 Good evening one and all. Our today's topic is circulator. We'll see the details of the circulators. Myself, Piyusha Shatgar. These are the learning outcomes. At the end of this session, students will be able to differentiate between circulator and isolator. They will be able to analyze the use of microwave components in the design of microwave system. These are the contents. Circulator is a passive non-reciprocal 3 or 4 port device in which a microwave or radio frequency signal entering any port is transmitted to the next port in rotation only. That is, it will not reverse the direction of the input port. It is a 4 port microwave device which has a peculiar property that each terminal is connected only to the next clockwise terminal. It is a non-reciprocal device with several ports. That means it having the number of n number of ports. So for example, if the input signal is applied to port 1, the signal can just come out of the port 2. The same principle is used when the input signal is applied to port 2. The signal can just output from the port 3. The circulator is also called as a isolator for the outstanding feature that it can transmit high frequency signal energy in one way only. It controls the electromagnetic wave transmission along the circular direction. Generally, we are using the 3 port circulator and 4 port circulator. So these are the types of the circulator, 3 port circulator and 4 port circulator. Now what is 3 port circulator? The circulator which having the 3 ports as shown in this figure port 1, port 2 and port 3. Whereas port 1 is coupled to the next port that is port 2 and port 2 is coupled to the next port that is port 3. If the input is applied to port 1, you are taking the output out of this port 2. Whereas port 1 and port 3 are isolated from each other. So in this case, we are calculating the scattering matrix for this circulator which having the 3 ports and therefore the scattering matrix defined with the order of 3 by 3. So S13, S21 and S32 are the scattering coefficients. Only these parameters are present whereas other parameters are equal to 0. Because if one of the port applied as an input port then the next clockwise port is applied as an output. Whereas the remaining third port is isolated from the first port. And therefore the scattering matrix for this circulator becomes 0 0 1 1 0 0 and 0 1 0. So it is usually called as a y-junction circulator. Looks like a y-letter and therefore it is y-junction circulator. If the input signal is applied to port 1, the signal is coming out of the port 2. Whereas the port 3 is the isolated from the port 1. The insertion loss of the circulator is the loss from port 1 to port 2. While the loss from port 1 to port 3 is referred to as the isolation. It is defined in terms of the decibel value. And the input signal from the port 2, the signal can just output from the port 3. In this case the port 1 is an isolated port. And the input signal from the port 3, the signal can just output from the port 1. Now consider the 4 port circulator which having the 4 ports port 1, 2, 3 and 4. So if the input is applied to port 1, then output is coming out of the port 2. If the input is applied to port 2, then the output is coming out of the port 3. So in that case port 4 and port 1 are isolated from each other. So in this 4 port circulator the scattering matrix defined with these all parameters S21, 12, 13, 14, S23, S24, S31, S32, S34, S41, S42 and S43 remaining diagonal elements are equal to 0. So in this case the scattering matrix defined with this given matrix. 4 port circulator can be made using the 2 magic T also. And a non reciprocal 180 degree phase shifter. When the input is applied to port 1, the output is obtained at the port 2 only. And when the input is applied to port 2, then the output is obtained at port 3 only. Similarly for the port 3 and port 4 as a input. Now consider this is the 4 port circulator, port 1, port 2, port 3 and port 4. So whatever is the input is applied at port 1, it is in mode TE10. This TE10 mode of the signal is transmitted to TE11 mode because of the transmission of the signal from the rectangular to the circular. And therefore whatever is the transmitted signal is in terms of the TE11 mode. This ferrite rod is placed at the center of the circulator. So you have to prove that when the input is applied to port 1, you are getting the output at port 2 only. It will not coming towards this port 3 and port 4. So before going to start the working of this 4 port circulator, you can pause video here and state the properties of ferrites. These are ferrites exhibits strong magnetic ability, ferrites exhibits high resistivity compared with copper in microwave and ferrite exhibits non reciprocal property. So how the working of this 4 port circulator, when the power is applied to port 1 is in TE10 mode and this is converted into TE11 mode because of the signal transmission from rectangular to the circular position. And the power passes port 3 is unaffected since the electric field is not significantly cut at that position. Then the power coming towards this ferrite rod gets rotated with the 45 degree due to this ferrite rod. Then it passes to port 4 again it is unaffected because of the electric field is not significantly cut. And finally it emerges out of the port 2. And when the input is at port 2 having the plane of the polarization already tilted by the 45 degree with respect to the port 1. And this power passes by another 45 degree due to ferrite rod in clockwise direction. This power whose plane of the polarization is now tilted through 90 degree is suitably aligned to port 3. And therefore this signal is emerges out of the port 3. Thus input is applied to port 2. Then you are getting the output out of this port 3. Similarly port 3 is coupled to port 4. And when the input is applied to port 4, it is coming out of the port 1. Thus port 4 is coupled to the port 1. These are the applications of the circulator. So the first application the circulator can be used as a duplexer for a radar antenna system. That is consider this figure with the 4 ports port 1, 2, 3 and 4. Transmitter is connected to the port 1. Whereas the receiver is connected to the port 3. And the radar antenna is connected to the port 2. And the 4 port is terminated. Thus the powerful radar transmitter is isolated from this sensitive receiver. That is port 1. That is the transmitter is connected to the port 2. That is radar antenna. Whereas this port 2 is also connected to the port 3. That is receiver. Thus you can say that the same antenna can be used for both transmission and the reception. And therefore you can say that the circulator can be used as a duplexer. Second application the circulator can be used as a isolator. Isolator is used to pass the signal in one direction only. Thus the one port is terminated from the 3 port circulator to use the 3 port circulator as a isolator. Power loss from port 1 to port 2 is less which is known as the insertion loss. And the power loss from port 2 to port 1 is more which is known as the isolation. Next application is the circulator can be used in the parametric amplifier. So here the 2 3 port circulators are used. The input is applied to the first 3 port circulator to the port 1. And this is the output is going to apply to this tunnel diode. Then this output is coming as the input for the second 3 port circulator. And at the output of the port 2 of second 3 port circulator the amplified signal is obtained according to the property of the parametric amplifier. Thus the circulators can be used for the different applications. These are the references for this session. Thank you.