Radiation mechanism in dipole

Radiation mechanism in dipole:
Consider a small dipole antenna where the time of travel is negligible.

fig 1a. at a quarter -wavelength
1b. at half-wavelength(opposite charges)
1c. at half-wavelength (no charge on the conductor)

Consider that a small dipole is center-fed in the first quarter of the period T i.e.,  t=T/4 , at this time the charge attains maximum value. At this instant,  the lines travel radially outwards at a distance of .  Assume that the number of lines produced is three as shown in fig., 1a above

Now in the next quarter period of time, three lines produced originally, travel an additional distance of   .  So the total distance becomes   . The charge density on the conductor starts diminishing as the opposite charges are introduced. These opposite charges neutralize the charges on the conductor and they also produce three lines of force which travel a distance of     during the second quarter of the first half. The lines of force produced by the opposite charges are as shown by the dashed lines as shown above in fig., 1b

As compared with the lines of force in the first quarter of the first half, the direction of lines of force is opposite (i.e., upwards) as they are produced by opposite charges. As a result, the appearance of the three lines of force directing upwards in the first   distance while three more lines of force directing downwards in the next   distance. Now there is no charge on the conductor, the lines of force get detached from conductors and combine to form closed loops as shown in fig., 1c above.

It is obvious that in the second half of the period the same procedure is carried out but in the opposite direction. The process is then repeated and carried out indefinitely.

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I have created this blog for educational purposes, so for that, I have written the content by referring many books, web pages. I have also uploaded google images for a better understanding of the concept and I would also like to inform you that I am not responsible for the ads which are being posted on my blog.

Radiation mechanism in 2 wires

Radiation mechanism in 2 wire antenna:
Consider an antenna drives by a transmission line with a voltage source conductor. The electric lines of force are tangent to the electric field. The strength of electric lines of force is proportional to electric field intensity. As the free electrons have a tendency to get separated from the atom, the electric lines of force operate on free electrons of each conductor and force to displace. Due to the charge movement, the current is produced and it produces magnetic field intensity.
The electric field lines travel from positive charges to negative charges while the magnetic field lines form closed loops encircling current-carrying conductors. The charge distribution is due to electric field lines. Assuming a sinusoidal source between the two conductors, the electric field between the conductor is also sinusoidal.

fig., radiation from two-wire antennas
a. antenna and electric field lines
b. antenna and free-space wave

Disclaimer:

I have created this blog for educational purposes, so for that, I have written the content by referring many books, web pages. I have also uploaded google images for a better understanding of the concept and I would also like to inform you that I am not responsible for the ads which are being posted on my blog.

Radiation mechanism in single-wire antennas

Radiation mechanism:

When transmitting and receiving antenna is excited with an alternating voltage, then the initial move will be started by the balanced motion of charges in the antenna. Resonant oscillations are produced by the supplied energy.

Electric and magnetic fields are generated due to sudden changes in charge. When the charges around the antenna are set in motion. The disturbance is spread from the antenna into space. The electric and magnetic fields so produced are perpendicular to each other in space. EM waves don't have boundaries. EM wave energy decreases as it propagates.

Radiation mechanism in single-wire:

It is a fundamental single wire antenna. By the principle of radiation, the current must be time-varying.

For a single wire antenna:

• If the charge is stationary, no current is developed. So no radiation is observed.
• If the charge is moving with uniform velocity, then : 

       i) No radiation occur for a straight wire which is infinity in extent

       ii) Radiation is possible only if the wire is curved; bent, discontinuous, terminated or truncated.

When a wire is energized using a source, the free electrons in wire are set into motion due to the force of electrical lines.

The charges will be accelerated at the source end while they are decelerated due to the reflection at the other end. As a result, radiation fields are created not only at the two ends but also along the remaining part of the wire.

