The HIRF frequency spectrum is divided in three frequency bands: Low Frequency (LF: 10 kHz 50 MHz) band, Medium Frequency (MF: 30 MHz 400 MHz) band and High Frequency (HF: 100MHz 18/40 GHz) band.
Each frequency band produces different electromagnetic field distributions around and inside an aircraft. In the LF band, the aircraft acts like an antenna and the electromagnetic field penetration into the fuselage is weak, while in the HF band, strong field penetration into the fuselage is seen.
In the MF band, both effects antenna like behaviour and field penetration are superimposed. External fields in the LF and MF band induce currents on the fuselage skin. These may couple into cable harnesses and, as a result, into the aircraft electronics themselves.
The field that penetrates into the fuselage in the HF band may even exceed the external field, due to constructive interference of reflected waves within the fuselage. These strong electromagnetic fields can potentially affect the aircraft electronics directly.
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