microwave-engineering

microwave-engineering

1. EC402 Microwave Engineering

2. 2 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Electromagnetic Spectrum

3. 3 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Electromagnetic Spectrum

4. 4 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Electromagnetic Spectrum Microwave frequency range 1-30GHz wave length 30cm-1cm

5. 5 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Microwave Frequency Range

6. 6 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Electromagnetic Spectrum

7. 7 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Electromagnetic Spectrum

8. 8 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Electromagnetic Spectrum

9. Small size wavelength f=1GHz λ =c/f=3x10 10 /1x10 9 =30cm f=30GHz λ =c/f=3x10 10 /30x10 9 =1cm Wave lengths are same as dimensions of components, so distributed circuit elements or transmission theory is applied. 9 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Characteristics of Microwaves

10. 10 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Characteristics-Large Bandwidth Large Bandwidth High transmission rates used for communication World’s data, TV and telephone communications are transmitted long distances by microwaves between ground stations and  communications satellite

11. 11 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Characteristics-Line of sight propagation

12. 12 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Characteristics-Line of sight propagation

13. 13 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Characteristics-Line of sight propagation

14. 14 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Characteristics-Transmission Through Ionosphere

15. 15 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Characteristics-Transmission Through Ionosphere

16. 16 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Characteristics-Transmission Through Ionosphere

17. 17 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Characteristics- Reflection From Metallic Surfaces

18. 18 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Characteristics

19. 19 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Characteristics- Heating

20. 20 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Characteristics- Heating

21. 21 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Characteristics- Heating

22. 22 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Characteristics- Microwave Resonance Microwave Resonance: Molecular, atomic and nuclear systems exhibit resonance when Present electromagnetic Fields Several resonance absorption lines are in microwave range

23. 23 9/2/2015 Microwave Engineering Application- Communications National Institute of Technology, Warangal Point to point communications GSM 1.8 and 1.9 GHz DVB-SH, 1.452, 1.492 GHz

24. 24 9/2/2015 Microwave Engineering Wi-Fi Wireless LAN networks 2.4GHz ISM band National Institute of Technology, Warangal

25. 25 9/2/2015 Microwave Engineering Wimax Wimax (Worldwide Interoperability for Microwave Access) 2 to 11 GHz PMP-Point to multipoint links National Institute of Technology, Warangal

26. 26 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Wimax , WiFi

27. 27 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Satellite Communications L band (1-2 GHz )Global Positioning System (GPS) carriers and also satellite mobile phones, such as Iridium; Inmarsat providing communications at sea, land and air; WorldSpace satellite radio.

28. 28 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Satellite Communications

29. 29 9/2/2015 Microwave Engineering RADAR National Institute of Technology, Warangal

30. 30 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering RADAR Radar  is an object-detection system that uses  radio waves  to determine the range, altitude, direction, or speed of objects. It can be used to detect  aircraft , ships,  spacecraft ,  guided missiles ,   motor vehicles ,  weather formations , and terrain. Aviation Marine Meteorologists

31. 31 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Heating Domestic Application: Heating, Microwave oven Industrial Application: Food, Rubber, leather, chemical and textile , pharmaceutical industries

32. 32 9/2/2015 Microwave Engineering Remote Sensing Remote sensing: Remote sensing  is the acquisition of information about an object or phenomenon without making physical contact with the object and thus in contrast to on site observation. National Institute of Technology, Warangal

33. 33 9/2/2015 Microwave Engineering Remote Sensing National Institute of Technology, Warangal

34. 34 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Radio Astronomy Radio Astronomy: Radio astronomy  is a subfield of  astronomy  that studies celestial objects at  radio  frequencies. 

35. 35 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Radio Astronomy Arecibo 305 m (  about 20 acres) radio telescope, located in a natural valley in Puerto Rico.

