All RF Cafe Quizzes make great 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.
1. What does dBi, the most often used unit for antenna gain (or directivity), stand for?
c)
Decibels of gain relative to an isotropic radiator
An isotropic radiator is theoretically a point source
(dimensionless), and therefore distributes the input power uniformly across the entire spherical volume
surrounding it. Directivity concentrates the input power in a preferred direction, leaving less power to be
radiated in the not-preferred directions.
2. For which region of space does antenna gain normally apply?
b) Far field
Almost
without exception, specified antenna gain refers to the far field. The common sense proof is that if you had two
antennas with a gain of, say, 10 dBi, and placed them face-to-face, you would not realize a gain of 20 dB in
signal power while the path loss would be negligible. One exception would be NFC (near field communications)
antennas which are designed to use combinations of inductive and/or magnetic coupling to transfer the signal.
Elevation Pattern Azimuth Pattern
3. For which type of antenna does the pattern to the right describe? c) 1/2-wave dipole
5. What is the
name given to the point where the RF input signal interfaces to the antenna?
b) Feed-point
This is
where the signal conductors physically attach to the antenna's radiating element structure.
6.
Where is the approximate transition point between near field and far field?
a) λ / (2p)
The
explanation is a bit complex, so please see this link on the
Conformity site for details.
7. What is an isotropic radiator?
a) An antenna that radiates equally in all directions
See Q1.
8. Which type of antenna would typically have the highest directivity?
d) Parabolic
Depending on the size, degree of curvature, and the edge properties of the parabolic dish, gain (directivity,
which is generally interchangeable with gain for high efficiencies) can be very high.
See Antenna
Patterns page for gain ranges of various antenna types.
9.
On a center-fed 1/2-wave dipole, where is the voltage potential the highest?
b) At the tips (see diagram to
right).
Intuitively, at the tips of the antenna the current has nowhere to flow, so I = 0 there. The
1/2-wave dipole acts like a capacitor where the voltage lags the current by 90°. As a result, the voltage is at
maximum magnitude at the tips.
10.
Yagi antennas are constructed of which three types of elements?
c) Reflector, driven, and director
The Yagi, or Yagi-Uda, is constructed similar to the one shown to the right. One or more reflector elements are
behind the driven element, and one or more director elements are in front of the driven element. Design your
own at the
DXZone website.
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