The self-resonance insertion loss dip of a feedthrough capacitor is reduced or eliminated by raising the equivalent series resistance of the capacitor, thus minimizing the capacitor Q. The equivalent series resistance of the capacitor can be raised by forming voids in the active and/or ground electrode plates of the capacitor. The electrode plates may be formed so as to have a relatively reduced thickness, or a relatively increased thickness. A conductive material having a relatively high resistivity may be used to form the active and/or ground electrode plates of the capacitor. Alternatively, the conductive material forming the electrode plates may have a dielectric material added thereto.