36. 36 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Radio Interferometery The  Very Large Array , an  interferometric array  formed from many smaller telescopes

37. 37 9/2/2015 Microwave Engineering Medical Application National Institute of Technology, Warangal

38. 38 9/2/2015 Microwave Engineering Microwave Imaging Microwave imaging  is a science which has been evolved from older detecting/locating techniques (e.g.,  radar ) in order to evaluate hidden or embedded objects in a structure (or media)using electromagnetic (EM) waves in  microwave  regime (i.e., ~300 MHz-300 GHz) National Institute of Technology, Warangal

39. 39 9/2/2015 Microwave Engineering Microwave Imaging concealed weapon detection at security check points, structural health monitoring through-the-wall imaging. Disbond detection in strengthened concrete bridge Corrosion and precursor pitting detection in painted aluminum and steel substrates Flaw detection in spray-on foam insulation National Institute of Technology, Warangal

40. 40 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Industry Applications Microwave oven Drying machines – textile, food and paper industry for drying clothes, potato chips, printed matters etc. Food process industry – Precooling / cooking, pasteurization / sterility, hat frozen / refrigerated precooled meats, roasting of food grains / beans. Rubber industry / plastics / chemical / forest product industries Mining / public works, breaking rocks, tunnel boring, drying / breaking up concrete, breaking up coal seams, curing of cement. Drying inks / drying textiles, drying / sterilizing grains, drying / sterilizing pharmaceuticals, leather, tobacco, power transmission. Biomedical Applications ( diagnostic / therapeutic ) – diathermy for localized superficial heating, deep electromagnetic heating for treatment of cancer, hyperthermia ( local, regional or whole body for cancer therapy).

41. 41 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Advantages Large Bandwidth : It is very good advantage, because of this, Microwaves are used for Point to Point Communications.

42. 42 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Advantages Better Directivity

43. 43 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Advantages Better Directivity : At Microwave Frequencies, there are better directive properties. This is due to the relation that as Frequency Increases, Wavelength decreases and as Wavelength decreases Directivity Increases and Beam width decreases. So it is easier to design and fabricate high gain antenna in Microwaves.

44. 44 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Advantages Small Size Antenna

45. 45 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Advantages Low Power Consumption

46. 46 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Advantages Low Power  Consumption :The power required to transmit a high frequency signal is lesser than the power required in transmission of low frequency signals. As Microwaves have high frequency thus requires very less  power.

47. 47 9/2/2015 Microwave Engineering Advantages National Institute of Technology, Warangal Effect Of Fading Space wave Sky wave

48. 48 9/2/2015 Microwave Engineering Advantages National Institute of Technology, Warangal Effect Of Fading:  The effect of fading is minimized by using Line Of Sight propagation technique at Microwave Frequencies. While at low frequency signals, the layers around the earth causes fading of the signal. Space wave Sky wave

49. 49 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Fresnel Zone

50. 50 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Fresnel Zone there should be no reflective objects in the 1st Fresnel zone even  Fresnel zone are  out of phase  with the direct-path wave and reduce the power of the received signal odd  Fresnel zone are  in phase  with the direct-path wave and can enhance the power

51. 51 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Limitations of Tubes at High Frequencies

52. 52 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Vacuum tubes- Triode

53. 53 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Triode Amplifier Circuit

54. 54 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Limitations at Higher Frequencies Inter electrode Capacitance

55. 55 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Inter electrode Capacitance Limitations at Higher Frequencies At frequencies greater than 1 GHz Limitations at Higher Frequencies

56. 56 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Leads: Leads are used for physical support, to transfer power and sometimes as a  Heatsink .  Limitations at Higher Frequencies Limitations at Higher Frequencies

57. 57 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Leads: Leads are used for physical support, to transfer power and sometimes as a  Heatsink .  Limitations at Higher Frequencies In fact, any wires or component leads that have current flowing through them create magnetic fields. When these magnetic fields are created, they can produce an inductive effect. Thus, wires or components leads can act as inductors if they are long enough Limitations at Higher Frequencies

58. 58 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Parasitic Inductance and capacitance becomes very large At Microwave frequencies Limitations at Higher Frequencies Limitations at Higher Frequencies

59. 59 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Limitations at Higher Frequencies Reduce length of and area of leads, in turn reduces Power handled. Limitations at Higher Frequencies

60. 60 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Limitations at Higher Frequencies Input conductance loads the circuitry, efficiency reduces. Limitations at Higher Frequencies

61. 61 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Lead Inductance

62. 62 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Inter electrode Capacitance

63. 63 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Input Impedance Input Voltage

64. 64 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Input Impedance Input Current

65. 65 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Input Impedance Input Admittance

66. 66 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Input Impedance

67. 67 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Input Impedance Input Impedance

68. 68 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Input Impedance Input Impedance Input conductance loads the circuitry, efficiency reduces.

