Transmission line is defined as the path of carrying alternating electrical energy from source to load.
For example the wire used between T.V antenna and television set or the wire used between transmitter antenna and transmitter are known as transmission lines.
There are the following types of transmission lines.
As shown in the given diagram the two wire transmission lines consists of the figures A,B and C. each construction for the given figure is given as below.
There are the following merits of balance two wire lines.
Zo = 276 log10 2D/d
Here d stands for the diameter of the wire.
D stands for the distance between two wires from its aerials.
Zo stands for characteristics impedance
As 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.
There are the following merits of co-axial cable.
There are the following demerits of the co-axial cable used as transmission line.
Zo = 233 log10 D/d
Where Zo stands for characteristics impedance.
D stands for internal wire diameter of the braded wire.
d stands for diameter of the inner conductor.
A microstrip is simply a copper track running on a side of the PCB while the other side is plain groun plane. The formula will give you the charactersistic impedance of the track, as well as the effective dielectric constant based on the geo-metric parameters. The table provides usual values for 1.6 and 0.8 mm thick PCBs as well as for the standard FR4 substrate or the most advanced Rogers R04003.
As 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.
There are the following merits of the micro strip line.
There are the following demerits of micro strip line.
There are the following losses of transmission line.
When 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.
When 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.
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.