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TRANSMISSION LINE PRESENTATION ON-www.engineersportal.inINDEXINTRODUCTIONTYPES OF TRANSMISSION LINELOSSES OF TRANSMISSION LINEAPPLICATIONPRINCIPLE OF TRANSMISSION LINEFOUR TERMINAL MODEL STANDING WAVEREFERENCECONCLUSIONwww.engineersportal.in

INTRODUCTIONA TRANSMISSION LINE is a device designed to guide electrical energy from one point to another. It is used, for example, to transfer the output rf energy of a transmitter to an antenna. This energy will not travel through normal electrical wire without great losses. Although the antenna can be connected directly to the transmitter, the antenna is usually located some distance away from the transmitter. On board ship, the transmitter is located inside a radio room and its associated antenna is mounted on a mast. A transmission line is used to connect the transmitter and the antenna

www.engineersportal.in3PRINCIPLE OF TRANSMISSION LINEAll transmission lines have two ends . The end of a line connected to a source is ordinarily called the INPUT END or the GENERATOR END. Other names given to this end are TRANSMITTER END, SENDING END, and SOURCE. The other end of the line is called the OUTPUT END or RECEIVING END. Other names given to the output end are LOAD END and SINK.

The ratio of voltage to current (Ein/Iin) at the input end is known as the INPUT IMPEDANCE (Zin). This is the impedance presented to the transmitter by the transmission line and its load, the antenna. The ratio of voltage to current at the output (E out/Iout) end is known as the OUTPUT IMPEDANCE (Zout). This is the impedance presented to the load by the transmission line and its source. If an infinitely long transmission line could be used, the ratio of voltage to current at any point on that transmission line would be some particular value of impedance. This impedance is known as the CHARACTERISTIC IMPEDANCE

www.engineersportal.in FOUR TERMINAL MODEL OF A TRANSMISSION LINEFor the purposes of analysis, an electrical transmission line can be modelled as a two-port network (also called a quadrupole network), as follows:

In the simplest case, the network is assumed to be linear (i.e. the complex voltage across either port is proportional to the complex current flowing into it when there are no reflections), and the two ports are assumed to be interchangeable. If the transmission line is uniform along its length, then its behaviour is largely described by a single parameter called the characteristic impedance, symbol Z0

www.engineersportal.in5TYPES OF TRANSMISSION LINEBALANCED TWO WIRE CO AXIAL CABLEWAVE GUIDEMICROSTRIPFIBER OPTICS

www.engineersportal.in1.BALANCED TWO WIREIn this type of construction for two wire transmission lines the insulated spacers are used in order to maintain the distance between the transmission lines or between the two conducting wire equally throughout

MERITSThere are the following merits of balance two wire lines.1. The cost of two wire transmission line is very low as compared to other types of lines.2. To design the open two line transmission line is quite simple and easy too.3. Open two wire lines are capable of handling high power.DEMERITS1. It cannot be used on very high frequencies because it will generate skin effect.

www.engineersportal.in 2 CO-AXIAL CABLEAs shown in the given diagram the co-axial cable consists of inner conducting wire made of copper, over this conducting wire the coating of polyethylene or taplon material is carried out. Then it is enclosed in the braded wire in the shape of mash. The outer surface of this wire is enclosed in a plastic jacket.

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MERITSThere are the following merits of co-axial cable. 1. As the outer conductor (braded wire) is grounded, therefore the possibility of external interference is minimized. The output of the load end will be less noised.2. The co-axial cable is used for high frequencies transmission.3. Co-axial cable occupies less space as compared to two wire lines.

