to create an oscillating electric field that generates electromagnetic waves. The video uses the dipole as an example to illustrate the physics behind wave separation in antennas.

💡Oscillating Charges

Oscillating charges refer to charged particles that move back and forth, creating a varying electric field. This is a fundamental concept in the video, as the oscillation of charges is what enables antennas to generate electromagnetic waves for signal transmission.

💡Wavefront

A wavefront is a surface of continuous phase of a wave that propagates through space. The video describes how the wavefront formed by oscillating charges expands and deforms, eventually leading to the propagation of electromagnetic waves, which is a critical step in the antenna's operation.

💡Memory Effect

The memory effect in the context of the video refers to the property of an electric field produced by accelerating or decelerating charges to retain its shape even as the charges continue to move. This effect is important for understanding how the electric field lines deform and propagate as waves.

💡Wavelength

Wavelength is the physical length of one complete cycle of an electromagnetic wave. The video explains that the wavelength of the wave produced by an antenna is twice the length of the dipole, which is a key relationship in antenna design.

💡Yagi-Uda Antenna

The Yagi-Uda antenna is a type of directional antenna often used for TV reception. In the video, it is mentioned as an example of a practical antenna that uses a dipole, reflector, and director to focus signals. This illustrates how the principles discussed are applied in real-world antenna designs.

💡Parabolic Dish Antenna

A parabolic dish antenna is a type of antenna that uses a parabolic reflector to focus incoming signals onto a feed point. The video describes how this type of antenna, along with a low-noise block downconverter (LNB), is used in satellite communication systems.

💡Patch Antenna

A patch antenna is a type of antenna used in mobile devices like cell phones. It consists of a metallic patch placed on a ground plane with a dielectric material in between. The video mentions that the length of the metal patch should be half of the wavelength for proper transmission and reception, demonstrating its application in modern communication devices.

Highlights

Antennas convert electromagnetic waves to electric signals and vice versa.

Antennas require separation of electromagnetic waves from the source for propagation.

A dipole arrangement of charges produces an electric field.

Oscillating charges create a varying electric field due to acceleration and deceleration.

The electric field has a 'memory effect' that affects how it adjusts to new conditions.

The varying electric field generates a varying magnetic field perpendicular to it.

Wave propagation is sinusoidal in nature.

The wavelength of the propagation is double the length of the dipole.

An antenna can be made by oscillating positive and negative charges.

A conducting rod with a bend can be used to create an oscillating charge.

The frequency of the transmitted signal matches the frequency of the applied voltage signal.

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

Antennas can operate as receivers when hit by a propagating electromagnetic field.

The operation of an antenna is reversible, allowing it to work both as a transmitter and a receiver.

Practical antennas like the Yagi-Uda antenna use a dipole for signal reception.

Dish TV antennas use a parabolic reflector and a low-noise block downconverter.

The LNBF in dish antennas processes signals such as filtration and frequency conversion.

Cell phones use patch antennas, which consist of a metallic patch on a ground plane.

The length of the metal patch in a patch antenna should be half of the wavelength.

Transcripts

- [Narrator] Antennas are widely used

in the field of telecommunications,

and we have already seen many applications for them

in this video series.

Antennas receive an electromagnetic wave

and convert it to an electric signal,

or receive an electric signal

and radiate it as an electromagnetic wave.

In this video, we are going to look at the science

behind antennas.

We have an electric signal,

so how do we convert it to an electromagnetic wave?

You might have a simple answer in your mind.

That is to use a closed conductor

and with the help of the principle

of electromagnetic induction,

you will be able to produce a fluctuating magnetic field

and an electric field around it.

However, this fluctuating field around the source

is of no use in transmitting signals.

The electromagnetic field here does not propagate,

instead, it just fluctuates around the source.

In an antenna, the electromagnetic waves

need to be separated from the source

and they should propagate.

Before looking at how an antenna is made,

let's understand the physics behind the wave separation.

Consider one positive and one negative charge

placed a distance apart.

This arrangement is known as a dipole,

and they obviously produce an electric field as shown.

Now, assume that these charges are oscillating as shown,

at the midpoint of their path,

the velocity will be at the maximum

and at the ends of their paths the velocity will be zero.

The charged particles undergo continuous acceleration

and deceleration due to this velocity variation.

The challenge now is to find out

how the electric field varies due to this movement.

Let's concentrate on only one electric field line.

The wavefront formed at time zero

expands and is deformed as shown

after one eighth of a time period.