69. 69 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Gain Bandwidth

70. 70 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Gain Bandwidth

71. 71 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Gain Bandwidth

72. 72 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Gain Bandwidth

73. 73 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Gain Bandwidth

74. 74 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Gain Bandwidth

75. 75 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Gain Bandwidth

76. 76 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Gain Bandwidth

77. 77 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Gain Bandwidth Gain bandwidth product is independent of frequency, hence is constant. Hence resonant circuits are reentrant or slow wave structures

78. 78 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Transit Time

79. 79 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Transit Time

80. 80 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Transit Time

81. 81 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Transit Time

82. 82 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Transit Time

83. 83 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Transit Time In the positive half-cycle, grid potential attracts the electron beam and supplies energy to it

84. 84 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Transit Time In the negative half-cycle, it repels the electron beam and extracts energy from it.

85. 85 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Transit Time As a result, the electron beam oscillates back and forth in the region between the cathode and the grid, and may even return to the cathode. The overall result is a reduction of the operating frequency of the vacuum tube.

86. 86 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Transit Time Reduce Transit Time Increasing the anode voltage Decreasing the inter-electrode spacing However, the increase in anode voltage will increase the power dissipation, whereas the decrease in inter-electrode spacing will increase the inter-electrode capacitance.

87. 87 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Transit Time The increase in inter-electrode capacitance can be reduced by reducing the area of the electrodes, but this will reduce anode dissipation and hence the output power.

88. 88 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering RF Loss- Skin Effect Loss

89. 89 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering RF Loss- Skin Effect Loss

90. 90 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering RF Loss- Skin Effect Loss Skin effect loss At a high frequency, current has a tendency to concentrate around the surface rather than being distributed throughout the cross section. This is known as skin effect. It reduces the effective surface area, which in turn increases the resistance and hence the loss of the device. Resistance loss is also proportional to the square of the frequency. Losses due to skin effect can be reduced by increasing the current-carrying area, which, in turn, increases the inter-electrode capacitance and thus limits high frequency operations.

91. 91 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering RF Loss- Dielectric Loss

92. 92 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering RF Loss- Dielectric Loss Dielectric loss Dielectric loss in a material is proportional to frequency, and hence plays an important role in the operations of high-frequency tubes. This loss can be avoided by eliminating the tube base and reducing the surface area of the dielectric materials, and can be reduced by placing insulating materials at the point of minimum electric field.

93. 93 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Radiation Loss

94. 94 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Radiation Loss Radiation loss At higher frequencies, the length of the leads approaches the operating wavelength, and as a result these start radiating. Radiation loss increases with the increase in frequency and hence is very severe at microwave frequencies. Proper shielding is required to avoid this loss. Radiation loss can be minimized by enclosing the tubes or using a concentric line construction

95. 95 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Resonator A  resonator  is a device or system that exhibits  resonance  or resonant behavior , that is, it naturally  oscillates  at some  frequencies , called its resonant frequencies , with greater  amplitude  than at others.

96. 96 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Resonant Circuit

97. 97 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Resonant Circuit An electrical circuit composed of discrete components can act as a resonator when both an  inductor  and  capacitor  are included. Such  resonant circuits  are also called  RLC circuits  after the circuit symbols for the components.

98. 98 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Cavity Resonator

99. 99 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Cavity Resonator A  cavity resonator , usually used in reference to electromagnetic resonators, is one in which waves exist in a hollow space inside the device

100. 100 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Cavity Resonator Due to the low resistance of their conductive walls, cavity resonators have very high  Q factors ; that is their  bandwidth , the range of frequencies around the resonant frequency at which they will resonate, is very narrow. Thus they can act as narrow bandpass filters . Cavity resonators are widely used as the frequency determining element in  microwave oscillators . Their resonant frequency can be tuned by moving one of the walls of the cavity in or out, changing its size.

101. 101 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Rectangular Cavity Resonator

102. 102 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Rectangular Cavity Resonator For a > b < d, the dominant mode is the TE101 mode.

103. 103 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Rectangular Cavity Resonator The electric field lines start from top and bottom, positive and negative charges are induced, hence forms capacitor The current flows via side walls and hence serve as inductor, hence the enclosed volume behaves as tank circuit.

