Band rejection filter for e.g. digital video broadcasting - handheld TV receiver, has secondary signal transmission channel comprising resonant element and negative resistance circuit that reduces insertion loss of filter

摘要

The filter (20) has a direct signal transmission channel (23) and a secondary signal transmission channel (24) arranged between a filter input (21) and a filter output (22), where the filter is formed on an FR4 substrate. The secondary channel has a resonant element whose resonant frequency is equal to a rejection frequency. The channels introduce, at the rejection frequency, a phase difference of 180 degrees between signals circulating through the direct and secondary channels. The secondary channel has a negative resistance circuit (246) to reduce insertion loss of the filter.