Originally Posted by E:V:A
If that is the case, you're probably doing something right!
The cover itself changes the properties of the antenna, usually they compensate this with a velocity factor. What happens, is that the antenna seem larger than it should be, when the cover is closed. Try to compensate by reducing your micro-strip dimensions by multiplying them with ~0.97. Microstrip and patch antennas have a very narrow band-width... (You'll have to be accurate to the mm.) Also make sure the antenna is not touching anything inside, when the cover is closed, as that would again change the properties.
I have three, two are active devices, with the receiver attached beneath, and require +3 VDC supply and RS-232 for data.
One is a ceramic patch from O.E.M Garmin, as supplied in their hand held units,
The third, is a patch used by old Garmin Flight navigator unit I used in my B-55 Baron. Its dimensions are 2-3/8" on a side, soI doubt you could fit this inside without difficulty, let alone altering the dielectric constant of the board.
But if you have a sizable space between the cover and the main board, you may be able to fit a small ceramic patch antenna that should work nicely, IF the feed impedances are similar.
he enclosed pics should give you a starting point though..