Introduction to RF Radiation Safety / 4 / 4.2 / 4.2.3

4.2.3 Propagation Modes Related To Frequency Band

In most RF transmissions, multiple propagation mechanisms are present, although one typically dominates depending on frequency and geometry, as illustrated in Figure 4.7. In general:

• Surface-wave propagation is most effective at low frequencies (LF and MF bands).
• Sky-wave propagation dominates the HF band (3–30 MHz) where ionospheric refraction is strong.
• Space-wave and troposcatter modes become predominant at VHF, UHF, and microwave frequencies, where line-of-sight and atmospheric effects govern link design.