In a slightly dated article (2018), Russian scientists report on numerically simulating the EM properties (resonance and energy concentration) of the Great Pyramid using radio frequencies (wavelengths between 200-600 m). Major take-a-ways: (1) the Pyramid’s chambers concentrate EM energy at resonant conditions (Figs. 2 and 3), (2) the Pyramid also scatters EM waves and focuses them into the substrate below it (Fig. 6), and (3) in general, pyramidal objects can significantly suppress the reflection of incident EM waves, which can be used to control radio-wave propagation and reflection.
Looks like subterranean chambers may be just as important as above ground chambers…