Answers to RF Cafe Quiz #43
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All RF Cafe quizzes would make perfect fodder for employment interviews for technicians or engineers - particularly those who are fresh out of school or are relatively new to the work world. Come to think of it, they would make equally excellent study material for the same persons who are going to be interviewed for a job.
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Note: Many answers contain passages quoted in whole or in part from the text.
This quiz is based on the information presented in Plasma Antennas, by Theodore Anderson.
Note: Some of these books are available as prizes in the monthly RF Cafe Giveaway.
1. When the frequency of operation of a plasma antenna decreases, what is the corresponding requirement for plasma density?
c) Plasma density must decrease
A rule of thumb is that the plasma frequency should be about twice or greater than the operating frequency of the plasma antenna consider the plasma antenna to behave as an effective metal antenna. (see page 4)
2. How does plasma density affect signal phase during reflection and/or refraction?
c) Plasma density affected by both reflection and refraction
This property allows flat panel plasma tube arrays to be programmed as scanning phased arrays, adaptive parabolic, or just about any other shape antenna. (see page 5)
3. How is characteristic impedance controlled in a plasma antenna?
d) All the above
The text specifically cites the plasma density's role in affecting impedance, but the plasma antenna's shape and plasma material also determines impedance. (see page 34)
4. What commonly available component is useful as a plasma antenna demonstrator?
a) Fluorescent bulb
Probably the most useful fluorescent bulbs are the ones with a U shape that have electrode ends which can be placed inside a metal enclosure with only the glass tube exposed as an antenna.
(see page 38)
5. What is plasma, by the way?
b) An ionized gas
Duh. (see page 45)
6. In a multiple frequency nested plasma antenna, where is the highest frequency antenna element located relative to the lowest frequency antenna element?
b) Lowest frequency element on the outside, highest frequency element on the inside
Placing the denser, higher frequency at the innermost location and layering outward with progressively lower densities with correspondingly lower frequencies allows the inner layers to see through the outer layers (see page 47)
7. What is plasma "windowing?"
a) Creating electronically switched portal regions around an antenna array
Plasma regions can be made transparent or opaque to the radiating (or receiving) antenna inside the enclosure in order to shape the field beam. (see page 54)
8. What is a "smart" plasma antenna?
d) An antenna that use adaptive techniques to control beam patterns
Computer control can be used to determine angle of arrival, timestamp, and characterize signals, as well as do beam forming to target specific intended recipients. (see page 79)
9. How can plasma materials be used to provide filtering?
b) Layering regions of plasmas allows specific frequencies to be selected and others rejected
Each frequency-selective (FSS) layer has to be modeled using numerical methods and layers are stacked in such a way to create the desired filtering. (see page 113)
10. Who is undoubtedly the master of using commercial fluorescent tubes for constructing plasma devices like antennas, filters, and switches?
a) Theodore Anderson
Hands down. No question about it. (see entire book Plasma Antennas)
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