Which statement correctly describes a resonant antenna?

Which statement correctly describes a resonant antenna?

• A. It is centered around one frequency where it works at maximum efficiency.
• B. It is designed for a wide range of frequencies.
• C. It radiates uniformly in all directions.
• D. It has no impedance.

Answer: (A)

A resonant antenna is built so its length supports a standing wave at a specific frequency. When the electrical length matches a half-wavelength (or a multiple), the current distribution sets up a standing wave that minimizes reactive energy at the feed point. At that resonant frequency the input impedance becomes primarily real, so most of the power from the transmitter is radiated rather than stored in the near field. That’s why it operates with maximum efficiency at a centered frequency. This description captures the essential idea: resonance gives a peak in performance at one frequency because the reactive part of the impedance cancels. It’s not typically designed for a very wide range of frequencies, which is why the idea of broad, wideband operation isn’t the defining feature. The radiation pattern isn’t inherently uniform in all directions; the pattern depends on the antenna’s shape and arrangement, not just its resonance. And an antenna does have impedance—even at resonance the impedance is real (purely resistive) but still finite, not zero.

A resonant antenna is built so its length supports a standing wave at a specific frequency. When the electrical length matches a half-wavelength (or a multiple), the current distribution sets up a standing wave that minimizes reactive energy at the feed point. At that resonant frequency the input impedance becomes primarily real, so most of the power from the transmitter is radiated rather than stored in the near field. That’s why it operates with maximum efficiency at a centered frequency.

This description captures the essential idea: resonance gives a peak in performance at one frequency because the reactive part of the impedance cancels. It’s not typically designed for a very wide range of frequencies, which is why the idea of broad, wideband operation isn’t the defining feature. The radiation pattern isn’t inherently uniform in all directions; the pattern depends on the antenna’s shape and arrangement, not just its resonance. And an antenna does have impedance—even at resonance the impedance is real (purely resistive) but still finite, not zero.