What are the differences between resonant and non-resonant antennas?

Resonant antennas are tuned to specific frequencies, efficient at those points, have pure resistance but narrow bandwidth. Non-resonant antennas work across wide bands (traveling waves), need matching networks (tuners) for efficiency, have reactive impedance, and are less efficient at single points but good for multiband use.

Resonant antennas operate at their natural resonant frequency, where length is a half-wavelength (λ/2) or quarter-wavelength (λ/4). Impedance is purely resistive at the resonant frequency, making matching to a transmission line simpler. They have narrow bandwidth centered around the resonant frequency. They have high efficiency at resonance due to good impedance match, minimal reflections, and standing waves. Examples are half-wave dipole and quarter-wave monopole antennas.

Non-resonant antennas operate off-resonance, often as traveling wave antennas with current moving in one direction. They have reactive (capacitive or inductive) impedance, requiring an antenna tuner for matching. Non-resonant antennas have wide bandwidth and are suitable for multiband operation. But their efficiency can be less at specific points due to mismatch, yet good overall for broad coverage. Examples are long wire antennas, random wire antennas and rhombic antennas.