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Module 11 - Microwave Principles |
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Module 11 − Microwave Principles
Pages i, 1−1, 1−11, 1−21, 1−31, 1−41, 1−51, 1−61, 2−1, 2−11, 2−21, 2−31, 2−41, 2−51, 2−61, 3−1, 3−11, AI−1, Index−1, Assignment 1, Assignment 2
The TWT is a wide-bandwidth, velocity-modulated tube used primarily as an amplifier. The electron beam is bunched by a signal applied to the Helix. The bunching causes an energy transfer from the electron beam to the traveling wave on the helix. The MAGNETRON is a DIODE Oscillator capable of delivering microwave energy at very high power levels. Three fields exist within a magnetron that influence operation: (1) the DC ELECTRIC FIELD between the anode and cathode; (2) the AC ELECTRIC FIELD produced by the oscillating resonant cavities and on the same plane as the dc field; and (3) the Magnetic FIELD produced by the permanent magnet which is perpendicular to the dc electric field. Magnetrons are of two basic types, the Negative-Resistance MAGNETRON and the ELECTRON-RESONANCE MAGNETRON. a diagram of a magnetron is shown at the right.
2-61
SOLID-STATE Microwave DEVICES are becoming increasingly widespread in microwave equipment with new developments almost daily. Most of the currently available solid-state devices are two-terminal diodes with the capability to generate or amplify microwave energy. Many of the solid-state devices, such as the TUNNEL DIODE and the BULK-EFFECT DIODE, apply the property of Negative Resistance to amplify microwave signals or generate microwave energy. a characteristic curve illustrating the negative-resistance property of the tunnel diode is shown at the right.
The VARACTOR is a two-terminal diode that acts as a variable capacitance and is the active element of PARAMETRIC AmplifierS. The parametric amplifier is a low-noise microwave amplifier that uses variable reactance to amplify microwave signals. The illustration shows an example of a NONDegenerative PARAMETRIC Amplifier. 2-62
Answers to Questions Q1. Through Q74.
A-1. Impedance decreases. A-2. Degenerative feedback. A-3. Transit time causes the grid voltage and plate current to be out of phase. A-4. Transit time. A-5. Velocity. A-6. The electron will be accelerated. A-7. By alternately speeding up or slowing down the electrons. A-8. The buncher grids. A-9. There is no effect. A-10. The frequency period of the buncher grid signal. A-11. Velocity modulation.
2-63 A-12. The accelerator grid and the buncher grids. A-13. The catcher cavity. A-14. Amplifier. A-15. Intermediate cavities between the input and output cavities. A-16. a large negative pulse is applied to the cathode. A-17. The middle cavity. A-18. The bandwidth decreases. A-19. Stagger tuning. A-20. The reflector or repeller. A-21. Velocity. A-22. Three-quarter cycle. A-23. Mode 2. A-24. Power is reduced. A-25. The half-power points of the mode. A-26. Voltage amplification. A-27. used to focus the electrons into a tight beam. A-28. The directional couplers are not physically connected to the helix. A-29. The traveling wave must have a forward velocity equal to or less than the speed of the electrons in the beam. A-30. The helix. A-31. Helix. A-32. a magnetic field. A-33. Anode or plate. A-34. The resonant cavities. A-35. The permanent magnet. A-36. The critical value of field strength. A-37. Circular. A-38. The negative-resistance magnetron has a split plate. A-39. The application of the proper magnetic field.
2-64 A-40. To reduce the effects of filament bombardment. A-41. Rising-sun block. A-42. Series. A-43. Working electrons. A-44. Greater power output. A-45. Loops and slots. A-46. Inductive. A-47. a cookie-cutter tuner. A-48. Baking in. A-49. The tunneling action. A-50. The tuned circuit or cavity frequency. A-51. To increase the stability. A-52. Prevent feedback to the tuned input circuit. A-53. Stability problems. A-54. Variable capacitor. A-55. Reactance. A-56. The low-noise characteristic. A-57. By varying the amount of capacitance in the circuit. A-58. Supplies the electrical energy required to vary the capacitance. A-59. Exactly double the input frequency. A-60. The pump signal of a nondegenerative parametric amplifier is higher than twice the input signal. A-61. Idler- or lower-sideband frequency. A-62. The sum of the input frequency and the pump frequency. A-63. Larger microwave power outputs. A-64. The electrons become immobile. A-65. Threshold. A-66. a field of much greater intensity. A-67. The frequency. 2-65 A-68. PNIN. A-69. The negative-resistance property. A-70. To form a small region of p-type material. A-71. Lower. A-72. Lower forward resistance and low noise. A-73. Variable resistance. A-74. a switching device. 2-66
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