This is surprising.

You might've expected a simple electric field as shown

at this location.

Why has the electric field stretched

and formed a field like this?

This is because the accelerating

or decelerating charges produce an electric field

with some memory effects.

The old electric field does not easily adjust

to the new condition.

We need to spend some time to understand this memory effect

of the electric field or kink generation of accelerating

or decelerating charges.

We will discuss this interesting topic in more detail

in a separate video.

If we continue our analysis in the same manner,

we can see that at one quarter of a time period,

the wavefront ends meet at a single point.

After this, the separation

and propagation of the Wavefront happens.

Please note that this varying electric field

will automatically generate a varying magnetic field

perpendicular to it.

If you draw electric field intensity variation

with the distance, you can see that the wave propagation

is sinusoidal in nature.

It is interesting to note

that the wavelength of the propagation so produced

is exactly double that of the length of the dipole.

We will come back to this point later.

This is exactly what we need in an antenna.

In short, we can make an antenna

if we can make an arrangement for oscillating the positive

and negative charges.

In practice, the production of such an oscillating charge,

is very easy.

Take a conducting rod with a bend in its center,

and apply a voltage signal at the center.

Assume this is the signal you have applied,

a time-varying voltage signal.

Consider the case at time zero.

Due to the effect of the voltage,

the electrons will be displaced from the right of the dipole

and will be accumulated on the left.

This means the other end which has lost electrons

automatically becomes positively charged.

This arrangement has created the same effect

as the previous dipole charge case,

that is positive and negative charges at the end of a wire.

With the variation of voltage with time,

the positive and negative charges will shuttle to and fro.

The simple dipole antenna also produces the same phenomenon

we saw in the previous section and wave propagation occurs.

We have now seen how the antenna works as a transmitter.

The frequency of the transmitted signal

will be the same as the frequency

of the applied voltage signal.

Since the propagation travels at the speed of light,

we can easily calculate the wavelength of the propagation.

For perfect transmission,

the length of the antenna should be half of the wavelength.

The operation of the antenna is reversible

and it can work as a receiver

if a propagating electromagnetic field hits it.

Let's see this phenomenon in detail.

Take the same antenna again and apply an electric field.

At this instant, the electrons

will accumulate at one end of the rod.

This is the same as an electric dipole.

As the applied electric field varies,

the positive and negative charges

accumulate at the other ends.

The varying charge accumulation

means a varying electric voltage signal

is produced at the center of the antenna.

This voltage signal is the output

when the antenna works as a receiver.

The frequency of the output voltage signal

is the same as the frequency of the receiving EM wave.

It is clear from the electric field configuration

that for perfect reception,

the size of the antenna should be half of the wavelength.

In all these discussions,

we have seen that the antenna is an open circuit.

Now let's see a few practical antennas and how they work.

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

The colored bar acts as a dipole and receives the signal.

A reflector and director

are also needed in this kind of antenna

to focus the signal on the dipole.

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

The dipole antenna converted the received signal

into electrical signals, and these electrical signals

were carried by coaxial cable to the television unit.

Nowadays we have moved to dish TV antennas.

These consists of two main components,

a parabolic shaped reflector

and the low-noise block downconverter.

The parabolic dish receives electromagnetic signals

from the satellite and focuses them onto the LNBF.

The shape of the parabolic is very specifically

and accurately designed.

The LNBF is made up of a feedhorn,

a waveguide, a PCB, and a probe.

In this animation, you can see how the incoming signals

are focused onto the probe via the feedhorn and waveguide.

At the probe, voltage is induced

as we saw in the simple dipole case.

The voltage signal so generated is fed to a PCB

for signal processing such as filtration,

conversion from high to low frequency and amplification.

After signal processing, these electrical signals

are carried down to the television unit

through a coaxial cable.

If you open up an LNB,

you will most probably find two probes instead of one.

The second probe being perpendicular to the first one.

The two probe arrangement means the available spectrum

can be used twice

by sending the waves with either horizontal

or vertical polarization.

One probe detects the horizontally polarized signal

and the other, the vertically polarized signal.

The cell phone in your hand

uses a completely different type of antenna

called a patch antenna.

A patch antenna consists of a metallic patch or strip

placed on a ground plane

with a piece of dielectric material in between.

Here, the metallic patch acts as a radiating element.

The length of the metal patch

should be half of the wavelength

for proper transmission and reception.

Please note that the description of the patch antenna

we explained here is very basic.

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