104. 104 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Circular Cavity Resonator

105. 105 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Circular Cavity Resonator TE111 mode is the dominant mode.

106. 106 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Quality Factor The  Q factor  (quality factor) of a resonator is a measure of the strength of the damping of its oscillations, or for the relative linewidth . the  Q  factor is 2 π  times the ratio of the stored energy to the energy dissipated per oscillation cycle the  Q  factor is the ratio of the resonance frequency  ν  and the full width at half-maximum (FWHM) bandwidth   δν  of the resonance:

107. 107 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Quality Factor

108. 108 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Reentrant Cavity Resonator

109. 109 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Reentrant Cavity Resonator

110. 110 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Reentrant Cavity Resonator

111. 111 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Reentrant Cavity Resonator

112. 112 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Excitation Wave Modes Loop coupling Probe coupling

113. 113 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Excitation Wave Modes Probe coupling

114. 114 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Excitation Wave Modes Loop coupling

115. 115 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Aperture Coupling Aperture coupling

116. 116 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Coupling Between Waveguides Directional Coupler

117. 117 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Linear Beam Tubes- Otype Tubes Electric Field is applied to the accelerate or decelerate the Electron beam Magnetic Field is applied along the axis to Focus the electron beam.

118. 118 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron an electron tube that generates or amplifies microwaves by velocity modulation.

119. 119 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron an electron tube that generates or amplifies microwaves by velocity modulation.

120. 120 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Velocity Modulation Velocity of electrons accelerated by high DC Voltage

121. 121 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Velocity Modulation Gap Voltage applied at Buncher grids Where

122. 122 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Velocity Modulation Gap Voltage applied at Buncher grids Where

123. 123 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Velocity Modulation Average transit time through buncher gap

124. 124 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Velocity Modulation

125. 125 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Velocity Modulation Average Voltage across the buncher gap

126. 126 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Velocity Modulation

127. 127 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Velocity Modulation

128. 128 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Velocity Modulation

129. 129 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Velocity Modulation

130. 130 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Velocity Modulation Equation for Velocity Modulation

131. 131 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Bunching Process

132. 132 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Bunching Process

133. 133 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Bunching Process

134. 134 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Bunching Process

135. 135 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Bunching Process Distance travelled by the electrons in drift space.

136. 136 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Current Modulation Beam Current varies with the applied RF voltage –current modulation. Fundamental component of current Current becomes maximum at

137. 137 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron- Current Modulation Optimum distance for bunching

138. 138 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron

139. 139 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Applegate Diagram

140. 140 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Output Power

141. 141 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Output Power

142. 142 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Efficiency Theoretical efficiency is 58% Where as practical efficiency is 15% to 30%

143. 143 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Voltage Gain

144. 144 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Typical Values

145. 145 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Applications As power output tubes in UHF TV transmitters in troposphere scatter transmitters satellite communication ground station radar transmitters

146. 146 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron

147. 147 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Multi cavity Klystron

148. 148 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Reflex Klystron

149. 149 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Reflex Klystron

150. 150 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Velocity Modulation Velocity of the electrons in entering the cavity gap

151. 151 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Velocity Modulation Exit Velocity of the electrons in leaving the cavity gap

152. 152 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Velocity Modulation Retarding Electric Field

153. 153 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Velocity Modulation Force equation of one electron assuming V 1 <<( V r +V o )

154. 154 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Reflex Klystron Integrating

155. 155 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Reflex Klystron Integrating

156. 156 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Reflex Klystron Integrating

157. 157 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Reflex Klystron Integrating

158. 158 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Reflex Klystron

159. 159 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Reflex Klystron

160. 160 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Reflex Klystron

161. 161 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Transit Time Round trip transit time in the repeller region

162. 162 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Transit Time

163. 163 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Applegate Diagram

164. 164 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Applegate Diagram

165. 165 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Efficiency

166. 166 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Efficiency of Reflex Klystron

167. 167 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Characteristics of Reflex Klystron

168. 168 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Electronic Admittance

169. 169 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Electronic Admittance

170. 170 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Electronic Admittance Bunched electrons return to the cavity gap a little before the transit time, current leads the behind the field- capacitance appears in the circuit

171. 171 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Electronic Admittance Bunched electrons return to the cavity gap a little after to The ac current lags the field –inductance reactance appears in the circuit

172. 172 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Electronic Admittance Condition for oscillation Ge is negative and total conductance in the circuit is negative – Ge > Gc+Gl

173. 173 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Applications Low power oscillator- 10mw to 500mw Frequency 1-25GHz Local Oscillator in commercial , Military, Air borne Doppler radar and missiles.