DEMERITS

1. This type of transmission line is costly with respect to two wire lines.2. Designing of co-axial cable is difficult as compared to two wire lines.3. This type of transmission lines handles low power transmissions.

www.engineersportal.in3 WAVE GUIDEA waveguide is a special form of transmission line consisting of a hollow, metal tube. The tube wall provides distributed inductance, while the empty space between the tube walls provide distributed capacitance

Wave guides conduct microwave energy at lower loss than coaxial cables.Waveguides are practical only for signals of extremely high frequency, where the wavelength approaches the cross-sectional dimensions of the waveguide. Below such frequencies, waveguides are useless as electrical transmission lines.

www.engineersportal.in4 MICROSTRIPAs shown in the above diagram the micro strip consists of a conducting plate made of copper which works as an earth plate in the circuit. There is thick coat of insulating material over the copper plate which is made of fiber glass or polystyrene. This insulated plate works as a dielectric in the micro strip line. At the top of the insulated plate one or more than one strips of the best conducting material are plated which is made of gold, aluminum etc.

www.engineersportal.inMERITSThere are the following merits of the micro strip line.1. Very high frequency.2. Small size3. Low weight.4. Losses are minimum.

DEMERITS

1. The cost of micro strip is very high as compared to co-axial and two wire line.2. The micro strip line cannot be used as a transmission line when the distance between source and load is long.3. This type of transmission line cannot be used in twisty paths between source and load.

www.engineersportal.in5 FIBER OPTICS

Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information.

The process of communicating using fiber-optics involves the following basic steps: Creating the optical signal involving the use of a transmitter, relaying the signal along the fiber, ensuring that the signal does not become too distorted or weak, receiving the optical signal, and converting it into an electrical signal.

www.engineersportal.inLOSSES OF TRANSMISSION LINERadiation LossesWhen the high frequency current or voltage wave form flow through the transmission lines, the magnetic field expands and collapse around the transmission lines at the same rate of input frequency. As we know that around the magnetic field there is also an electric field, therefore at high frequency radiation causes the attenuation in the energy provided by the source towards the load.

2. Conductor heatingWhen the current flow takes place through the transmission line, the conducting wires of the line starts to become heat up. This heating of the lines reduces the energy provided by the source to the load.

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3. Dielectric Loss or Heating

As the transmission lines are composed of two parallel conducting wires and current flow take place through the line. The potential difference exists between the two lines. This potential difference causes the leakage current through dielectric. As a result the heating of dielectric material takes place which reduces the energy provided by source to load.www.engineersportal.inSTANDING WAVEWhenever there is a mismatch of impedance between transmission line and load, reflections will occur. If the incident signal is a continuous AC waveform, these reflections will mix with more of the oncoming incident waveform to produce stationary waveforms called standing waves.

www.engineersportal.inAPPLICATION OF TRANSMISSION LINE1.Signal transfer:-Electrical transmission lines are very widely used to transmit high frequency signals over long or short distances with minimum power loss. One familiar example is the down lead from a TV or radio aerial to the receiver.2.Pulse generation:-Electrical transmission lines are very widely used to transmit high frequency signals over long or short distances with minimum power loss. One familiar example is the down lead from a TV or radio aerial to the receiver.These are sometimes used as the pulsed power sources for radar transmitters and other devices.3.Stub filters:-If a short-circuited or open-circuited transmission line is wired in parallel with a line used to transfer signals from point A to point B, then it will function as a filter.www.engineersportal.inCONCLUSIONOur discusion answers the most important questions about the behavior of transmission lines. We show that it is the attenuation of higher frequencies that causes the rounding off of a step-change in voltage, not the dispersion of higher frequencies. Indeed, we show that the dispersion of higher frequencies is such that higher frequencies will arrive sooner than lower frequencies.www.engineersportal.inREFERENCE1.Book of antenna and wave propagation and wireless communication by Jackman, Shawn M.; Matt Swartz, Marcus Burton, Thomas W. Head2.www.ieeexplore paper.com3. Hyeong Tae Jeong, Student Member, IEEE, Ji Eun Kim, Ik Soo Chang, Member, IEEE, and Chul Dong Kim, Member, IEEE4. IEEE paper of Bhavesh R. Bhalja and Rudra Prakash Maheshwari.

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