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> Radar Transmitter
Instructions to Student
Introduction - mm500580010
Lesson One Transmission Lines
First, a few terms.
Figure 2. Transmission Lines can be LONG or SHORT.
Types of transmission lines.
The parallel pair.
The coaxial line.
Review of transmission line types.
Figure 7. The Electrical Equivalent of a Transmission Line.
Why is characteristic impedance important?
Figure 8. The Infinitely Long Line.
Reflections occur when there is a sudden change in impedance.
Figure 9. Reflections are Due to Impedance Mismatches.
Figure 10. Formation of Standing Waves.
Standing waves are stationary.
Figure 11. Standing Waves Change in Amplitude But Do Not Move.
Review of standing waves on an open-end line.
Measuring standing waves.
Figure 14. Measuring Standing Waves of Voltage.
Figure 15. Measuring the Standing-Wave Ratio.
Figure 16. Measuring Standing Waves of Current.
Figure 17. Impedance Variations Along a Shorted Transmission Line.
A section of transmission line acts like a resonant circuit.
Figure 20. Quarter-Wave Line Applications.
The half-wave section of transmission line.
Figure 21. Voltage, Current and Impedance Variations on a Half-Wave Section of Transmission Line.
Figure 22. Half-Wave Line Applications.
Transmission lines other than one-quarter or one-half wavelength.
Learning Event 2: Artifical Transmission lines
Characteristic impedance and characteristic resistance.
Transmission lines delay voltage.
An ATL can be substituted for a real line.
Radar systems need rectangular pulses.
Figure 26. Double "L" Section ATL and Equivalent Circuit.
Figure 27. Double "L" Section ATL.
Figure 28. The 50-Volt Pulse Travels Along the ATL.
The reflected wave travels toward the battery.
Determining the time delay.
Figure 30. Discharge Path Connected to ATL.
A discharging ATL is used in radar modulators.
Charge and discharge waveforms when Rc equals RL.
Figure 33. Waveforms of PFN.
When Rc does not equal Rch or RL in a PFN.
Figure 35. Rc less than RL.
Figure 37. Rc greater than RL.
Delay lines are used in synchroscopes.
Delay lines are used in time division multiplexing.
Figure 41. Block Diagram of Multiplexing Delay Line.
How the delay line works in a TDM transmitter.
Practice Exercise - mm500580059
Practice Exercise - Continued - mm500580060
Practice Exercise - Continued - mm500580061
Figure 42. Section of Transmission Line.
Figure 43. Quarter-Wave Section Transmission Line.
Figure 44. Shorted Quarter-Wave Stub Impedance.
Figure 45. Sections of an ATL.
Figure 46. Pulse-Forming Network.
Figure 47. Artificial Transmission Line.
Situation - mm500580068
Figure 49. Charging ATL.
Figure 50. Network to Form Rectangular Pulse.
Figure 51. Pulse-Forming Network Waveforms.
Lesson Two High - Level Modulation
Figure 52. Basic Radar Transmitter.
Learning Event 2: High - Level Modulation
Figure 53. How High-Level Modulation Works.
Learning Event 3: The PFN
Learning Event 3: The PFN - Continued
Brief review. - mm500580078
Learning Event 4: Hydrogen Thyratron Switch
Figure 56. Early Radar Sets Used Spark Gaps to Discharge the PFN.
Figure 57. Construction of 5C22 thyratron.
Figure 58. The HYDROGEN THYRATRON is an Electronic Switch.
Brief review. - mm500580083
DC resonant charging circuit.
DC resonant charging circuit. - Continued
Charging diode prevents discharge of PFN.
Figure 62. DC Resonant Charging Circuit With Holding Diode.
Learning Event 6: The Pulse Transformer
Pulse transformer windings.
Brief review. - mm500580092
Learning Event 7: Magnetron Impedance
Learning Event 8: Reverse-Current Diode
Figure 67. Review of High-Level Modulation.
Learning Event 9: The Discharge Cycle
Learning Event 10: Troubleshooting High-Level Modulators
Trouble symptom. No modulator output pulse.
Final Summary. - mm500580100
Final Summary. - Continued
Practice Exercise (Performance-Oriented) - mm500580102
Practice Exercise (Performance-Oriented) - Continued - mm500580103
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Situation - mm500580105
Figure 70. Radar Transmitter Schematic.
Practice Exercise (Performance-Oriented) - Continued - mm500580107
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Practice Exercise (Performance-Oriented) - Continued - mm500580110
Lesson Three. Resonant Cavities and Magnetrons
Figure 71. Resonant Cavities are Used at Microwave Frequencies.
Transmission line sections are used as resonant circuits.
Figure 73. Development of Resonant Cavity.
Some characteristics of resonant cavities.
Different forms can be used.
A brief review.
The PRIMARY mode of operation.
Figure 76. PRIMARY Mode of Oscillation During First Half Cycle.
