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Navy Electricity and Electronics Training Series (NEETS)
Module 11—Microwave Principles
Chapter 2:  Pages 2-61 through 2-66




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.





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.

Tunnel diode curve

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.



Parametric amplifier



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.


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.



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.


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.


Introduction to Matter, Energy, and Direct Current, Introduction to Alternating Current and Transformers, Introduction to Circuit Protection, Control, and Measurement, Introduction to Electrical Conductors, Wiring Techniques, and Schematic Reading, Introduction to Generators and Motors, Introduction to Electronic Emission, Tubes, and Power Supplies, Introduction to Solid-State Devices and Power Supplies, Introduction to Amplifiers, Introduction to Wave-Generation and Wave-Shaping Circuits, Introduction to Wave Propagation, Transmission Lines, and Antennas, Microwave Principles, Modulation Principles, Introduction to Number Systems and Logic Circuits, Introduction to Microelectronics, Principles of Synchros, Servos, and Gyros, Introduction to Test Equipment, Radio-Frequency Communications Principles, Radar Principles, The Technician's Handbook, Master Glossary, Test Methods and Practices, Introduction to Digital Computers, Magnetic Recording, Introduction to Fiber Optics

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