| 摘要 |
Here disclosed is a parallel-resonance type band-pass filter, which is employed for mobile communications equipment such as a mobile phone. According to the filter, each resonator has a single capacitor and serially connected plural inductors both of which are formed on the surface or on an inner layer of a substrate. Electromagnetic coupling between the resonators is established through electromagnetic coupling between at least a pair of inductors-the inductors of the pair belong to respective resonators. The input and the output terminals are coupled with the respective resonators via the capacitor having a properly determined capacitance. With such a simple structure, the filter also can work as an impedance transformer, with the result that the mobile communications equipment will be much smaller.
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