The key points of this chapter:
- EM waves are coupled electric and magnetic fields; they need no medium and travel at the speed of light.
- A wave is described by frequency/wavelength (c = f × λ), amplitude, phase and polarisation.
- Waves in phase reinforce each other, waves in antiphase cancel each other out — the basis of phased arrays, multipath effects and coherent signal processing.
- The EMS runs from radio waves to gamma radiation; low frequencies reach far but are coarse, high frequencies are precise but weather-sensitive.
- AM varies the amplitude of the carrier, FM the frequency; modulation is both the carrier of information and a recognition feature for EW.
In the next chapter we link the regions of the EMS to their concrete military applications.