 Good afternoon everyone, myself Piyusha Shedgarh. In this session we will see the rectangular waveguide fundamentals. These are the possible outcomes for this session. Learning outcomes at the end of this session, students will be able to distinguish between the transmission line and waveguide, they will be able to explain the waveguide structure propagating in T, Tm and transverse electromagnetic mode. These are the contents for this session. Before going to start the topic, we will pause the video here for a second and recall that what is the range of frequency used for microwave signal. For that you can refer frequency spectrum. Yes, as you know that the microwave signal which having the highest frequency range, therefore the microwave spectrum generally having the range of frequency is in gigahertz and generally 1 gigahertz to 100 gigahertz is used for the microwave signals. At the highest frequency it is not possible to transmit the signal through the transmission line and the cables because the losses will be occur while transmitting these signals. So higher than the 3 gigahertz frequency it is not possible to transmit the signal. So to transmit the electromagnetic signal a metallic tube can be used. What is waveguide? A hollow metallic tube of uniform cross section for transmitting electromagnetic waves by successive reflections from the inner walls of the tube is called waveguide. Now let us see the comparison between the waveguide and two wire transmission line. In two wire transmission line two or more conductors are separated by some insulating medium. While in waveguide type of a waveguide metal waveguide are enclosed conductor filled with an insulating medium while a dielectric waveguide consist of multiple dielectrics. In transmission line normal operating mode is transverse electromagnetic mode while in case of waveguide transfer of electric or transfer magnetic mode is used. In transmission line no cutoff frequency is considered that is the highest frequency also pass through the transmission line but there is a cutoff frequency is considered for the respective transverse electric or transverse magnetic mode in case of the waveguide. System of propagation is in accordance with the field theory in transmission line while in case of waveguide the system of propagation is in accordance with the circuit theory. A two conductor structure is used in transmission line while one conductor structure is used in waveguide. At high frequencies significant signal attenuation is occur due to the conductor and dielectric losses in transmission line. At high frequencies the signal attenuation is lower as compared to the transmission line in case of waveguide. Small cross section transmission line that is coaxial cables can only transmit the low power while in waveguide metal waveguide can transmit high power levels also. Now these are the different types of the transmission lines. So coaxial line to wire lines and the microstrip lines are not used for the highest frequency signal. These highest frequency signal can pass through the waveguides. So mostly the common waveguides used are rectangular waveguide and circular waveguide. As shown in figure the rectangular waveguide is rectangular in structure while the circular waveguide is circular in structure. So rectangular waveguide having the dimensions breadth and width while in circular waveguide radii are considered. So some waveguide fundamentals, waveguide consists of a metallic conductor with or without dielectric coating. In order to keep the conductivity of the interior surface of waveguide as high as possible these surfaces are coated with copper, silver or gold. Dimension of the waveguide determines the operating frequency range, mode of operation and power capacity of rectangular waveguide. So consider this is the rectangular waveguide with the dimensions a and b. Dimensions a which is the longest side which determines the frequency range and mode of propagation while the dimension b is usually half of the dimension a which determines the attenuation and power capacity of the signal. So this is the electromagnetic wave as you observe from this wave the electric field and the magnetic fields are perpendicular to each other which is supposed to be transmit through the rectangular waveguide. So when it transmit through the rectangular waveguide varying electric field is generated and this varying electric field can generate the varying magnetic field thus the electromagnetic wave is generated. Thus there is no any source is required to generate the electromagnetic wave and we can say that electromagnetic wave is a self-generated wave. At the lowest frequency of operation dimension of the longest side of the waveguide is usually made equal to one half of the wavelength. This frequency is known as the waveguide cutoff frequency and at this cutoff frequency and below this cutoff frequency the signal cannot be transmitted through the rectangular waveguide. Above this cutoff frequency only the energy is transmitted through the rectangular waveguide. So how the wave is propagated through the rectangular waveguide? Consider this is the figure here the angles are given angle of incidence and the angle of reflection can be decided according to the frequency. So first figure at high frequency the angle of incidence is greater than angle of incidence and the angle of reflection is greater thus the path between the signal throughout the wall of the rectangular waveguide is also high. Consider the medium frequency at medium frequency and lower cutoff lower frequency the angle of incidence equal to angle of reflection decreases and thus the path of the electromagnetic signal is also decreases. But at cutoff frequency when the signal try to transmit through the rectangular waveguide the signal bounces back and forth only and thus it has no any path to transmit through the rectangular waveguide. So at cutoff frequency and at the lower cutoff frequency the signal cannot transmit through the rectangular waveguide. From the size of the waveguide operating frequency range can be decided. The size of the waveguide chosen such that its rectangular width is greater than one half the wavelength but less than the one wavelength at the operating frequency. Now consider again this figure in which the rectangular waveguide is considered for the rectangular coordinate system. So breadth is placed along the x axis with the a and the width that is b is placed along the y axis. Waveguide is filled with an air as a dielectric medium and the propagation of the wave is along the z axis. The electromagnetic wave inside a waveguide can have an infinite number of patterns which are called as a modes. In an electromagnetic wave electric field and the magnetic fields are always perpendicular to each other. Now these are the different modes of the propagation of the wave. Consider the first mode transverse electric mode. It is also called as a H wave. In this mode electric field is always transverse to the propagation. That is no electric line is in the direction of the propagation. If the direction of the propagation is in z direction thus the z component of electric field is equal to 0 while the magnetic field component is present. Now consider the next mode transverse magnetic mode. It is also known as a E wave. In this mode the magnetic field is always transverse to the propagation. That is no magnetic line is in the direction of the propagation. Thus the z component of magnetic field is equal to 0 while the electric field component of z is not equal to 0. Transverse electric and magnetic mode. This mode having E z as well as H z is equal to 0. That is both components are not present in case of the transverse electromagnetic mode. Rectangular wave guide cannot support this type of the wave. Hybrid wave. In this mode neither electric nor magnetic fields are purely transverse to the direction of the propagation. Therefore this mode having both the components electric component as well as the magnetic components. So these are the different T and T M modes are shown in this figure. So in this figure the blue line first electric field is perpendicular to the direction of the propagation of the wave while in case of a T M mode the magnetic field is perpendicular to the direction of the propagation of the wave. Whereas from this figure you can say that magnetic flux lines appears as a continuous loop while electric flux lines appear with the beginning and the end points. For the T M mode E z component equal to 0 and for T M mode H z component is equal to 0. These are the references for this session. Thank you.