What are the effective aperture and directivity of both infinitesimal antennas and antennas of size lambda/2?
Understand the Problem
The question is asking for the concepts of effective aperture and directivity in relation to both infinitesimal antennas and antennas of size lambda/2. This involves understanding how these characteristics influence antenna performance.
Answer
λ/2 antenna: effective aperture λ^2/4π, directivity ~1.64. Infinitesimal antenna: low directivity ~1.5, negligible aperture.
For a λ/2 antenna, the effective aperture is λ^2/4π and its directivity is approximately 1.64 (2.15 dB). An infinitesimal dipole has very low directivity, around 1.5 (1.76 dB), and negligible effective aperture.
Answer for screen readers
For a λ/2 antenna, the effective aperture is λ^2/4π and its directivity is approximately 1.64 (2.15 dB). An infinitesimal dipole has very low directivity, around 1.5 (1.76 dB), and negligible effective aperture.
More Information
The effective aperture is the area over which an antenna can capture power from an incoming wavefront. Directivity is a measure of how 'focused' the radiation pattern of the antenna is compared to a uniform source.
Tips
Confusing effective aperture with physical size is common; focus on the ratio of captured power to power flux density. Directivity indicates focus of radiation, not gain.
Sources
- 10.13: Effective Aperture - Physics LibreTexts - phys.libretexts.org
- Antenna Basics - Mheducation - highered.mheducation.com
