A filtering unit (60). The filtering unit (60) comprises: two slow-wave resonance units (3) that are mutually coupled, and each slow-wave resonance unit (3) consists of a CPW transmission wire (10), agradually-changing CPW transmission wire (20) and a grounding branch (40). A slow-wave feature can b generated, a higher harmonic of a baseband signal can be driven to a high-frequency, so as to implement a wide stopband feature. In addition, by using a slow-wave effect, the size of a filter can be properly designed and accordingly the whole area of the filter can be reduced, and costs can be reduced; the coupling of the two slow-wave resonance units (3) can improve passband performance of the filter, the bandwidth can be increased, the flatness in a passband can be increased, and insertion loss can be reduced.