174. 174 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Tuning Klystron Electronic Tuning

175. 175 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Tuning Klystron Mechanical Tuning: By changing capacitance or inductance

176. 176 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron

177. 177 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Klystron Output is via a co-axial pin, and the device can be mechanically tuned with the screw on the left, which applies vertical compression to the metal envelope.

178. 178 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Amplitude Modulation -Klystron

179. 179 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Frequency Modulation Klystron

180. 180 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Slow Wave Structures Non Resonant periodic circuits Produce large gain over wide bandwidth

181. 181 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Slow Wave Structures

182. 182 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Slow Wave Structure

183. 183 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Phase Velocity

184. 184 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Group Velocity

185. 185 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Travelling wave tube

186. 186 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Travelling wave tube

187. 187 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Travelling wave tube Amplifiers in  satellite   transponders , where the input signal is very weak and the output needs to be high power. TWTA transmitters are used extensively in  radar , particularly in airborne  fire-control radar  systems, and in  electronic warfare  and self-protection systems

188. 188 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Linear Beam tubes –O type Klystron – Resonant , standing wave Reflex Klystron- Resonant, standing wave Travelling wave tube- Non resonant, travelling wave

189. 189 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Travelling wave tube Amplifies a wide range of  frequencies , a wide  bandwidth and low noise. Bandwidth two  octaves , while the cavity versions have bandwidths of 10–20%.  Operating frequencies range from 300 MHz to 50 GHz. The power gain of the tube is on the order of 40 to 70  decibels Output power ranges from a few watts to  megawatts

190. 190 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Octave  A frequency is said to be an  octave  in width when the upper  band frequency  is twice the lower band frequency

191. 191 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Crossed Field tubes –M type Crossed-field tubes derive their name from the fact that the dc electric field and the dC magnetic field are perpendicular to each other. They are also called M –type tubes

192. 192 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Cylindrical Magnetron

193. 193 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Travelling wave Magnetron Depend upon the interaction of electrons with a rotating electromagnetic field of same angular velocity. Provide oscillations of very high peak power and hence are useful in radar applications

194. 194 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Cavity Magnetron Fig ( i ) Major elements in the Magnetron oscillator

195. 195 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Anode Assembly

196. 196 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Construction Each cavity in the anode acts as an inductor having only one turn and the slot connecting the cavity and the interaction space acts as a capacitor. These two form a parallel resonant circuit and its resonant frequency depends on the value of L of the cavity and the C of the slot. The frequency of the microwaves generated by the magnetron oscillator depends on the frequency of the RF oscillations existing in the resonant cavities.

197. 197 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Crossed Field tubes –M type

198. 198 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Reentrant Cavity

199. 199 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Reentrant Cavity E B

200. 200 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Crossed Field tubes –M type

201. 201 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Description Magnetron is a cross field device as the electric field between the anode and the cathode is radial whereas the magnetic field produced by a permanent magnet is axial. A high DC potential can be applied between the cathode and anode which produces the radial electric field. Depending on the relative strengths of the electric and magnetic fields, the electrons emitted from the cathode and moving towards the anode will traverse through the interaction space as shown in Fig. (iii). In the absence of magnetic field ( B = 0), the electron travel straight from the cathode to the anode due to the radial electric field force acting on it, Fig (iii) a.

202. 202 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Cavity Magnetron

203. 203 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Cavity Magnetron

204. 204 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Cavity Magnetron

205. 205 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Cavity Magnetron

206. 206 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Crossed Field tubes –M type

207. 207 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Description If the magnetic field strength is increased slightly, the lateral force bending the path of the electron as given by the path ‘ b ’ in Fig. (iii). The radius of the path is given by, If the strength of the magnetic field is made sufficiently high then the electrons can be prevented from reaching the anode as indicated path ‘ c ’ in Fig. (iii)), The magnetic field required to return electrons back to the cathode just grazing the surface of the anode is called the critical magnetic field ( B c ) or the cut off magnetic field. If the magnetic field is larger than the critical field ( B > B c ), the electron experiences a greater rotational force and may return back to the cathode quite faster.

