Antenna Theory and Design

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Questions and Answers

What is the effect of constructing a similar antenna on the other side of the conducting sheet?

  • It will reduce the antenna's performance
  • It will improve the antenna's performance
  • It will change the polarity of the antenna
  • It will not affect the antenna's performance in any way (correct)

What is the effect of removing the conducting sheet in the arrangement equivalent to the Hertz antenna?

  • It will reduce the antenna's performance
  • It will not have any effect (correct)
  • It will improve the antenna's performance
  • It will change the polarity of the antenna

How does the drive point impedance of the Hertz antenna compare to the Marconi antennas?

  • It is half as great
  • It is the same
  • It is four times as great
  • It is twice as great (correct)

How does the power absorbed by the Hertz antenna compare to the Marconi antennas?

<p>It is twice as much (A)</p> Signup and view all the answers

What is the relationship between the currents in the Marconi antennas and the Hertz antenna?

<p>The currents are the same (D)</p> Signup and view all the answers

What is the purpose of the conducting sheet in the Marconi antenna arrangement?

<p>The conducting sheet has no purpose and can be removed without effect (D)</p> Signup and view all the answers

How is radiation achieved in the antenna setup?

<p>By opening out the conductors and having currents in the same direction (D)</p> Signup and view all the answers

What is a half-wave dipole?

<p>Two arms with a total length slightly less than half a wavelength (B)</p> Signup and view all the answers

Which of the following statements about the half-wave dipole is true?

<p>It serves as a useful reference standard against which other antennas can be compared (C)</p> Signup and view all the answers

What does the voltage and current detector measure?

<p>The electric and magnetic fields around the conductors (A)</p> Signup and view all the answers

What is the relationship between the magnetic field and the current in the conductor?

<p>The magnetic field is directly proportional to the current (D)</p> Signup and view all the answers

What does the demonstration with the two conductors show?

<p>It shows the production of expanded fields stretching away from the conductors (A)</p> Signup and view all the answers

What is the primary function of a transmission line in a radio system?

<p>To convey power from the transmitter to the antenna (C)</p> Signup and view all the answers

Why is it important that the voltage and current on a transmission line be 'suitably balanced'?

<p>To prevent the transmission line from radiating power (C)</p> Signup and view all the answers

What is the purpose of the 'feeders' mentioned in the text?

<p>To connect the transmitter or receiver to the antenna (B)</p> Signup and view all the answers

Why does the voltage and current vary at different points along a transmission line?

<p>Due to the inductance and capacitance of the line (D)</p> Signup and view all the answers

What is the purpose of properly designing a transmission line?

<p>To minimize radiation from the line (C)</p> Signup and view all the answers

What is the simplest case of connecting a transmitter or receiver to an antenna?

<p>Directly connecting the terminals (D)</p> Signup and view all the answers

What is the purpose of using half-wave and quarter-wave rods with lamps inserted at intervals?

<p>To demonstrate the effects of capacitance and inductance on current distribution (C)</p> Signup and view all the answers

What is the primary difference between the T antenna and the inverted-L antenna demonstrated?

<p>The T antenna produces more vertically polarized radiation, while the inverted-L produces more horizontally polarized radiation (D)</p> Signup and view all the answers

What is the primary benefit of using loading techniques when the antenna height is limited in relation to the wavelength?

<p>It increases the radiation resistance, reducing power losses (B)</p> Signup and view all the answers

What happens to the drive point impedance and radiation resistance when the electrical length of an antenna is changed?

<p>The drive point impedance and radiation resistance change, but the effects can be beneficial (B)</p> Signup and view all the answers

What is the primary cause of power losses in short antennas?

<p>High currents due to low radiation resistance (D)</p> Signup and view all the answers

Which of the following statements is true about the demonstrations described in the text?

<p>They focus on the effects of capacitance and inductance on antenna performance (B)</p> Signup and view all the answers

What is the purpose of the impedance transformation over a /4 feeder in an antenna?

<p>To determine the impedance ratio and the rate of change of reactance with frequency in the antenna (D)</p> Signup and view all the answers

What is the 'characteristic impedance' of an antenna defined as?

<p>$Z_o = \sqrt{(maximum R_d)(radiation resistance)}$ (B)</p> Signup and view all the answers

How can the characteristic impedance $Z_o$ of an antenna be altered?

<p>Both (b) and (c) (C)</p> Signup and view all the answers

What is the expression that can be used to calculate the characteristic impedance $Z_o$ for a vertical round wire just above a perfectly conducting ground?

<p>$Z_o = \left(\ln\left(\frac{h}{r}\right) - 1\right)$ (C)</p> Signup and view all the answers

What is the distinction between radiation resistance and the drive point impedance of an antenna?

<p>Radiation resistance is defined at the point of maximum current, while drive point impedance is defined at the feed point (B)</p> Signup and view all the answers

What is the typical range of values for the characteristic impedance $Z_o$ of a vertical round wire antenna just above a perfectly conducting ground?

<p>Between 230 and 650 ohms (B)</p> Signup and view all the answers

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