The main points to remember about the fields of a resonant cavity.
Figure 78. Tuning Methods.
First, plunger tuning.
Summary of tuning methods.
Figure 79. Loop Coupling Compared to Transformer Coupling.
Summary of coupling methods.
How you use the echo box.
A magnetron contains resonant cavities.
Final summary. - mm500580130
Learning Event 2: Magnetrons
The outside construction of a magnetron.
Figure 86. Outside View of Typical Magnetrons.
Brief review on magnetron construction.
All oscillators need regeneration.
Electron flow in diode tube.
Reaction of one magnetic field on another magnetic field.
A permanent magnet can also move electrons in a diode.
Strength of magnet and cathode voltage determine electron path.
Now change the cathode voltage.
Electrons that strike the anode excite the cavities.
Segments are strapped to ensure correct polarity.
Figure 94. How the RF Fields are Reinforced.
Summarizing electron movement.
Summary of magnetron operation.
Figure 95. Never Drop or Hit a Magnet.
Measuring magnet flux.
Operating a new magnetron.
Troubleshooting the magnetron.
Causes of faulty operation beyond the antenna.
Other magnetron troubles.
Final summary. - mm500580154
Figure 98. Typical Operating Values of Magnetrons.
Glossary of magnetron terms.
Practice Exercise - mm500580157
Practice Exercise - Continued - mm500580158
Figure 99. Resonant Cavity.
Figure 100. Resonant Cavity Output Connection.
Figure 101. Magnetron Cavity Resonator.
Figure 102. Magnetrons.
The combination of the electric and magnetic fields
Figure 103. Electron Motion in a Magnetron.
The filament starting voltage for a QK324 magnetron is 4.8 volts
Figure 104. Regenerative Electrons.
If the RF output of a magnetron is pulled off frequency
Lesson Four - Antennas and Waveguides
Figure 105. Typical Waveguide.
Characteristics of a shorted quarter-wavelength section.
Making a guide for RF energy from two-wire line and quarter-wave stubs.
Figure 109. Dimensions of Waveguide Determine Power and Frequency.
A brief summary.
Figure 110. The E and H Fields Inside a Resonant Cavity and a Waveguide.
Summing up waveguide field characteristics.
Why waveguide has very low loss due to skin effect.
Why waveguide does not have radiation loss.
Energy is usually coupled into waveguide with a probe.
Figure 113. Probe Coupling into a Waveguide.
Figure 115. Waveguide Coupled to a Reflector.
Coupling waveguide to test equipment.
Reviewing methods of coupling energy from a waveguide.
Round waveguide used as rotating choke joint.
Fixed rectangular joints.
Waveguide bends guide RF energy around corners.
What are E and H bends?
Next, flexible waveguide.
Methods of tuning waveguide.
Fixed window tuner.
Complete system of RF components.
Learning Event 2: Radar Antennas
Accuracy depends on antenna directivity and width of radar beam.
An antenna radiates or picks up energy.
Polarization of a dipole antenna.
Directivity and radiation pattern.
Adding a reflector to the dipole makes the antenna directional.
Adding a director also makes dipole antenna directional.
Dipole with director and reflector.
Summarizing main points so far.
How energy is coupled to a radar antenna.
Antenna radiation pattern is called a beam.
A narrow horizontal beam gives accurate azimuth information.
A narrow vertical beam gives accurate height information.
The main points to remember about radar beams.
Radar reflectors work like light reflectors.
How a dish reflector works.
A section of a dish reflects energy in a fan-shaped pattern.
Radar set AN/MPQ-10 uses a dish reflector.
Radar set 4N/SPN-5 uses an orange peel reflector.
Radar set AN/TPS-1D also uses an orange peel reflector.
Radar set AN/FPN-33 uses an orange peel reflector mounted vertically.
Radar set AN/MPQ-4A antenna uses a parabolic cylinder.
Summary of parabolic reflector antennas.
Metallic lens antennas.
Figure 153. Comparison of Action of Glass Lens to That of Metallic Lens.
The M-33 tracking radar uses a metallic lens antenna.
Reflector feed systems.
Figure 155. Front Feed System.
Figure 156. Tapered Horn.
Figure 158. Sectoral Horn.
Figure 160. Rear Feed With a Splash Plate.
Practice Exercise (Performance-Oriented) - mm500580231
Practice Exercise (Performance-Oriented) - Continued - mm500580232
Figure 166. Waveguide Fittings.
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Figure 167. Radar Antenna System.
Practice Exercise Lesson Solutions
Practice Exercise Lesson Solutions - Continued
Lesson 2: High-Level Modulation
Lesson 3: Resonant Cavities and Magnetrons
Lesson 3: Resonant Cavities and Magnetrons - Continued - mm500580243
Lesson 3: Resonant Cavities and Magnetrons - Continued - mm500580244
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