If the pulses of charge traveling along the wire are narrow, then radiation is stronger with a wide frequency spectrum. But if the charge is oscillating, then the radiation of a single frequency is produced.

fig., different wire configurations producing radiation

Disclaimer:

I have created this blog for educational purposes, so for that, I have written the content by referring many books, web pages. I have also uploaded google images for a better understanding of the concept and I would also like to inform you that I am not responsible for the ads which are being posted on my blog.

Basic antenna elements

Basic antenna elements:

The basic antenna elements are five in number. They are:

1.Alternating current element or Hertzian dipole

2.Short dipole

3.Short monopole

4.Half-wave dipole

5.Quarter-wave monopole

1. Alternating current element or Hertzian dipole:

It is a short linear antenna in which the current along its length is assumed to be constant.

2.Short dipole:

It is a linear antenna whose length is less than    and the current distribution is assumed to be triangular.

3.Short monopole:

It is a linear antenna whose length is less than    and the current distribution is assumed to be triangular.

4.Half-wave dipole:

It is a linear antenna whose length is    and the current distribution is assumed to be sinusoidal. It is usually center-fed.

5.Quarter-wave monopole:

It is a linear antenna whose length is     and the current distribution is assumed to be sinusoidal. It is fed at one end with respect to earth.

Disclaimer:

I have created this blog for educational purposes, so for that, I have written the content by referring many books, web pages. I have also uploaded google images for a better understanding of the concept and I would also like to inform you that I am not responsible for the ads which are being posted on my blog.

Definitions and functions of antennas

Definitions of Antennas:

The following are the definitions of antennas:

Definition 1: The basic definition of an antenna is, it is a metallic device in the form of either wire or rod used for radiating or receiving radio waves.

Definition 2: According to the IEEE standards definition of terms of the antenna, an antenna is aerial and is the means for radiating or receiving radio waves.

Definition 3: The antenna produces electromagnetic fields and these fields constitute electromagnetic waves. Thus antenna can be defined as the source or radiator of electromagnetic waves.

Definition 4: An antenna can be used to sense the electromagnetic waves. Hence it can be defined as a sensor of electromagnetic waves.

Definition 5: An antenna can be defined as a transducer that converts radio frequency electrical current into an electromagnetic wave of the same frequency as that of an electrical current.

Definition 6: An antenna act as a coupling device between a generator or transmitter and free space. Hence antenna is an impedance matching device between free space and transmitter line.

Properties of Antennas:

Irrespective of the types of antenna, every antenna possesses similar properties:

1.Equality of impedance:

An antenna should have equal impedance. That means the impedance for transmitting must be equal to the impedance of receiving. This property is called equality of impedance.

2.Equality of directional patterns:

An antenna exhibits identical directional pattern whether it is used for transmitting or receiving purposes. This property is known as equality of directional pattern.

3.Equality of effective length:

An antenna's effective length should be the same for the transmission as well as for the reception.

Disclaimer:
I have created this blog for educational purposes, so for that, I have written the content by referring many books, web pages. I have also uploaded google images for a better understanding of the concept and I would also like to inform you that I am not responsible for the ads which are being posted on my blog.

Introduction to the antennas

Antenna:

The antenna is an electrical conductor or system of conductors. These antennas are the basic components of any electric system and are connecting links between the transmitters and free space or free space and the receiver.

Antennas are of two types:

1.Transmitting antenna

2.Receiving antenna

Note:

In two-way communication, the same antenna can be used as a transmitter and as a receiver. This type of antenna is known as a transceiver.

fig., antenna

Functions of an Antenna:

1. It is used as a transducer.

2. It is used as an impedance matching device.

3. It is used to direct the radiated energy in desired directions and to suppress it in unwanted directions.

4. It is used to sense the presence of electromagnetic waves.

5. It is used as a temperature sensor.

Disclaimer:
I have created this blog for educational purposes, so for that, I have written the content by referring many books, web pages. I have also uploaded google images for a better understanding of the concept and I would also like to inform you that I am not responsible for the ads which are being posted on my blog.