This is the Coaching materials in Microwave Communications Part 2 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 2
71. What is the primary purpose of a dummy load?
Answer: Absorb all energy without producing standing waves
72. The energy dissipated by a resistive load is most often in what form?
Answer: Heat
73. What is the result of an abrupt change in the size, shape, or dielectric of a waveguide?
Answer: Reflections
74. A waveguide bend must have what minimum radius?
Answer: Greater than 2 wavelengths
75. What is the most common type of waveguide joint?
Answer: Choke joint
76. What is the most likely cause of losses in waveguide system?
Answer: Improperly connected joints or damaged inner surface
77. What is the primary purpose of a directional coupler?
Answer: Sampling energy within a waveguide
78. How far apart are the two holes in a simple directional coupler?
Answer: ¼ wavelength
79. What two variables determine the primary frequency of a resonant cavity?
Answer: Size and shape of the cavity
80. Energy can be inserted or removed from a cavity by what three methods?
Answer: Probes, Loops, and Slots
81. Inductive tuning of a resonant cavity is accomplished by placing a nonmagnetic slug in what area?
Answer: The area of maximum H lines
82. Ferrite devices are useful in microwave applications because they possess what properties?
Answer: Magnetic properties and high resistance
83. Which of the two types of electron motion (orbital movement and electron spin) is more important in the explanation of magnetism?
Answer: Electron spin
84. Rotating the plane of polarization of a wavefront by passing it through a ferrite device is called what?
Answer: Faraday rotation
MICROWAVE COMPONENTS AND CIRCUITS
85. What is the primary advantage of bulk-effect devices over normal pn-junction semiconductors?
Answer: Larger microwave power outputs
86. What happens to the electrons of a gallium-arsenide semiconductor when they move from the normal low-energy conduction band to the high-energy conduction band?
Answer: The electrons become immobile
87. The point on the current curve of a gallium-arsenide semiconductor at which it begins to exhibit negative resistance is called what?
Answer: Threshold
88. The domain in a gallium-arsenide semiconductor has what type of electrical field when compared to the other regions across the body of a semiconductor?
Answer: A field of much greater intensity
89. What characteristic of a gunn oscillator is inversely proportional to the transit time of the domain across the semiconductor?
Answer: Frequency
90. What is the junction arrangement of the original avalanche transit-time diode?
Answer: pnin
91. What causes dc bias energy to be absorbed by avalanche electrons and given up to the microwave field applied to an avalanche transit-time diode?
Answer: the negative-resistance property
92. What is the capacitive reactance across a point-contact diode as compared to a normal junction diode?
Answer: lower
93. What are the most important advantages of the Schottky barrier diode?
Answer: lower forward resistance and low noise
94. At frequencies above 100 MHz, the intrinsic (i) region causes a pin diode to act as what?
Answer: variable resistance
95. The pin diode is primarily used for what purpose?
Answer: a switching device
96. The microwave tube that is a linear beam tube, in which the interaction between the beam and the RF field is continuous, is the ___.
Answer: traveling wave tube
97. In microwave communications, what concepts may be used to analyze interference by obstacles near the path of a radio beam?
Answer: Fresnel zone
98. The scope of radar system displays ___.
Answer: target range, but not position *
99. Blind speed solution is to
Answer: vary the pulse repetitive rate
100. The band using frequency in the band of 27-40 GHz is ____.
Answer: ka
101. The IF bandwidth of a radar receiver is inversely proportional to the ________.
Answer: pulse width
102. Carrier frequency 8 GHz and a distance 50 km. Determine FSL.
Answer: 144.48 dB
103. Calculate the effective radiated power (ERP) of a repeater with 200 W transmitting power output, 1 dB feedline loss, 3 dB duplexer loss, 3 dB circulator loss, and feedline antenna gain of 10 dB?
Answer: 398 W
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104. Find the cutoff frequency for the TE10 mode in an air-dielectric waveguide with an inside cross section of 2 cm by 4 cm.
Answer: 3.75 GHz
105. Find the cutoff wavelength of a waveguide with a dimension of 2 cm by 4 cm.
Answer: 8 cm
106. Find the cutoff wavelength of a circular waveguide with an internal radius of 2 cm and a Bessel constant kr = 1.84
Answer: 0.068 m or 6.8 cm
107. Find the group velocity for the waveguide with a cutoff frequency of 3.75 GHz and operating at 5 GHz.
Answer: 198 x 10^6 m/s
108. Find the characteristic impedance of the waveguide used with a cutoff frequency of 3.75 GHz at a frequency of 5 GHz
Answer: 570 ohms
109. Find the guide wavelength for the waveguide used with a phase velocity of 454 x 10^6 m/s at a frequency of 5 GHz
Answer: 9.08 cm
110. A microwave communication uses plane reflector as passive repeaters. The diameter of the parabolic antenna is 18 ft., while the effective area is 310 ft^2. Determine the reflector coupling factor.
Answer: 0.906
RADAR
111. Radar surface-angular measurements are referenced to true north and measured in what plane?
Horizontal Plane
112. The distance from a radar set to a target measured along the line of sight is identified by what term?
Range
113. How much time is required for electromagnetic energy to travel 1 nautical mile and return to the source?
12.36 microseconds
114. In addition to recovery time, what determines the minimum range of a radar set?
Pulse width
115. Atmospheric interference with the travel of electromagnetic energy increases with what rf energy characteristic?
Frequency
116. How is prt related to prf?
1/prt = prf
117. What type of radar transmitter power is measured over a period of time?
Average Power
118. What term is used to describe the product of pulse width and pulse-repetition frequency?
Duty Cycle
119. What type of target bearing is referenced to your ship?
Relative bearing
120. What type of radar detects range, bearing, and height?
Three-dimensional
121. What characteristic/s of radiated energy is/are altered to achieve electronic scanning?
Frequency or phase
122. What term is used to describe the ability of a radar system to distinguish between targets that are close together?
Target resolution
123. The degree of bearing resolution for a given radar system depends on what two factors?
Beam width and range
124. What happens to the speed of electromagnetic energy traveling through air as the altitude increases?
Speed increases
125. What term is used to describe a situation in which atmospheric temperature first increases with altitude and then begins to decrease?
Temperature inversion
126. What radar subsystem supplies timing signals to coordinate the operation of the complete system?
Synchronizer
127. What radar component permits the use of a single antenna for both transmitting and receiving?
Duplexer
128. What is the simplest type of scanning?
Single lobe
129. What are the two basic methods of scanning?
Mechanical and electronic
130. Rotation of an rf-feed source to produce a conical scan pattern is identified by what term?
Nutation
131. The Doppler effect causes a change in what aspect of rf energy that strikes a moving object?
Frequency
132. The Doppler variation is directly proportional to what radar contact characteristic?
Velocity
133. The Doppler method of object detection is best for what type of objects?
Fast-moving targets
134. The beat frequency in a swept-frequency transmitter provides what contact information?
Range
135. What factor determines the difference between the transmitted frequency and the received frequency in an FM transmitter?
Travel Time
136. What type of objects are most easily detected by an FM system?
Stationary
137. What transmission method does NOT depend on relative frequency or target motion?
Pulse Modulation
138. What transmission method uses a stable CW reference oscillator, which is locked in phase with the transmitter frequency?
Pulse-Doppler
139. What type of radar provides continuous range, bearing, and elevation data on an object?
Track Radar
140. Radar altimeters use what type of transmission signal?
Frequency Modulated (FM)
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