Loading coils are a standard textbook method used to electrically lengthen physically short antennas, allowing them to operate efficiently.
The claim states that radio antennas much shorter than the wavelength can operate efficiently using loading coils. This is a foundational, well-established principle of radio antenna engineering (electrically small antennas using inductive loading). Because it is a basic engineering fact taught in standard electronics and physics curricula, it is classified as common knowledge and requires no specific paper citation.