 भुड़ाप्तानु नेव्रिवन, तुड़े भी विल सी तोपिक आंटिना बेसिक्स, मैसर्फ प्युशा शेटगर. तीस आर दे लेरनिग अुटकम्स फर दी सेशन, at the end of this session, students will be able to analyze the electric and magnetic field emission from various basic antenas and they will be able to explain basic principle of radiation and list different applications of antenas. these are the contents for this session. now, see the antenna basics. antenas are nothing but the connecting link between the transmitter, free space and receiver. and it is also considered as the basic component of an electric system. it is an electric device which converts electric power into radio waves or radiowaves into electric power. thus, antenna can be used to convert one form of energy into other form. In the world, antennas are like our electronic eyes and ears. They are our links with the space. Antennas used with radio transmitter or radio receiver. Antennas plays an important role in our civilization. Now before going to start the antennas in details, you can pause the video here for 2 seconds and recall that what is meant by electromagnetic waves. Antennas are related to the EM waves. Therefore recall here what is electromagnetic waves. Yes, the electromagnetic waves are nothing but it is the combination of electric field and the magnetic field. These 2 fields are perpendicular to each other. And the electric field and the magnetic fields are perpendicular to each other and also they are travelling into the particular direction, x-direction, y-direction or z-direction. So these types of waves include radio waves, microwaves, infrared, etc. Light, ultraviolet, x-rays and gamma rays. Now the electromagnetic waves. In EM waves the electric field and the magnetic fields are perpendicular to each other. Thus in this figure the red wave shows the magnetic field and the blue wave shows by the electric field. As you know that the electric field and the magnetic fields are perpendicular to each other and the wave is travelled in the direction of the propagation of the wave. Here in this example the wave is travelling in x-direction. Again you can see that the electromagnetic waves which having the electric field intensity and the magnetic field intensity these 2 fields are varying fields and the wave is also perpendicular to the direction of the propagation of the wave and the distance between the 2 successive crests or trough is known as the wavelength. Now the electromagnetic waves can be defined into waves, guided waves and unguided waves. The guided waves defined by cables, waveguides and cosy optical system. These type of transmission line used at the different frequencies such as cables are used at frequencies below 35 GHz waveguides used between 0.4 GHz to 350 GHz whereas cosy optical system used above 30 GHz. Now what is the meaning of these guided electromagnetic waves? As you know that the transverse electromagnetic waves cannot support to the waveguide that is TM waves travel in cables and the cosy optical system which is same as nothing but free space while TM and TE waves or the combination of both these waves can be travelled through the waveguide. Here in waveguide the electric or magnetic field components are in the direction of the propagation of the wave. EM wave becomes it bounces back and forth on the inner walls of the waveguide which having the different frequency limits you can define these different frequency limits with the lower and the upper frequency limit whereas the cross section dimension of this type of wave proportional to the wavelength. Now this is a diagram shows the guided wave to free space transition. Here the transmitting antenna is connected to the generator side or it is also known as the transmitter side. From this the electromagnetic wave is generated which is travelling through this transmission line such as the waveguide and again a transition it takes the transition in tapered form and it goes to the free space that is in antenna. Thus the antenna provides the vital element it plays an important role in wireless technology and therefore the vital element of the wireless technology is nothing but the antenna. Now the basic elements of the antenna now consider the current carrying conductor is placed and the electrons are flowing through this conductor when this movement of the electrons is occur it creates the two fields these fields dealing with the time and space quadrature from the antenna this field produces a radiating wave pattern we can represent this radiations by the vectors and the wave associated with this vector is travelling wave pattern. So here you can observe that this wave having the electric field as well as the magnetic field and these two fields are varying with time phase and the space quadrature and the polarity of the antenna determined by plane of the electric field here the electric field and magnetic field perpendicular to each other and also perpendicular to the direction of the propagation of the wave again you can see that these are the field variation with the current direction as you know that the field variation is occur when the current carrying conductor is placed and the electrons are flowing through this conductor when the flux linked to this conductor changes the current start to flow through this conductor so here the direction of the electric field is from positive to negative and thus the current direction is in upward direction so here the field variation is considered with the direction of the current now the antenna can be used either as a transmitting antenna and therefore the antenna is also called as the duplexer in two way communication the same antenna can be used as a transmitter or the receiver now what is the transmitting antenna at the transmitting antenna the generator is connected it converts electrical signal into the electromagnetic waves and it radiates them into the