Beam Width

Beam width (also referred to as beamwidth or half-power beam width) defines the angular spread of an antenna’s main radiation lobe. It is a critical parameter for characterizing an antenna’s directivity, coverage area, and spatial selectivity in wireless, radar, and satellite communication systems.

E-plane and H-plane Beam Widths

Beam width is typically measured in two orthogonal planes:

• E-plane Beam Width: The angular width of the main lobe in the plane defined by the electric field and the direction of maximum radiation (often the vertical plane).

• H-plane Beam Width: The angular width of the main lobe in the plane defined by the magnetic field and the direction of maximum radiation (typically the horizontal plane).

These measurements help characterize how an antenna radiates in space and are crucial for directional antenna design.

Relationship to Directivity

Beam width and directivity are inversely related. Narrower beams focus energy more tightly, increasing antenna directivity. An approximate formula for directivity D in linear terms is:

D ≈ 4π / (θ_E × θ_H)

Where:

• θ_E = E-plane beam width (in radians)

• θ_H = H-plane beam width (in radians)

This relationship illustrates that as beam width decreases, the antenna becomes more directional.

Physical Estimation Methods

Beam width can be estimated based on physical antenna dimensions:

θ ≈ λ / d

Where:

• λ = Wavelength of the signal

• d = Aperture dimension (e.g., diameter of a parabolic reflector)

Larger apertures result in narrower beam widths, enabling long-range, focused signal transmission.

Example: Real-World Beam Width Values

• Cellular Base Station Antenna:
  Horizontal beam width ≈ 65°
  Vertical beam width ≈ 7°
  → Enables sectorized coverage with controlled interference.

• Satellite Dish (1 m diameter at 12 GHz):
  Beam width ≈ 1.5°
  → Allows high-gain, long-range communication with precise alignment.

Applications and Design Trade-offs

Beam width plays a central role in antenna and system design:

• Narrow Beam Width:

  • High gain and long-range capability

  • Requires precise alignment

  • Used in point-to-point links, radar, and satellite systems

• Wide Beam Width:

  • Broad area coverage

  • Lower gain and increased interference susceptibility

  • Suitable for broadcast and mobile base station antennas

Designers must trade off between coverage area, interference control, system complexity, and alignment precision.