US Patent 6992636 Dielectric substrate with selectively controlled effective permittivity and loss tangent

A substrate (300) for an RF device includes a plurality of layers (102) of dielectric material cofired in a stack. The plurality of layers (102) is formed from a material having a permittivity. Selected ones of the layers (102) have a pattern of perforations (106) formed in at least one perforated area (104). The perforated areas (104) are generally aligned with one another in the stack to lower one or more of an effective value of a permittivity and a loss tangent in a least one spatially defined region (504) of the substrate (300).