Multidielectric microstrip filter

Abstract

A multidielectric electrical filter is adapted for passing a primary electrical signal at a first frequency while attenuating higher frequency signals, most notably harmonic spurs. The filter comprises an elongated transmission line and one or more radial pads overlying a first surface of a dielectric support opposite a ground plate. The support is formed of a first dielectric material to achieve a desired capacitive coupling between the pad and the ground plate effective to attenuate the higher frequency signals. The support further comprises a region underlying the transmission line and containing a second dielectric material having a dielectric constant distinct from the first material. Preferably, the region includes one or more slots containing air to minimize the capacitive coupling between the transmisison line and the ground plate and thereby reduce insertion loss of the primary signal that would otherwise lessen the power of the signal to the antenna.