# Coaching Materials in Microwave Communications Part 2 | ECE Board Exam

(Last Updated On: February 10, 2020)

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?

73. What is the result of an abrupt change in the size, shape, or dielectric of a waveguide?

74. A waveguide bend must have what minimum radius?

75. What is the most common type of waveguide 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?

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?

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?

84. Rotating the plane of polarization of a wavefront by passing it through a ferrite device is called what?

MICROWAVE COMPONENTS AND CIRCUITS

85. What is the primary advantage of bulk-effect devices over normal pn-junction semiconductors?

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?

87. The point on the current curve of a gallium-arsenide semiconductor at which it begins to exhibit negative resistance is called what?

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?

90. What is the junction arrangement of the original avalanche transit-time diode?

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?

92. What is the capacitive reactance across a point-contact diode as compared to a normal junction diode?

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?

95. The pin diode is primarily used for what purpose?

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 ___.

97. In microwave communications, what concepts may be used to analyze interference by obstacles near the path of a radio beam?

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 ____.

101. The IF bandwidth of a radar receiver is inversely proportional to the ________.

102. Carrier frequency 8 GHz and a distance 50 km. Determine FSL.

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?

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.

105. Find the cutoff wavelength of a waveguide with a dimension of 2 cm by 4 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.

108. Find the characteristic impedance of the waveguide used with a cutoff frequency of 3.75 GHz at a frequency of 5 GHz

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

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.

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?

140. Radar altimeters use what type of transmission signal?

Frequency Modulated (FM)

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