This is the Coaching materials in Transmission Lines and Antennas Part 3 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.
Transmission Lines and Antennas Coaching Materials Part 3
101. in which plane will the half-wave antenna be operating if it is mounted horizontally?
102. Since the radiation pattern of a dipole is similar to that of a doublet, what will happen to the pattern if the length of the doublet is increased?
The pattern would flatten.
103. What is the simplest method of feeding power to the half-wave antenna?
To connect one end through a capacitor to the final output stage of the transmitter.
104. What is the radiation pattern of a quarter-wave antenna?
A circular radiation pattern in the horizontal plane, or same as a half-wave.
105. Describe the physical arrangement of a ground screen?
It is composed of a series of conductors arranged in a radial pattern and buried 1 to 2 feet below the ground.
106. What is the difference in the amount of impedance between a three-wire dipole and a simple-center fed dipole?
Nine times the feed-point impedance.
107. Which has a wider frequency range, a simple dipole, or a folded dipole?
108. What is the purpose of antenna stubs?
To produce desired phase relationship between connected elements
109. What is the primary difference between the major and minor lobes in a radiation pattern?
Major lobes have the greatest amount of radiation.
110. What is the maximum number of elements used in a collinear array?
111. Why is the number of elements in a collinear array limited?
As more elements are added, an unbalanced condition in the system occurs which impairs efficiency.
112. How can the frequency range of a collinear array be increased?
By increasing the lengths of the elements of the array.
113. How is directivity of a collinear array affected when the number of elements is increased?
114. What is the primary cause of broadside arrays losing efficiency when not operating at their designed frequency?
Lower radiation resistance
115. When more that two elements are used in a broadside array, how are the elements arranged?
Parallel and in the same plane.
116. As the spacing between elements in a broadside array increases, what is the effect on the major lobes?
117. What are some disadvantages of the end-fire array?
Extremely low radiation resistance, confined to one frequency, and affected by atmospheric conditions
118. Where does the major lobe in the end-fire array occur?
Along the major axis
119. To maintain the required balance of phase relationships and critical feeding, how must the end-fire array be constructed?
120. What two factors determine the directivity pattern of the parasitic array?
Length of the parasitic element (tuning) and spacing between the parasitic and driven elements.
121. What two main advantages of a parasitic array can be obtained by combining a reflector and a director with the driven element?
Increased gain and directivity.
122. The parasitic array can be rotated to receive or transmit in different directions. What is the name given to such an antenna?
123. What are the disadvantages of the parasitic array?
Their adjustment is critical and they do not operate over a wide frequency range.
124. What is the advantage of adding parasitic elements to a Yagi array?
125. The Yagi antenna is an example of what type of array?
Multi-element parasitic array
126. To radiate power efficiently, a long-wire antenna must have what minimum overall length?
127. What is another name for the Beverage antenna?
128. What is the polarity of the currents that feed the V antenna?
129. What is the main disadvantage of the rhombic antenna?
It requires a large antenna site.
130. What is the primary reason for the development of the turnstile antenna?
For omnidirectional vhf communications
131. Microwave antennas and low-frequency antennas are similar in what ways?
Operating principles and electrical characteristics
132. What term is used to express the efficiency of an antenna?
Power gain or power ratio.
133. What term is used to express the measurement of the degree of mismatch between a line and its load?
Standing-wave ratio (SWR)
134. What type of antenna radiates in and receives energy from all directions at once?
135. What is the term that is used to describe narrowness in the radiated beam of an antenna?
136. What characteristic allows the same antenna to both transmit and receive?
137. What type of reflector is most often used in directive antennas?
138. Microwaves can be reflected and focused in the same way as what other type of waves?
139. How many major lobes are radiated by a parabolic reflector?
140. A horizontally truncated parabolic antenna is used for what purpose?
141. The beam from a horizontally positioned cylindrical paraboloid is narrow in what plane?
142. What is a purpose of a collimating lens?
Forces the radial segments of a wavefront into parallel paths
143. What type of lens decelerates a portion of a spherical wavefront?
144. What is a set of antenna elements called?
145. What type of antenna has all elements connected to the same energy source?
146. What determines the beam elevation angle of an antenna that is electronically scanned in elevation?
Frequency or phase of radiated energy
147. What is the polarization of the energy radiated by a vertical slot?
148. Calculate the length of a half-wave dipole for an operating frequency of 20MHz.
149. A dipole antenna has a radiation resistance of 67 ohms and a loss resistance of 5 ohms measured at the feedpoint. Calculate the efficiency.
150. Determine the efficiency with the following: Pin = 1000w, I = 10 A, R = 8 ohm.