holes on a metal package of a microwave circuit

Hi all,

I've got a microwave receiver with a local oscillator cct. running at 11GHz packaged inside a metal housing.

Can I have few holes on the housing which does not allow leakage of 11 GHz signal outside from the housing?

What's the maximum size of the hole which does not allow RF out @11 GHz?

cheers,
per_lube

I made holes in metal housing for additional wires without sensible degradation in receiving circuit performance. Maybe it would be good idea to make it away from LO oscillating part, and put some absorbing material in the hole.