Abstract: A composite microwave circuit module assembly has a dielectric substrate which is formed by a lower layer, an intermediate layer and an upper layer. The lower layer and the upper layer include a lower ground surface and an upper ground surface, respectively, and the intermediate layer includes a radio frequency signal circuit formed by an active circuit element and a passive circuit element. A number of via-holes filled with metal are arranged along the radio frequency signal circuit to short-circuit the upper ground surface and the lower ground surface so as to shield the radio frequency signal circuit. An element mounting cavity is disposed on the intermediate layer with a portion of dielectric above the intermediate layer being removed, and the active circuit element is mounted on an element mounting land in the cavity. The cavity is covered by a conductor plate member.