Use of Mutual Coupling to Decrease Parasitic Inductance of Shunt Capacitor Filters

In this paper, we propose and study several new designs of a shunt capacitor filter with two surface-mount technology capacitors. These designs make use of mutual inductance effects to increase the attenuation provided by the filter in the range of high frequencies where the filter behaves inductively. We provide lumped element circuit models for the proposed designs that allow identification of the key inductive parameters that determine the high-frequency performance of these filters. We obtain the equations relating these parameters to the effective inductance of the filter, which can be used to compare the high-frequency behavior of different filter designs. We have fabricated and measured several compact shunt capacitor filters with improved performance at high frequencies. We have found that, compared with a shunt capacitor filter with one capacitor, a proper filter design with two capacitors can easily increase in 15-20 dB the high-frequency attenuation provided by the filter. This design also outperforms by 10-15 dB a traditional shunt capacitor filter with two capacitors closely placed. Moreover, this improvement is obtained with no increase in size, cost, or time of design of the filter.