SESK: Stuff Everyone Should Know · sesk.info/hame-isotropic-radiator
What is an isotropic radiator?
A hypothetical, lossless antenna that radiates equally in all directions.
- A hypothetical lossless antenna radiating equally in all directions ✔
- A calibrated unidirectional antenna for gain measurements
- A spacecraft antenna aimed at Earth
Why: No real antenna is isotropic. Engineers use it as the reference when they state gain, such as dBi.
Huh, didn't know that: Ground gain is an increase in signal strength from ground reflections near the antenna (E9A05).
What did they call a monopole antenna when Marconi patented it? A monopoly antenna.
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References
Answer: A hypothetical lossless antenna radiating equally in all directions. No real antenna is isotropic. Engineers use it as the reference when they state gain, such as dBi.
- NCVEC 2024-2028 Amateur Extra Question Pool, 4th Errata (Feb 4, 2026) ncvec.org/downloads/2024-2028%20Extra%20Class%20Question%20Pool%20and%20Syllabus%20Public%20Release%20with%204th%20Errata%20Feb%204%202026.pdf
C. A hypothetical, lossless antenna having equal radiation intensity in all directions used as a reference
Checked 2026-10-11.
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