Module 11 − Microwave Principles
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.
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.
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.
electron will be accelerated.
A-7. By alternately speeding up or slowing down the electrons.
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-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-20. The reflector or repeller.
A-23. Mode 2.
A-24. Power is reduced.
A-25. The half-power points of the mode.
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-32. a magnetic field.
A-33. Anode or plate.
A-34. The resonant cavities.
A-36. The critical value of field strength.
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-43. Working electrons.
A-44. Greater power output.
A-45. Loops and slots.
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.
feedback to the tuned input circuit.
A-53. Stability problems.
A-54. Variable capacitor.
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
A-60. The pump signal of a nondegenerative parametric amplifier is higher than twice the input
A-61. Idler- or lower-sideband frequency.
A-62. The sum of the input frequency and the
A-63. Larger microwave power outputs.
A-64. The electrons become immobile.
A-66. a field of much greater intensity.
A-67. The frequency.
A-69. The negative-resistance property.
A-70. To form a small region of
A-72. Lower forward resistance and low noise.
A-74. a switching device.
and Direct Current
||Alternating Current and Transformers
||Circuit Protection, Control, and Measurement
||Electrical Conductors, Wiring Techniques,
and Schematic Reading
||Generators and Motors
||Electronic Emission, Tubes, and Power Supplies
||Solid-State Devices and Power Supplies
||Wave-Generation and Wave-Shaping Circuits
||Wave Propagation, Transmission Lines, and
||Introduction to Number Systems and Logic Circuits
||- Introduction to Microelectronics
||Principles of Synchros, Servos, and Gyros
||Introduction to Test Equipment
||Radio-Frequency Communications Principles
||The Technician's Handbook, Master Glossary
||Test Methods and Practices
||Introduction to Digital Computers
||Introduction to Fiber Optics
|Note: Navy Electricity and Electronics Training
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