This is the Coaching materials in Microwave Communications Part 1 as one topic in ECE Board Exam taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies (EST), Communications Books, Journals and other Communications References. This particular Coaching Notes in Communications Engineering has random Questions and Answers in random topics. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.
Microwave Communications Coaching Materials Part 1
1. Which is a possible polarization for an electromagnetic wave:
Answer: Circular *
2. Which polarization can be reasonably well received by a circularly polarized antenna:
Answer: Circular *
3. The number of circular polarization modes (directions) is:
Answer: 2 *
4. When an EM wave propagates in free space, it travels as a ___.
5. An antenna has "gain" as compared to:
Answer: an isotropic radiator
6. Ground waves are most effective:
Answer: below about 2 MHz *
7. Band most suitable for SSB operation
Answer: 3-30 MHz
8. Frequency band used with submarine
9. The SHF range of frequency:
Answer: 3 – 30 GHz
10. Sky waves cannot be heard:
Answer: in the “skip” zone *
11. A 20-dB reduction in the strength of a radio wave due to reflection is called:
Answer: Fading *
12. “Ghosts” on a TV screen are an example of:
Answer: multipath distortion
13. Frequency band most suitable for LOS propagation:
14. The troposphere is the:
Answer: lowest layer of the atmosphere
15. The cumulative sum of the direct, ground-reflected, and surface waves is referred to as ____.
Answer: Ground wave
16. It is an earth-guided electromagnetic wave that travels over the surface of the earth
Answer: Surface wave
17. ________ travels essentially in a straight line between the transmit and the receive antennas
Answer: Direct waves
18. The curvature of the Earth presents a horizon to space wave propagation commonly called ___.
Answer: Virtual Height
19. It is the height above Earth’s surface from which a reflected wave appears to have been reflected.
Answer: Virtual Height
20. It is the highest frequency that can be used for sky wave propagation between two specific points on Earth’s surface
Answer: Maximum Usable Frequency
21. 85 percent of the maximum usable frequency (MUF) is called ____.
Answer: Optimum Working Frequency (OWF)
22. It is defined as the minimum distance from the transmit antenna that a sky wave at a given frequency will be returned to earth.
Answer: Skip distance
23. At distances greater than the skip distance, two rays can take different paths and still be returned to the same point on Earth. The two rays are called lower rays and
Answer: Pedersen ray or upper ray
24. The area between where the surface waves are completely dissipated and the point where the first sky wave returns to earth is called
Answer: Quiet zone or Skip zone
25. It is defined as the loss incurred by an electromagnetic wave as it propagates in a straight line through a vacuum with no absorption or reflection of energy from nearby objects
Answer: Free-space path loss
26. For a carrier frequency of 6 GHz and a distance of 50 km, determine the free-space path loss
Answer: 142 dB
27. The propagation velocity of longitudinal waves depends on the ___ of the medium
28. Bending of radio waves from high density to low density
29. Only layer exist at night
30. Most dense of all the ionized layer of ionosphere
31. Present only during daytime
32. “Beyond the horizon” propagation
33. Radiation occurring on frequencies which are whole or multiple of the original desired frequencies is called
Answer: harmonic radiation
34. The velocity of radio waves ___ as it passes from air to the ionosphere.
35. Ducts often are formed over
Answer: bodies of water
36. Meteor-trail propagation is
Answer: used to send data by radio *
37. It states that every point on a given spherical wavefront can be considered as a secondary point source of electromagnetic waves from which other secondary waves or wavelets are radiated outward.
Answer: Huygen’s principle
38. Electromagnetic waves traveling within Earth’s atmosphere is called ____.
Answer: Terrestrial wave
39. What is the region of the frequency spectrum from 1000 MHz to 100,000 MHz called?
Answer: Microwave region
40. Microwave theory is based upon what concept
Answer: Electromagnetic field theory
41. What kind of material must be used in the construction of waveguides?
Answer: Conductive Material
42. What causes the current-carrying area at the center conductor of a coaxial line to be restricted to a small layer at the surface?
Answer: Skin effect
43. What is used as a dielectric in waveguides?
44. What is the primary lover-frequency limitation of waveguides?
Answer: Physical size
45. At very high frequencies, what characteristics are displayed by ordinary insulators?
Answer: The characteristics of the dielectric of a capacitor
46. What type of insulator works well at very high frequencies?
Answer: A shorted quarter-wave section called a metallic insulator
47. The frequency range of a waveguide is determined by what dimension?
Answer: The “a” dimension
48. What happens to the bus bar dimensions of the waveguide when the frequency is increased?
Answer: The bus bar becomes wider
49. When the frequency is decreased so that two quarter-wavelengths are longer than the “a” (wide) dimension of the waveguide, what will happen?
Answer: Energy will no longer pass through the waveguide
50. What interaction causes energy to travel down a waveguide?
Answer: The interaction of the electric and magnetic fields
51. What is indicated by the number of arrows (closeness of spacing) used to represent an electric field?
Answer: The relative strength of the field
52. What primary condition must magnetic lines of force meet in order to exist?
Answer: Magnetic lines of force must form a continuous closed loop
53. What happens to the H lines between the conductors of a coil when the conductors are close together?
Answer: The H lines cancel
54. For an electric field to exist at the surface of a conductor, the field must have what angular relationship to the conductor?
Answer: The field must be perpendicular to the conductors
55. Assuming the wall of a waveguide is perfectly flat, what is the angular relationship between the angle of incidence and the angle of reflection?
Answer: The angles are equal
56. What is the frequency called that produces angles of incidence and reflection that are perpendicular to the waveguide walls?
Answer: Cutoff Frequency
57. Compared to the velocity of propagation of waves in air, what is the velocity of propagation of waves in waveguides?
58. What term is used to identify the forward progress velocity of wavefronts in a waveguide?
Answer: Group velocity
59. What term is used to identify each of the many field configurations that can exist in waveguides?
Answer: Mode of Operation
60. What field configuration is the easiest to produce in a given waveguide?
Answer: Dominant mode
61. How is the cutoff wavelength of a circular waveguide figured?
Answer: 1.71 times the diameter
62. The field arrangements in waveguides are divided into what two categories to describe the various modes of operation?
Answer: Transverse electric (TE) and Transverse magnetic (TM)
63. The electric field is perpendicular to the “a” dimension of a waveguide in what mode?
64. What determined the frequency, bandwidth, and power-handling capability of a waveguide probe?
Answer: Size and shape
65. Loose or inefficient coupling of energy into or out of a a waveguide can be accomplished by the use of what method?
Answer: Slots and apertures
66. What is used to construct irises?
Answer: Metal plates
67. An iris placed along the “b” dimension wall produces what kind of reactance?
68. How will an iris that has portions along both the “a” and “b” dimension walls act at the resonant frequency?
Answer: As a shunt resistance
69. What device is used to produce a gradual change in impedance at the end of a waveguide?
70. When a waveguide is terminated in a resistive load, the load must be matched to what property of the waveguide?
Answer: Characteristic Impedance