Introduction to Antenna Analysis Using EM SimulationAnswers to RF Cafe Quiz #40
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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 Introduction to Antenna Analysis Using EM Simulation, by Hiroaki Kogure, Yoshie Kogure, and James C. Rautio. This book is also a great source of antenna fundamentals and a little communications history.
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1. What was the James C. Ratio's first antenna design program?
"The programs I wrote for those QST articles, called "Annie," is what got my company started. (see page xiii)
2. Just exactly is an antenna?
c) Any structure that performs the function of transmitting and receiving electromagnetic waves.
An antenna is usually made from metal pipe, conducting wire, or metal traces on a PCB. (see page 3)
3. Where is the approximate location of the near field / far field transition?
c) λ from the antenna
Up to about one wavelength around the antenna is called the near field. (see page 29)
4. What does a time-varying magnetic field generate?
a) An electric field
Faraday's law of induction, described in Chapter 1, states that "a time varying magnetic field generates an electric field." (see page 53)
5. What is the impedance of a minimum-loss coaxial cable with an air dielectric?
c) 75 Ω
When coax uses an air dielectric, we see minimum loss in the cable when we choose its dimensions so that the characteristic impedance (Z0) is about 75 ohms. When the coax is filled with a dielectric of relative permittivity of 2.55 (say, polyethylene), the minimum loss dimensions give a Z0 of about 50 ohms. (see page 88)
6. How is dielectric material modeled in an EM simulator?
b) Parallel RC
Dielectric material can be represented as an equivalent parallel RC circuit. The capacitor represents a lossless dielectric and the resistor represents dielectric loss. (see page 131)
7. What happens to magnetic flux if current through the loop is doubled?
a) It also doubles
Φ (flux) = L (inductance) * I (current). (see page 165)
8. For an input power of 1 W, what is the output power of a lossless passive antenna with a specified gain of 3 dB or 6 dB?
b) 1 W for both gains
An antenna with gain outputs more power in one direction and less power in another. If we look at the total power radiated in all directions, no extra power is created. (see page 200)
9. Where does a log-periodic antenna get its name?
d) From the logarithmic spacing and length ratios of its dipoles
A log-periodic antenna has different length dipoles whose spacings and lengths are determined by means of the logarithmic function. (see page 229)
10. Proper test environments are crucial to reliable EM field measurements as evidenced by what factor in Heinrich Hertz's early experiments?
d) A nearby pot-bellied stove
Hertz initially measured a wildly incorrect value for the speed of light in one of his early experiments. It turns out that the problem was a large cast iron stove located nearby in his laboratory. Effects of objects of any kind, including walls, earth, concrete, people, and so forth, can seriously disrupt measurements. (see page 203)
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