Radio and TV Engineering ECE 151 Lecture 2: Antenna Fundamentals
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Questions and Answers

What is the measure of an antenna's directivity?

  • Effective radiated power
  • Radiation pattern
  • Antenna gain
  • Beam width (correct)

    • How is the beam width of an antenna measured?

  • Between the points on the radiation curve that are 15 dB down from the maximum amplitude
  • Between the points on the radiation curve that are 10 dB down from the maximum amplitude
  • Between the points on the radiation curve that are 6 dB down from the maximum amplitude
  • Between the points on the radiation curve that are 3 dB down from the maximum amplitude (correct)

    • How is antenna gain usually expressed?

  • As a ratio of the effective radiated output power to the input power
  • In decibels (correct)
  • In watts
  • In milliwatts

    • What is the impedance of a dipole antenna at its center?

    <p>73 Ω</p> Signup and view all the answers

    What is the purpose of the insulators in a wire dipole antenna?

    <p>To support the wire elements</p> Signup and view all the answers

    What is the purpose of the transmission line in a dipole antenna?

    <p>To provide power to the antenna</p> Signup and view all the answers

    What happens when a radio wave encounters a perfect conductor?

    <p>Total reflection occurs</p> Signup and view all the answers

    Which type of surfaces can cause reflection of radio waves?

    <p>Metallic and partially conductive surfaces</p> Signup and view all the answers

    What happens to a radio wave when it encounters a good conductor?

    <p>Most of the wave is reflected</p> Signup and view all the answers

    What causes refraction of a radio wave?

    <p>Changes in air density</p> Signup and view all the answers

    What is the effect of a poor conductor on a radio wave?

    <p>Absorbs some of the wave energy</p> Signup and view all the answers

    How does the degree of bending of a radio wave during refraction relate to the medium's index of refraction?

    <p>Directly proportional</p> Signup and view all the answers

    What is the reason a radio signal is called an electromagnetic wave?

    <p>It consists of both electric and magnetic fields.</p> Signup and view all the answers

    In a wire antenna, what happens when voltage is applied?

    <p>Electric field is set up and current flows, producing a magnetic field.</p> Signup and view all the answers

    How are the electric and magnetic fields emitted from the antenna?

    <p>At right angles to each other.</p> Signup and view all the answers

    What do transmission lines, unlike antennas, not efficiently do?

    <p>Radiate radio signals.</p> Signup and view all the answers

    What happens to the direction of the electric field between wires in a transmission line during one-half cycle of the ac input?

    <p>The direction reverses once per cycle.</p> Signup and view all the answers

    How does the strength of a magnetic field produced by a wire antenna relate to the strength of an electric field produced?

    <p>They are both expressions of different field strengths.</p> Signup and view all the answers

    What is the index of refraction for air?

    <p>Very close to 1</p> Signup and view all the answers

    What happens when an incident wave from a transmitter travels through air and meets a region of ionized air?

    <p>The speed of propagation slows down, and the wave is bent (refracted).</p> Signup and view all the answers

    What is Snell's law related to?

    <p>The relationship between the angles and the indices of refraction when a wave is refracted.</p> Signup and view all the answers

    What is a shadow zone?

    <p>A region where some of the signal is blocked by an obstacle between the transmitter and receiver.</p> Signup and view all the answers

    What is the main signal path for radio signals in the 30-kHz to 3-MHz range?

    <p>Ground waves</p> Signup and view all the answers

    What type of polarization is required for ground waves to be propagated from an antenna?

    <p>Vertical polarization</p> Signup and view all the answers

    Which of the following layers of the ionosphere are weakly ionized and exist only during daylight hours?

    <p>D and E layers</p> Signup and view all the answers

    What is the primary effect of the F layer on radio signals?

    <p>Causing refraction of radio signals when they cross boundaries with different ionization levels</p> Signup and view all the answers

    What happens when a radio signal goes into the ionosphere?

    <p>It is gradually bent due to different levels of ionization</p> Signup and view all the answers

    Which statement is true about radiation directly vertical from the antenna?

    <p>It passes through the ionosphere</p> Signup and view all the answers

    What happens to radio signals at very high frequencies above about 50 MHz?

    <p>Refraction seldom occurs regardless of the angle</p> Signup and view all the answers

    What is the result of reflected radio waves being sent back to Earth with minimum signal loss?

    <p>The signal is propagated over an extremely long distance</p> Signup and view all the answers

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