ANTENNA BRANCHING FILTER

摘要

PROBLEM TO BE SOLVED: To secure a phase matching function of a phase shifter, and to improve an attenuation characteristic in an optional band in an out-of-pass band of high-band side and low-band side filters. SOLUTION: In an antenna branching filter including a high-band side filter 11, a low-band side filter 12, and a phase shifter 14 in a low pass configuration inserted between the high-band side filter and an antenna port and taking the phase matching of both filters, a resonance inductor 18 resonating with a capacitor 17 on the antenna port side is provided to obtain an attenuation characteristic in an optional band in an out-of-pass band of both filters by the resonance. For instance, maximum attenuation is held at twice of a center frequency fLof a pass band of the low-band side filter. The LC resonance circuit configuration can be desirably modified into such a configuration that a resonance capacitor is provided in series to an inductor in a phase shifter having a high-band side filter configuration. COPYRIGHT: (C)2009,JPO&INPIT