This chapter discusses the parameters of antenna radiation beams, which help us understand beam specifications.
Beam Area
According to the standard definition: “If the radiation intensity P(θ,ϕ) remains at its maximum value over a solid angle ΩA and is zero elsewhere, then the beam area is the solid angle through which all the power radiated by the antenna passes.”
The radiated beam from an antenna is emitted within a certain solid angle where the radiation intensity is maximum. This solid beam angle is called the beam area and is denoted by ΩA.
Within this solid angle ΩA, the radiation intensity P(θ,ϕ) should be constant and maximum, and zero elsewhere. Therefore, the total radiated power is given by:
Radiated Power=P(θ,ϕ)⋅ΩA(watts)
The beam angle generally refers to the solid angle between the half‑power points of the main lobe.
Mathematical Expression
The mathematical expression for the beam area is:
where the differential solid angle is:
dΩ=sinθdθdϕ
Here, Pn(θ,ϕ) is the normalized radiation intensity.
• ΩA represents the solid beam angle (beam area).
• θ is a function of the angular position.
• ϕ is a function of the radial distance.
Unit
The unit of beam area is the steradian (sr).
Beam Efficiency
According to the standard definition: “Beam efficiency is the ratio of the beam area of the main beam to the total radiated beam area.”
The energy radiated by an antenna depends on its directivity. The direction in which the antenna radiates the most power has the highest efficiency, while some energy is lost in side lobes. The ratio of the maximum radiated energy in the main beam to the total radiated energy, with minimal loss, is called beam efficiency.
Mathematical Expression
The mathematical expression for beam efficiency is:
where
• ηB is the beam efficiency (dimensionless),
• ΩMB is the solid angle (beam area) of the main beam,
• ΩA is the solid angle of the total radiated beam.
Antenna Polarization
Antennas can be designed with different polarizations according to application requirements, such as linear or circular polarization. The type of polarization determines the beam characteristics and polarization state of the antenna during reception or transmission.
Linear Polarization
When an electromagnetic wave is transmitted or received, its direction of propagation may vary. A linearly polarized antenna keeps the electric field vector confined to a fixed plane, thereby concentrating energy in a specific direction while suppressing other directions. Hence, linear polarization helps improve antenna directivity.
Circular Polarization
In a circularly polarized wave, the electric field vector rotates over time, with its orthogonal components being equal in amplitude and 90° out of phase, resulting in no fixed direction. Circular polarization effectively mitigates multipath effects and is therefore widely used in satellite communications, such as GPS.
Horizontal Polarization
Horizontally polarized waves are more susceptible to reflection from the Earth’s surface, causing signal attenuation, especially at frequencies below 1 GHz. Horizontal polarization is commonly used for television signal transmission to achieve a better signal-to-noise ratio.
Vertical Polarization
Vertically polarized low-frequency waves are advantageous for ground wave propagation. Compared to horizontal polarization, vertically polarized waves are less affected by surface reflections and are therefore widely used in mobile communications.
Each polarization type has its own advantages and limitations. RF system designers can freely choose the appropriate polarization according to specific system requirements.
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Post time: Apr-24-2026
