Let's consider a perfect cubic Faraday-cage with solid metal walls of several centimeters' thickness. Radio waves from the microwave region are fully blocked by this cage, and the fieldstrength inside this cage is zero.
What happens when six narrow slits (with a length of multiple wavelengths, and a width multiple times lower than a wavelength) are made in all the six walls of the cube? Is there anything left of the initial shielding inside? And more important: do these slits become sources of radiation themselves, as the two url's below suggest? And will the emitted wave patterns interfere with each other, forming nodes and anti-nodes inside the cage? Moreover: can this result in area's inside the cage with an even higher intensity than that of the incoming field? And finally: is positioning of the slits possible in such a way that their emitted waves cancel each other out?
These two url's suggest that slits or holes in a Faraday-cage will form new sources of radio-waves that will radiate inside the Faraday-cage: