Electromagnetic field predictions inside screened enclosures containing radiators

In order to understand how a PCB inside an enclosure with apertures radiates externally, it is first necessary to understand how the PCB excites the environment internal to the enclosure. This paper describes a simple method which can be used to predict the electric and magnetic fields within a screened enclosure, treating the PCB as a combination of electric and magnetic dipoles with internal impedances. The enclosure is treated as a superposition of transmission lines (one for each waveguide mode) which are short circuited at each end. Mode coupling is taken into account in both the magnetic and electric cases. The method is used to predict the coupling between two loops which are introduced into the enclosure, and also between two electric monopoles which are introduced into the enclosure. Good agreement with experiment is found below 600 MHz (approximately twice the lowest cut off frequency), by considering only the TE10 waveguide mode. Agreement at higher frequencies is qualitatively good, and is improved further by taking into account one or two higher order modes