A high frequency module for amplifying a microwave signal is used for communication equipment for communication in a microwave band, radar equipment, a power transmission device, and the like. The high frequency module includes high frequency integrated circuits such as an FET (Field Effect Transistor) and an MMIC (Monolithic Microwave Integrated Circuit). Since a high frequency integrated circuit generates heat with its power consumption or the like, the high frequency module includes a heat dissipation sink and the like for cooling the high frequency integrated circuit. However, in the case where a mounting area is limited, the case where an antenna element is formed on the back surface of the dielectric multilayer substrate on which a high frequency integrated circuit is mounted, and the like, it is not possible to provide means for dissipating heat from the bonding surface of the high frequency integrated circuit directly to the heat dissipation sink, so that it becomes necessary to provide another cooling means.
For example, Japanese Patent Laying-Open No. 09-102579 (see PTD 1) discloses a high frequency module configured to have an external casing formed of an exterior metal cover, in which the side surface of an interior metal cover is internally in contact with the inside of this exterior metal cover. The high frequency module disclosed in PTD 1 includes, on the inside of the exterior metal cover, a dielectric substrate, a high frequency integrated circuit and a window. The dielectric multilayer substrate is housed inside the interior metal cover. The high frequency integrated circuit is mounted on the outside of the interior metal cover. The window is provided so as to penetrate through the interior metal cover and provided as an opening through which a wiring line passes, the wiring line being used for connecting the high frequency integrated circuit to the dielectric multilayer substrate.