Start here: The Chu–Harrington limit describes a fundamental lower bound on Q for an antenna confined to a given small sphere at a specified electrical size.
Why this changes a real station
It explains why an electrically small passive antenna faces severe bandwidth and efficiency tradeoffs; it does not predict the exact performance of every practical antenna.
What it looks like in practice
A commercial “wideband” claim cannot repeal the size limit—it may rely on loss, active circuitry, multiple modes, or a different performance criterion.
What to do next
Compare the actual enclosing size, frequency, efficiency, bandwidth definition, and matching method before invoking the limit.
Evidence boundary
Keep frequency, reference plane, antenna geometry, losses, measurement method, and safety conditions attached to the conclusion. A match, a DC check, or one field symptom does not prove efficiency or identify the complete RF path.
