Abstract: RF feedthroughs for use with monolithic microwave integrated circuits (MMIC) are installed in environmentally protective or hermetically sealed packages that provide electromagnetic shielding. A feedthrough for an MMIC package has a dielectric substrate, a microstrip or transmission line formed on the substrate for transmitting high frequency electronic signals and a wall disposed above the transmission line and the substrate. The wall of the feedthrough has a varying thickness so that the narrowest portion of the wall is disposed on the transmission line substantially perpendicular to the substrate. The transmission line also has a varying width so that the narrowest width portion of the transmission line crosses the narrowest portion of the wall. The narrowest portion of the wall may be created by placing two oppositely facing concaved surfaces on each side of the wall. To reduce parasitic capacitance, the substrate and the wall may each have an air cavity embedded in respective bodies.

Abstract: A hermetically sealed package assembly for microwave circuits in the high microwave frequencies having a dielectric gap defined in the substrate. The package assembly comprises a substrate for carrying the circuit on a top surface, a seal ring wall carried on the top surface, a via structure provided through the substrate for transmitting high-frequency signals into and out of the package, and a conducive lead carried on the bottom surface of the substrate and passes under the seal ring wall. A dielectric gap is provided in the substrate between the seal ring wall and the lead to reduce the capacitive coupling between the lead and the wall. The gap may be a sealed cavity provided inside the substrate, or a cutout area in the substrate so that the lead is suspended in air at the location where it passes under the seal ring wall.