Resonant vs. Non-Resonant Antennas: Key Differences Explained

This page compares Resonant antennas and Non-Resonant antennas, highlighting the key differences between these two antenna types.

Resonant Antenna

Resonant antennas behave similarly to resonant transmission lines. Dipole antennas serve as a prime example of this type. They are open-ended with a resonant length, which refers to a multiple of a quarter wavelength.

Resonant antennas are typically positioned at a point on the transmission line that offers low impedance, usually a quarter wavelength ($\lambda/4$) from the open-circuit end.

Resonant Antenna

Figure 1 illustrates a half-wave dipole antenna and its radiation pattern, resembling a doublet.

Resonant Antenna radiation pattern

The radiation pattern of resonant antennas comprises two components: one due to the forward wave and the other due to the reflected wave. Figure 2 depicts these individual components, as well as the combined radiation pattern of a resonant antenna.

Non-Resonant Antenna

Non-resonant antennas, conversely, behave like non-resonant transmission lines. These lines are characterized by the absence of standing waves. Consequently, they exhibit no reflected waves, only forward traveling waves.

Non-resonant antenna and radiation pattern

When a non-resonant antenna is terminated (as illustrated in Figure 3, although the figure isn’t actually provided), approximately two-thirds (2/3) of the power is transmitted as forward waves. The remaining power is dissipated, and there is no reflected power returning toward the input.

Key Differences: Resonant vs. Non-Resonant Antennas

Based on the radiation patterns of both types, the core distinctions between resonant and non-resonant antennas are as follows:

• Non-resonant antennas are unidirectional, while resonant antennas are bi-directional.
• In non-resonant antennas, only forward waves exist. In resonant antennas, both forward and reflected waves are present.