A dipole antenna is cut and bent to achieve efficient radiation. The total length of the wire used as the dipole is equal to half a wavelength (i.e., l=λ/2）.This type of antenna is called a half-wave dipole antenna. Due to its advantages, it is the most widely used antenna, and is also known as the Hertz antenna.
Frequency Range
The half-wave dipole antenna operates over a frequency range of approximately 3 kHz to 300 GHz, and is primarily used in radio receivers.
Structure and Operating Principle of a Half-Wave Dipole
It is a basic dipole antenna whose operating frequency corresponds to half the wavelength; therefore, it is called a half-wave dipole antenna.
The ends of the dipole have maximum voltage, which is alternating current (AC) in nature. At the positive peak of the voltage, electrons tend to move in one direction, while at the negative peak, they move in the opposite direction. This can be explained with the help of the figure below.
The figure above illustrates the operating principle of a half-wave dipole.
Figure 1 shows the dipole when it is in the positive half‑cycle of the induced voltage. At this moment, electrons tend to move toward the positive charge.
Figure 2 shows the dipole in the negative half-cycle of the induced voltage. Here, electrons tend to move away from the dipole.
Figure 3 shows the dipole in the next positive half‑cycle. At this point, electrons again move toward the charge.
This cumulative effect generates a varying electromagnetic field, which radiates outward in the same pattern as that produced on the dipole itself. Consequently, the output of the antenna is an effective radiation that follows the periodic pattern of the output voltage. In this way, the half-wave dipole achieves efficient radiation.
The figure above shows the current distribution in a half-wave dipole. The gain of a half-wave dipole is 2.15 dBi, which is quite good. Here, the letter “i” refers to an isotropic radiator.
Radiation mode
The radiation pattern of this half-wave dipole antenna is omnidirectional in the H-plane, making it suitable for a wide range of applications such as mobile communications and radio reception.
The figure above shows the radiation patterns of a half-wave dipole in the H-plane and V-plane.
For a dipole with a length of half a wavelength (i.e., the first resonant length), its radius does not affect the input impedance. The antenna operates most efficiently at its resonant frequency, which occurs at its resonant length.
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Post time: Jun-05-2026