free space and now this transmission line is connected to the source or generator this line energy is guided as plane transfers electromagnetic wave with a very little loss is considered and the spacing between the line is having a very small fraction of the wavelength which is denoted with the letter lambda as this line is opened out in free space it acts like an antenna this wave sees the currents on the transmission line is flow out but the fields associated with them is keep going on antennas appear to the transmission line as a resistance and therefore it is called as radiation resistance denoted with the rr now the receiving antenna at the receiver side the electromagnetic waves converts into the electrical signal in the reception side an antenna intercepts some of the power of the radio waves in order to produce an electric current at its terminal whereas this signal is amplified at the receiver side antennas are essential components of all radio equipment so here it is the example of the figure with the transmitter antenna and the receiver antenna so in transmitter the generator can be connected to this transmitting antenna here the electromagnetic signals are generated which are travelling through the transmission line we can consider it as a waveguide it opened out and it acts as an antenna again from this free space this signal is coming towards the receiver side and at the receiver side this signal is amplified so we termed as a aerial the plural of it is known as the antennae or antennas nowadays antennas have undergone many changes in accordance with their size and shape so there are the many types of the antennas can be used depend on the number of applications so what are the applications of the antennas? antennas are essential components of all equipment that uses radio they are used in systems such as radio broadcasting broadcast television two way radio communication receivers etc radar cell phones and satellite communication other devices such as garage door opener wireless microphones wireless computer networks and RFID tags etc now what is the principle of the antenna? under time varying condition the Maxwell equations indicate the radiation of electromagnetic energy from current source that is it is related to the accelerated charge this happens at all frequencies but is significant as long as the size of the source region is not comparable to the wavelength while the transmission lines are designed to minimize this radiation loss radiation into the free space becomes the main purpose in case of the antenna the basic principle of the antenna is produced by the accelerated charge for that consider this is the equation the basic equation for the principle of the radiation is i dot l equal to q v dot whereas i dot is the time changing current in ampere per second and the v dot is the time changing velocity thus the time changing current radiates and the accelerated charge also radiates for the steady state harmonic variation usually we focus on time changing current and for transient we focus on the accelerated charge whereas this radiated power is proportional to the square of the i dot l or q v dot now this is the figure shows the principle of the antenna as this is considered as with respect to the time changing current and the accelerated charge now while designing the antenna the following factors are to be considered the strength of the radiated field in different directions the total power radiated is compared with the driving power of the antenna consider the impedance of the antenna and the frequency range for that particular antenna now these are the types of the antennas mainly the three types of the antennas isotropic antenna, directional antenna and the omni-directional antenna so what is isotropic antenna in this type of the antenna the signal radiates uniformly in all directions and generally it is also used as a reference antenna in directional antenna the signal radiates maximum signal in only one direction as a major loop and the minimum in other direction as a minor loop whereas in omni-directional antenna it radiates signal in only one direction may be the x-axis, y-axis or the z-axis and the no-back loop is present in case of the omni-directional antenna so these are the basic types of the antennas that is the antennas can be divided into various types depending on the physical structure of the antenna the frequency range of the antenna and the mode of application of the antenna so the physical structure is considered for the following types of the antennas wire antennas, aperture antennas, reflector antennas lanes, micro strip and the air antennas whereas the frequency can be defined with the different ranges of the frequencies such as the very low frequency, low frequency medium frequency, high frequency very high frequency, ultra high frequency super high frequency, micro wave, radio waves etc and the mode of the operation the types of antennas according to the mode of the applications point to point communication, broadcasting applications radar communication, satellite communication etc. now in the antenna theory which follows the reciprocity theorem during transmission or reception an antenna exhibits, it should be exhibit it should having the identical impedance same directional pattern, same effective height thus the transmission and the reception antenna can be used interchangeably because it having all these characteristics are same, the medium must be linear, passive and the isotropy now this is although the antenna can be used as about transmitting antenna and the receiving antenna the properties of the antenna being unchangeable it is known as the reciprocity theorem these properties are nothing but the equality in directional patterns, equality in directivities effective lanes and the equality in the antenna impedances these are the references for this session thank you