TRUE/FALSE
1. Antennas are considered to be active devices.
ANS: F
2. Any antenna can transmit a signal as well as receive one.
ANS: T
3. A half-wave dipole is an isotropic radiator.
ANS: F
4. The "gain" of an antenna is often given as its performance relative to a half-wave dipole.
ANS: T
5. A half-wave dipole is sometimes called a "Hertz" antenna.
ANS: T
6. A "Hertzian Dipole" is a theoretical concept and not a real antenna.
ANS: T
7. A half-wave dipole is actually 5% longer than half a wavelength.
ANS: F
8. A half-wave dipole radiates uniformly in all directions.
ANS: F
9. The horizontal radiation pattern of a half-wave dipole is symmetrical front and back.
ANS: T
10. Compared to a point-source radiator, a half-wave dipole has gain.
ANS: T
11. A half-wave dipole does not have directivity.
ANS: F
12. In general, the near-field radiation pattern of an antenna is not the same as its far-field radiation pattern.
ANS: T
13. The front-to-back ratio of a dipole is 0 dB.
ANS: T
14. Antenna gain given in dBd is gain relative to a half-wave dipole.
ANS: T
15. The input impedance of an antenna at resonance is infinity.
ANS: F
16. A center-fed dipole antenna is a balanced load.
ANS: T
17. The input impedance of a center-fed dipole increases as the separation between the cable connections is increased.
ANS: T
18. The polarization of a dipole antenna is always horizontal.
ANS: F
19. A folded dipole has a wider bandwidth than a simple dipole.
ANS: T
20. A folded dipole has a higher input impedance than a simple dipole.
ANS: T
21. There is actually no such thing as a "monopole" antenna.
ANS: F
22. Vertical antennas typically need a ground plane.
ANS: T
23. The earth itself can be a ground plane.
ANS: T
24. The sheet-metal body of a car can be a ground plane.
ANS: T
25. A helical antenna cannot receive vertically polarized radio waves.
ANS: F
26. A helical antenna cannot receive horizontally polarized radio waves.
ANS: F
27. A typical helical antenna can receive either clockwise or counterclockwise circularly polarized waves, but not both.
ANS: T
28. An antenna must be resonant at the frequency it is transmitting or receiving.
ANS: F
29. A nonresonant antenna can cause a high SWR in the transmission line connected to it.
ANS: T
30. Any antenna will transmit radio waves as long as an RF current is flowing in it.
ANS: T
31. A "loading coil" is used to make an antenna appear longer to a signal than its physical length.
ANS: T
32. Antennas cannot be made to appear shorter to a signal than their actual physical length.
ANS: F
33. A phased array is a driven array.
ANS: T
34. A Yagi array is a "parasitic" array.
ANS: T
35. A Yagi array is unidirectional.
ANS: T
36. A Log-Periodic Dipole array is a "parasitic" array.
ANS: F
37. A Log-Periodic Dipole array is unidirectional.
ANS: T
38. A Turnstile array is unidirectional.
ANS: F
39. Stacked Yagis form a phased array.
ANS: T
40. A parabolic "dish" can be a reflector.
ANS: T
41. A flat piece of metal can be a reflector.
ANS: T
42. A piece of sheet metal bent at a 90° angle can be a reflector.
ANS: T
43. A piece of thin metal tubing can be a reflector.
ANS: T
44. Only certain types of antennas, such as "horns", can be used with a parabolic reflector.
ANS: F
45. An anechoic chamber requires highly reflective surfaces.
ANS: F
MULTIPLE CHOICE
1. The real part of an antenna's input impedance is due to:
| a. | the radiated signal | c. | the SWR |
| b. | the reflected signal | d. | all of the above |
ANS: A
2. A half-wave dipole is sometimes called:
| a. | a Marconi antenna | c. | a Yagi antenna |
| b. | a Hertz antenna | d. | none of the above |
ANS: B
3. The end-to-end length of a half-wave dipole antenna is actually:
| a. | one wavelength | c. | slightly longer than a half-wavelength |
| b. | one half-wavelength | d. | slightly shorter than a half-wavelength |
ANS: D
4. The radiation of energy from an antenna can be seen in the:
| a. | standing wave pattern around the antenna | c. | radiation resistance of the antenna |
| b. | SWR along the feed cable | d. | I2R loss of the antenna |
ANS: C
5. Measured on the ground, the field strength of a horizontally polarized half-wave dipole antenna is strongest:
| a. | in one direction | c. | in all directions |
| b. | in two directions | d. | depends on the number of elements |
ANS: B
6. The ability of an antenna to radiate more energy in one direction than in other directions is called:
| a. | directivity | c. | active antenna |
| b. | selectivity | d. | resonance |
ANS: A
7. The front-to-back ratio of a half-wave dipole antenna is:
| a. | 0 dB | c. | 10 dB |
| b. | 3 dB | d. | infinite |
ANS: A
8. An antenna's beamwidth is measured:
| a. | from +90° to –90° | c. | between half-power points |
| b. | from front to back | d. | between the minor side-lobes |
ANS: C
9. ERP stands for:
| a. | Equivalent Radiation Pattern | c. | Equivalent Radiated Power |
| b. | Effective Radiation Pattern | d. | Effective Radiated Power |
ANS: D
10. "Ground Effects" refers to the effects on an antenna's radiation pattern caused by:
| a. | radio signals reflecting off the ground |
| b. | buildings and other structures on the ground |
| c. | fading |
| d. | faulty connection of the feed cable ground |
ANS: A
11. A 1-MHz monopole antenna must be:
| a. | mounted vertically | c. | at least one half-wavelength long |
| b. | mounted horizontally | d. | at least one wavelength long |
ANS: A
12. The typical antenna in an AM radio is a:
| a. | dipole | c. | ferrite "loop-stick" |
| b. | folded dipole | d. | none of the above |
ANS: C
13. The polarization of plane waves received from a satellite is changed by:
