A filtering unit, comprising: a) two coupled coplanar waveguide CPW slow-wave resonance units, wherein each slow-wave resonance unit comprises: a substrate, a CPW transmission line and a tapered CPW transmission line that are disposed on the substrate, wherein the CPW transmission line and the tapered CPW transmission line of each slow-wave resonance unit are arranged next to each other and the tapered CPW transmission lines of both slow-wave resonance units are facing each other; wherein b) each CPW transmission line comprises a first central signal line, a first ground plane arranged on each of two sides of the first central signal line and a first insulation slot with an invariable width g2 disposed between the first central signal line and the first ground plane, the first central signal line of the CPW transmission line having an invariable width W1 and a length L1, and widths g2 of the first insulation slot on two sides of the first central signal line remain unchanged; c) each tapered CPW transmission line comprises a second central signal line connected to the first central signal line, a second ground plane arranged on each of two sides of the second central signal line and a second insulation slot with a tapered width disposed between the second central signal line and the second ground plane, the second central signal line of the tapered CPW transmission line having an invariable width W2 and a length L2, and widths of the second insulation slot on two sides of the second central signal line gradually decrease in both tapered CPW transmission lines or gradually increase in both tapered CPW transmission lines in the facing direction of the two tapered CPW transmission lines; and d) a ground stub shared by both resonance units and disposed in a connection plane between both resonance units and connecting both second central signal lines with both second ground planes at both sides of the second central signal lines, wherein one end of the ground stub which is far away from the second central signal line is connected to the second ground plane; and e) wherein W1>W2. a) two coupled coplanar waveguide CPW slow-wave resonance units, wherein each slow-wave resonance unit comprises: a substrate, a CPW transmission line and a tapered CPW transmission line that are disposed on the substrate, wherein the CPW transmission line and the tapered CPW transmission line of each slow-wave resonance unit are arranged next to each other and the tapered CPW transmission lines of both slow-wave resonance units are facing each other; wherein b) each CPW transmission line comprises a first central signal line, a first ground plane arranged on each of two sides of the first central signal line and a first insulation slot with an invariable width g2 disposed between the first central signal line and the first ground plane, the first central signal line of the CPW transmission line having an invariable width W1 and a length L1, and widths g2 of the first insulation slot on two sides of the first central signal line remain unchanged; c) each tapered CPW transmission line comprises a second central signal line connected to the first central signal line, a second ground plane arranged on each of two sides of the second central signal line and a second insulation slot with a tapered width disposed between the second central signal line and the second ground plane, the second central signal line of the tapered CPW transmission line having an invariable width W2 and a length L2, and widths of the second insulation slot on two sides of the second central signal line gradually decrease in both tapered CPW transmission lines or gradually increase in both tapered CPW transmission lines in the facing direction of the two tapered CPW transmission lines; and d) a ground stub shared by both resonance units and disposed in a connection plane between both resonance units and connecting both second central signal lines with both second ground planes at both sides of the second central signal lines, wherein one end of the ground stub which is far away from the second central signal line is connected to the second ground plane; and e) wherein W1>W2.