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Consider the following statements: 1. The antennas radiate energy. 2. An antenna is a transition device or transducer between a guided wave and a free space wave or vice versa. 3. The resonators and transmission lines store energy. 4. An antenna converts electromagnetic signals to currents or vice versa. Which of these statements are correct?

Consider the following statements: 1. The antennas radiate energy. 2. An antenna is a transition device or transducer between a guided wave and a free space wave or vice versa. 3. The resonators and transmission lines store energy. 4. An antenna converts electromagnetic signals to currents or vice versa. Which of these statements are correct? Correct Answer 1, 2 and 4 only

Explanation:

An antenna is a transducer; that is, a device that converts signals in one form into another form.

In the case of an antenna, these two forms are:

(1) conductor-bound voltage and current signals and

(2) electromagnetic waves.

  • The Antenna radiates energy because in operation they all carry time-varying currents and, consequently, accelerating electrons. The dipole antenna is an example of a distributed circuit that owes its existence to the fact that it radiates well.
  • It is designed for the efficient conversion of electrical energy into radio waves.
  • But any system of conductors that carry varying currents behaves in accordance with the principles.
  • The same processes, including radiation, take place whether we call the system an antenna or something else. For example, what we generally refer to as reflection from a conducting surface (the radar dish, the ground) is actually radiation from free electrons set in motion by incident electric fields.

From the above explanation statements, 1,2, and 4 are satisfied hence they are true.

  • When one end of the waveguide is terminated in a shorting plate then reflections will occur and when another shorting plate is kept at a distance of a multiple of λ/2, then hollow space so formed can support a signal which bounces back and forth between the two shorting plates. This results in resonance and the hollow space is called cavity and the resonator as the cavity resonator. 
  • An electrical circuit composed of discrete components can act as a resonator when both an inductor and capacitor are included.
  • When a source of radio waves at one of the cavity's resonant frequencies is applied, the oppositely-moving waves form standing waves and the cavity stores electromagnetic energy.​
  • Whereas when a sinusoidal source is applied to the input of an ideal twin lead transmission line. The spacing between conductors is much less than a wavelength, and the output of the transmission line is terminated into an open circuit.
  • Hence no standing waves are formed and due to this transmission lines don't store energy.

 

So resonators store energy but transmission lines do not.

Hence statement 3 is false.

The solution is option 1.

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