An apparatus having a package, a wall and a lid is disclosed. The package may be configured to mount a plurality of chips. Two of the chips may generate a plurality of signals in a millimeter-wave frequency range. A metal is exposed at a surface of the package between the two chips. The metal is generally connected to an electrical ground. The wall may be formed on the metal and between the two chips. The wall generally has a plurality of arches that (i) are conductive, (ii) are wire bonded to the metal and (iii) attenuate an electromagnetic coupling between the two chips at the millimeter-wave frequency. The lid may be configured to enclose the chips to form a millimeter-wave cavity.