Define beamwidth and explain how antenna aperture influences it.

Define beamwidth and explain how antenna aperture influences it.

• A. Beamwidth is the angular width of the main lobe; approximate 3-dB beamwidth θ ≈ k λ / D; larger aperture D yields narrower beam and better angular resolution.
• B. Beamwidth is the angular width of the main lobe; θ ≈ D / (k λ); larger aperture D yields narrower beam.
• C. Beamwidth is the angular width of the side lobes; θ ≈ k λ / D; larger aperture D yields wider beam.
• D. Beamwidth is the total angular span of the pattern; θ ≈ λ / D^2.

Answer: (A)

Beamwidth is the angular width of the main lobe of the antenna’s radiation pattern, indicating how directional the antenna is. In practice, for a finite aperture, the main lobe width scales inversely with the aperture size and directly with the wavelength. A commonly used approximation for the 3-dB beamwidth is θ ≈ k λ / D, where D is the effective aperture diameter and λ is the wavelength; k is a constant that depends on the exact aperture shape and how beamwidth is defined (often around a value close to 1). This means that increasing the aperture size makes the main lobe narrower, reducing θ and improving angular resolution, so the antenna can distinguish signals coming from closer angles. The other formulations don’t fit the established relationship. They either suggest that a larger aperture widens the beam, or they reference the pattern in terms of side lobes rather than the main lobe, or they give a scaling like λ / D^2 which isn’t supported by the standard Fourier-optics view of aperture radiation.

Beamwidth is the angular width of the main lobe of the antenna’s radiation pattern, indicating how directional the antenna is. In practice, for a finite aperture, the main lobe width scales inversely with the aperture size and directly with the wavelength. A commonly used approximation for the 3-dB beamwidth is θ ≈ k λ / D, where D is the effective aperture diameter and λ is the wavelength; k is a constant that depends on the exact aperture shape and how beamwidth is defined (often around a value close to 1). This means that increasing the aperture size makes the main lobe narrower, reducing θ and improving angular resolution, so the antenna can distinguish signals coming from closer angles.

The other formulations don’t fit the established relationship. They either suggest that a larger aperture widens the beam, or they reference the pattern in terms of side lobes rather than the main lobe, or they give a scaling like λ / D^2 which isn’t supported by the standard Fourier-optics view of aperture radiation.