208. 208 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Crossed Field tubes –M type Fig (iii) Electron trajectories in the presence of crossed electric and magnetic fields (a) no magnetic field (b) small magnetic field (c) Magnetic field = Bc (d) Excessive magnetic field

209. Effect of electric field Effect of magnetic field Effect of Crossed -Fields

210. 210 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Hull Cut off Condition

211. 211 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Crossed Field tubes –M type Force due to magnetic field on charge Q moving with velocity v Force on electron moving with velocity v

212. 212 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Crossed Field tubes –M type

213. 213 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Crossed Field tubes –M type Force due to electric field on electron

214. 214 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Crossed Field tubes –M type Magnetic Field Bz az

215. 215 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Equations of electrons in motion Acceleration due to electric field

216. 216 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Equations of Electrons in motion

217. 217 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Hull Cut off Condition Rearranging the equation (2)

218. 218 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Hull Cut off Condition

219. 219 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Angular Velocity

220. 220 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Kinetic Energy of Electrons Velocity of electrons

221. 221 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Crossed Field tubes –M type

222. 222 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Crossed Field tubes –M type

223. 223 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Crossed Field tubes –M type

224. 224 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Crossed Field tubes –M type

225. 225 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Hull Cutoff Magnetic Equation

226. 226 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Hull Cutoff Voltage Equation

227. 227 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Cyclotron Angular Frequency

228. 228 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Cyclotron Angular Frequency

229. 229 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Time Period

230. 230 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Phase shift between adjacent cavities

231. 231 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Crossed Field tubes –M type

232. 232 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Phase constant

233. 233 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering π Mode

234. 234 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering RF Field

235. PH0101 Unit 2 Lecture 5 235 Working Fig (iv) Possible trajectory of electrons from cathode to anode in an eight cavity magnetron operating in  mode

236. PH0101 Unit 2 Lecture 5 236 Working The RF Oscillations of transient nature produced when the HT is switched on, are sufficient to produce the oscillations in the cavities, these oscillations are maintained in the cavities reentrant feedback which results in the production of microwaves. Reentrant feedback takes place as a result of interaction of the electrons with the electric field of the RF oscillations existing in the cavities. The cavity oscillations produce electric fields which fringe out into the interaction space from the slots in the anode structure, as shown in Fig (iv). Energy is transferred from the radial dc field to the RF field by the interaction of the electrons with the fringing RF field.

237. PH0101 Unit 2 Lecture 5 237 Working Due to the oscillations in the cavities, the either sides of the slots (which acts as a capacitor) becomes alternatively positive and negative and hence the directions of the electric field across the slot also reverse its sign alternatively. At any instant the anode close to the spiraling electron goes positive, the electrons gets retarded and this is because; the electron has to move in the RF field, existing close to the slot, from positive side to the negative side of the slot. In this process, the electron loses energy and transfer an equal amount of energy to the RF field which retard the spiraling electron. On return to the previous orbit the electron may reach the adjacent section or a section farther away and transfer energy to the RF field if that part of the anode goes positive at that instant.

238. PH0101 Unit 2 Lecture 5 238 Working This electron travels in a longest path from cathode to the anode as indicated by ‘a’ in Fig (iv), transferring the energy to the RF field are called as favoured electrons and are responsible for bunching effect and give up most of its energy before it finally terminates on the anode surface. An electron ‘ b ’ is accelerated by the RF field and instead of imparting energy to the oscillations, takes energy from oscillations resulting in increased velocity, such electrons are called unfavoured electrons which do not participate in the bunching process and cause back heating. Every time an electron approaches the anode “in phase” with the RF signal, it completes a cycle. This corresponds to a phase shift 2  . For a dominant mode, the adjacent poles have a phase difference of  radians, this called the  - mode.

239. PH0101 Unit 2 Lecture 5 239 Fig (v) Bunching of electrons in multicavity magnetron

240. PH0101 Unit 2 Lecture 5 240 Working At any particular instant, one set of alternate poles goes positive and the remaining set of alternate poles goes negative due to the RF oscillations in the cavities. AS the electron approaches the anode, one set of alternate poles accelerates the electrons and turns back the electrons quickly to the cathode and the other set alternate poles retard the electrons, thereby transferring the energy from electrons to the RF signal. This process results in the bunching of electrons, the mechanism by which electron bunches are formed and by which electrons are kept in synchronism with the RF field is called phase focussing effect . electrons with the fringing RF field.

