An improved RF/microwave stripline structure fabricated from a PWB suspended inside of a sheet metal enclosure. The enclosure is formed by top and bottom sheet metal covers each having a plurality of flanges that are coupled to the PWB. The PWB contains identical conductive transmission lines on its top and bottom layers. Plated through holes electrically couple the transmission lines on both layers of the PWB. RF/microwave input and output connectors extend through the bottom cover and are coupled to the transmission lines. Critical dimensions between the transmission lines are controlled by the PWB artwork and are not effected by any misalignment of mechanical parts.