What is a resonant antenna?

What is a resonant antenna?

• A. An antenna centered around one frequency where it works at maximum efficiency.
• B. An antenna designed for a wide range of frequencies.
• C. An anisotropic antenna.
• D. An isotropic antenna.

Answer: (A)

Resonance in an antenna means it is optimized to operate at a single frequency where the current distribution forms a standing wave and the energy stored in the near field is minimized relative to what is radiated. At that frequency the reactive part of the input impedance cancels out, leaving a predominantly resistive impedance that matches the feed and allows maximum power transfer. A half-wavelength dipole is a classic example—about λ/2 long, it supports a strong standing wave along the conductor with efficient radiation at the center. When you move away from the resonant frequency, reactance grows, the current pattern changes, and both efficiency and bandwidth tend to drop. This is why a resonant antenna is described as being centered around one frequency with maximum efficiency. The other terms refer to different concepts—wideband operation and radiation patterns like isotropic or anisotropic—not to resonance itself.

Resonance in an antenna means it is optimized to operate at a single frequency where the current distribution forms a standing wave and the energy stored in the near field is minimized relative to what is radiated. At that frequency the reactive part of the input impedance cancels out, leaving a predominantly resistive impedance that matches the feed and allows maximum power transfer. A half-wavelength dipole is a classic example—about λ/2 long, it supports a strong standing wave along the conductor with efficient radiation at the center. When you move away from the resonant frequency, reactance grows, the current pattern changes, and both efficiency and bandwidth tend to drop. This is why a resonant antenna is described as being centered around one frequency with maximum efficiency. The other terms refer to different concepts—wideband operation and radiation patterns like isotropic or anisotropic—not to resonance itself.