| a. | gamma rays | c. | helical rotation |
| b. | Faraday Rotation | d. | the distance traveled |
ANS: B
14. A nonresonant antenna:
| a. | will not transmit | c. | will cause SWR on the feed cable |
| b. | will not receive | d. | all of the above |
ANS: C
15. At resonance, the input impedance to a lossless antenna should be:
| a. | resistive | c. | capacitive |
| b. | inductive | d. | infinite |
ANS: A
16. An antenna can be matched to a feed line using:
| a. | a shorted stub | c. | an LC network |
| b. | a loading coil | d. | all of the above |
ANS: D
17. As the length of a "long-wire" antenna is increased:
| a. | the number of lobes increases | c. | efficiency decreases |
| b. | the number of nodes decreases | d. | none of the above |
ANS: A
18. Arrays can be:
| a. | phased | c. | parasitic |
| b. | driven | d. | all of the above |
ANS: D
19. An array with one driven element, a reflector, and one or more directors is called a:
| a. | Marconi | c. | Log-Periodic Dipole |
| b. | Yagi | d. | stacked array |
ANS: B
20. LPDA stands for:
| a. | Low-Power Dipole Array | c. | Log-Periodic Dipole Array |
| b. | Low-Power Directed Array | d. | Log Power Dipole Array |
ANS: C
21. The radiated beam from a parabolic "dish" transmitting antenna is:
| a. | collimated | c. | dispersed |
| b. | phased | d. | none of the above |
ANS: A
22. The energy picked up by a parabolic antenna is concentrated at the:
| a. | center | c. | focus |
| b. | edges | d. | horn |
ANS: C
23. Antennas are often tested in:
| a. | an echo chamber | c. | a vacuum chamber |
| b. | an anechoic chamber | d. | an RF reflective chamber |
ANS: B
24. Field strength at a distance from an antenna is measured with:
| a. | a slotted line | c. | an EIRP meter |
| b. | a dipole | d. | a field-strength meter |
ANS: D
COMPLETION
1. An antenna is the interface between the transmission line and ____________________.
ANS: space
2. Hertz antenna is another name for a half-wave ____________________.
ANS: dipole
3. The length of a half-wave dipole is about ____________________ % of a half-wave in free space.
ANS: 95
4. The ____________________ resistance is the portion of an antenna's input impedance due to transmitted radio waves leaving the antenna.
ANS: radiation
5. Input impedance at the center feed point of a resonant half-wave dipole is about ____________________ W.
ANS: 70
6. Input impedance at the center feed point of a resonant folded dipole is about ____________________ W.
ANS: 280 – 300
7. The vertical angle of radiation is called the angle of ____________________.
ANS: elevation
8. Antenna radiation patterns are typically drawn on graphs with ____________________ coordinates.
ANS: polar
9. As compared to a ____________________ source, a half-wave dipole has a gain of about 2 dBi.
ANS:
point
isotropic
10. Antenna gain measured in ____________________ is with reference to a half-wave dipole.
ANS: dBd
11. ____________________ is the same as the gain for a lossless antenna.
ANS: Directivity
12. The front-to-back ratio of a half-wave dipole is ____________________ dB.
ANS: 0
13. The ____________________ of a directional antenna is the angle between its half-power points.
ANS: beamwidth
14. ERP stands for ____________________ radiated power.
ANS: effective
15. ERP is the power input to the antenna multiplied by the antenna's ____________________.
ANS: gain
16. A ____________________ is required to connect a coaxial cable to a center-fed dipole antenna.
ANS: balun
17. A horizontally mounted dipole will radiate waves with ____________________ polarization.
ANS: horizontal
18. A folded dipole has ____________________ bandwidth than a standard dipole.
ANS:
wider
greater
more
19. A monopole antenna is typically mounted in the ____________________ direction.
ANS: vertical
20. The length of a typical monopole antenna is ____________________ wavelength.
ANS:
one-quarter
1/4
21. A monopole antenna mounted high on a tower typically uses a ____________________ plane.
ANS: ground
22. A vertical antenna has an _________________________ radiation pattern for ground-based receivers.
ANS: omnidirectional
23. The number of driven elements in a Yagi antenna is typically ____________________.
ANS: one
24. The reflector on a Yagi antenna is called a ____________________ element.
ANS: parasitic
25. An LPDA is a ____________________ dipole array.
ANS: log-periodic
26. If an LPDA had five elements, the number of driven elements it had would be ____________________.
ANS: five
27. All the waves that hit the surface of a parabolic antenna merge at the ____________________.
ANS: focus
28. A ____________________ beam has all its individual rays parallel to each other.
ANS: collimated
29. A microwave ____________________ antenna is essentially an extension of a waveguide.
ANS: horn
30. An ____________________ chamber is often used to test microwave antennas.
ANS: anechoic
SHORT ANSWER
1. Calculate the physical length of a half-wave dipole for use at 300 MHz.
ANS:
475 millimeters
2. How much power will a 95% efficient antenna radiate if driven with 100 watts?
ANS:
95 watts
3. If an antenna has 10.14 dB of gain compared to a point source, how much gain does it have compared to a half-wave dipole?
ANS:
8 dB
4. What is the ERP of an antenna with 10 dBd of gain and driven by one watt?
ANS:
10 watts
5. A resonant antenna has an input impedance of 100 ohms and is driven by 100 watts. What is the RMS current in the antenna?
ANS:
1 ampere
6. A resonant antenna has an input impedance of 100 ohms and is driven by 100 watts. What is the RMS voltage at the feed-point of the antenna?
ANS:
100 volts
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