 Good morning everyone. Myself Piyusha Shedkar. Today we will see the remaining part of the antenna parameters that is part 2. These are the learning outcomes for this session. At the end of this session, students will be able to define the different parameters of antenna. They will be able to explain different properties of antenna. These are the contents for this session. So before going to start the parameters of an antenna, again recall what is an antenna? So antenna is a linking component of guided wave and free space. Source of a radiator of electromagnetic waves. It is a sensor of electromagnetic waves. It is transducer because it converts one type of energy into other form of the energy. It is an impedance matching device. So before going to start the different parameters of an antenna, recall all the parameters we discussed in the last lecture. So the different parameters of an antenna that is radiation pattern, radiation power density, radiation intensity, antenna gain, power gain and the directivity. So these are all the different parameters of an antenna. So these all parameters we have discussed in the last lecture. Now we will see the different again parameters from the seventh. That is antenna impedance to effective area in this lecture. Now consider the next parameter is the antenna impedance. Now what is an antenna impedance? It is denoted with the letter Z. It is defined as the ratio of input voltage to input current. That is Z equal to Vi by Ii. Thus Vi is the input voltage and Ii is the input current. Now consider that the Z is a complex quantity. And therefore it can be written as Z equal to R plus Jx. So here R is the resistive part whereas the X is the reactive part. So R is nothing but it is the addition of the loss resistance and the radiation resistance. That is R equal to RL plus RR. Now suppose the impedance Z is given by Z equal to 50 plus J50 ohm. That is it consists of the resistive as well as the reactive part. Now in this equation if you are considering the imaginary part of the impedance is equal to 0. That is if the impedance is entirely real then the voltage and current are exactly in time phase. Whereas in opposite case if the impedance is entirely imaginary then the voltage leads the current by 90 degrees in phase. Now suppose the impedance having the both resistive as well as the reactive part. Then the impedance has the magnitude which can be calculated by under root reactive part square plus the resistive part square. So for the given value of impedance the magnitude of that impedance becomes equal to 70.71. So for the same impedance you can calculate the phase by taking the ratio of imaginary divided by the real part. And taking the tan inverse of this value we are getting the phase of that antenna. So here for this example we are getting the phase equal to 45 degree. This means that the phase of the current will lag the voltage by 45 degree. Now the next parameter radiation resistance. Now what is the radiation resistance? So radiation resistance is a fictitious resistance that would dissipate an amount of power equal to the radiated power. So mathematically it can be represented by the ratio of power radiated to the I square. And this radiation resistance is nothing but the loss. Now value of the radiation resistance depends on the different parameters. So these parameters are nothing but configuration of antenna. The point where the radiation resistance is considered. The location of an antenna with respect to the ground and other objects. Ratio of length to diameter of the conductor used. Now consider this is the equivalent circuit of an antenna. So here it is the input part, this one is the output part. So if the antenna is considered at the output side that is when the guided wave is radiated into the free space then the antenna is used. Thus you can say that the antenna is an important component between the guided wave and free space. So it is the source, from the source the electromagnetic energy is radiated. It is transmitted through the transmission line as a standing wave. Then this input resistance RR is represents as a radiated energy. Whereas this is the input loss resistance RL. It is represents conduction and dielectric losses of the antenna. Whereas the XA part that is the reactive part input reactance XA represents the energy stored in the field near the antenna. Now consider the next parameter effective length of an antenna. So what is the effective length of an antenna? It gives how far an antenna is effective in transmitting or receiving the electromagnetic wave energy. Now the effective length of an antenna can be defined for transmitting or receiving antenna separately as follows. So first is the effective length of transmitting antenna. It is a length of an equivalent linear antenna that has a constant current along its length and which radiates the same field strength as the actual antenna. And what is the effective length of receiving antenna? It is defined as the ratio of the open circuit voltage developed at the terminals of the antenna under the received field strength. Now the next parameter is the antenna efficiency. So what is the antenna efficiency? It is defined as the ratio of radiated power to the input power. That is if the signal is radiated from the transmitter side and it is passing through the free space the antenna is used. So how much radiated power is received at the receiver side out of the input power is defined with the antenna efficiency. So an antenna is meant nothing but the radiated power given at its input with the minimum losses. So get the maximum efficiency there will be the minimum losses of the signal through the free space. Now the efficiency of an antenna explains how much an amount how much an antenna is able to deliver its output effectively with minimum losses in the transmission line. This is called as the radiation efficiency factor of the antenna which is given by epsilon r that is it gives the radiation efficiency therefore it is written as r. It is the ratio of radiated power to the input power. Now the total efficiency of an antenna is the radiation efficiency multiplied with the impedance matching loss of the antenna when connected to transmission line over the receiver. And the antenna's total efficiency is the antenna's loss due to impedance mismatch and this is nothing but the antenna's radiation efficiency. Thus the equation for the efficiency can be written as the radiated power divided by the total power. It can be also written as the ratio of power gain to the directivity gain. Therefore WR plus WL is considered as the total radiated power where GP is the power gain and the GD is the directive gain. Now loss resistance is due to the ohmic loss in the antenna conductor, dielectric loss, power loss, leakage loss in insulation and loss in earth connection. And in percentage the efficiency can be written as RR upon RR plus RL into 100 where RR is the radiation resistance, RL is the ohmic loss resistance whereas RR plus RL is nothing but the total effective resistance. The total antenna efficiency is always less than the antenna's radiation efficiency. The radiation efficiency is the same as the total antenna efficiency if there is no any losses considered due to the impedance mismatching. Now before going to the next slide you can pause the video here and recall that what are the causes to not get the efficiency equal to 100%. So antenna efficiency you are not getting the maximum because of the losses. And these losses are due to the conduction losses due to finite conductivity of metal that forms the antenna. Dielectric losses due to conductivity of a dielectric material near an antenna and due to the mismatching of the impedance. Now the next parameter is the effective area. So what is effective area? It is nothing but the area over which the antenna extracts electromagnetic energy from the traveling electromagnetic waves. It can also be defined as the ratio of power received at the antenna load terminal to the power density of incident wave. It is denoted with the AE letter. It is nothing but lambda square by 4 pi gd where A is nothing but it is the ratio power received to the pointing vector. It is given by the directive gate. Hence the effective area simply represents how much power is captured from the plane wave and delivered by the antenna. By the reciprocity theorem you know that the total characteristics of the reciprocity theorem for transmitting and the receiving antenna should be same. The direction in which antenna radiates maximally and the direction from which the antenna receives maximum power should be same. The antenna does not receive any power from the radiation arriving from the direction of the null. Next property is an antenna maximally responds to that polarization which it generates while transmitting. While effective aperture of an antenna is a parameter defined for the receiving antenna. It tells the capability of an antenna to tap power from the radiation arriving from certain direction. These are the references for this session. Thank you.