Adjustable dual-mode band-pass filter with high selectivity and constant bandwidth

The invention discloses an adjustable dual-mode band-pass filter with high selectivity and constant bandwidth. The filter comprises a dielectric substrate, and two horizontal feeder lines, a dual-moderesonator and two varactors, which are printed on the dielectric substrate; the two horizontal feeder lines are parallel to each other; the dual-mode resonator comprises two coupling parts, two folding parts, a vertical part and a short section line; the two coupling parts are parallel to each other and symmetrically arranged on the outer sides of the two horizontal feeder lines; the coupling parts are connected with the folding parts; the tail ends of the folding parts are connected with the vertical part through the varactors; the short section line is overlapped with a horizontal shaft; the short section line is connected with the vertical part; and a metal through hole is formed in the tail end of the short section line. The filter has three zero points which are positioned on the twosides of a passband and a