Ray analysis of electromagnetic field build-up and quality factor of electrically large shielded enclosures

A high-frequency asymptotic ray solution is investigated for predicting the electromagnetic field build up and steady-state parameters of shielded enclosures or cavities, which are large with respect to wavelength. It is found that the ray solution can deterministically predict the early-time field build up after the source is switched on, but cannot predict the steady-state fields of high-Q enclosures because of the intractably large number of ray reflections required for convergence. However, it is demonstrated that the steady-state Q factor may be predicted from the early-time energy density build up at a point by coherently summing the power in each ray. The Q factor is obtained via its relationship to the cavity time constant, which may be extracted from the early time energy density curve. A clear indication of polarization diversity throughout the enclosure may also be obtained by plotting the polarization components of the early-time fields and energy density build up at different points. The advantage of the ray method is that it can be used to treat large closed cavities of relatively arbitrary shape.