241. PH0101 Unit 2 Lecture 5 241 Working The number of bunches depends on the number of cavities in the magnetron and the mode of oscillations, in an eight cavity magnetron oscillating with  - mode, the electrons are bunched in four groups as shown in Fig (v). Two identical resonant cavities will resonate at two frequencies when they are coupled together; this is due to the effect of mutual coupling. Commonly separating the pi mode from adjacent modes is by a method called strapping. The straps consist of either circular or rectangular cross section connected to alternate segments of the anode block.

242. PH0101 Unit 2 Lecture 5 242 Performance Characteristics Power output : In excess of 250 kW ( Pulsed Mode), 10 mW (UHF band), 2 mW (X band), 8 kW (at 95 GHz) Frequency : 500 MHz – 12 GHz Duty cycle : 0.1 % Efficienc y: 40 % - 70 %

243. PH0101 Unit 2 Lecture 5 243 Applications of Magnetron Pulsed radar is the single most important application with large pulse powers. Voltage tunable magnetrons are used in sweep oscillators in telemetry and in missile applications. Fixed frequency, CW magnetrons are used for industrial heating and microwave ovens.

244. 244

245. 245 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Mode Jumping

246. 246 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Mode Jumping Strapping Rising sun structure

247. 248 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Disadvantages They are costly and hence limited in use. Although cavity magnetron are used because they generate a wide range of frequencies , the frequency is not precisely controllable. The use in radar itself has reduced to some extent, as more accurate signals have generally been needed and developers have moved to klystron and systems for accurate frequencies.

248. 249 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Cross Field Amplifier

249. 250 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Cross Field Amplifier The Crossed-Field Amplifier (CFA), is a broadband microwave amplifier that can also be used as an oscillator ( Stabilotron ). It is a so called  Velocity-modulated Tube  . The CFA is similar in operation to the magnetron  and is capable of providing relatively large amounts of power with high efficiency. In contrast to the magnetron, the CFA have an odd number of resonant cavities coupled with each other. These resonant cavities work to as a slow-wave structure: an oscillating resonant cavity excites the next cavity. The actual oscillation will be lead from the input waveguide to the output waveguide . The electric and magnetic fields in a CFA are perpendicular to each other (“crossed fields”). Without an input signal and the influence of both the electric field (anode voltage) and the magnetic field (a strong permanent magnet) all electrons will move uniformly from the cathode to the anode on a cycloidal path as shown in figure

250. 251 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Cross Field Amplifier If the input-waveguide introduces an oscillation into the first resonator, the vanes of the resonator gets a voltage difference synchronously to the oscillation. Under the influence of this additionally field flying past electrons get acceleration (at the positively charged vane) or they are decelerated (at the negatively charged vane). This causes a difference in speed of the electrons. The faster electrons catch the slower electrons and the forms electron bunches in the interaction space between the cathode and the anode. These bunches of electrons rotates as like as the “Space-Charge Wheel” known from the magnetron operation. But they cannot rotate in full circle, the “Space-Charge Wheel” will be interrupted because the odd number of cavities causes an opposite phase in the last odd cavity (this bottom one between the waveguides). To avoid a negative feedback, into this resonant cavity may exist a bloc containing graphite to decouple input and output .

251. 252 National Institute of Technology, Warangal 9/2/2015 Microwave Engineering Cross Field Amplifier The bandwidth of the CFA, at any given instant, is approximately plus or minus 5 percent of the rated center frequency. Any incoming signals within this bandwidth are amplified. Peak power levels of many megawatts and  average power  levels of tens of kilowatts average are, with efficiency ratings in excess of 70 percent, possible with crossed-field amplifiers . To avoid ineffective modes of operation the construction of CFA contains  strapping wires  like to as used in magnetrons. Because of the desirable characteristics of wide bandwidth, high efficiency, and the ability to handle large amounts of power, the CFA is used in many applications in microwave electronic systems. When used as the intermediate or final stage in high-power radar systems, all of the advantages of the CFA are used.