Band pass filter, antenna duplexer, and communication apparatus

摘要

There is provided a band pass filter comprising three or more resonant-line holes (2a, 2b, 2c) disposed in a dielectric block (1), a resonant line (5a, 5b, 5c) formed on each inner surface of the holes, and an outer conductor (3) disposed on the outer surfaces of the dielectric block (1) so that a dielectric filter is formed; wherein one end of the resonant line (5a - 5c) is a short-circuited end, and the other end thereof is an open end; the sectional area size of each of the resonant-line holes (2a - 2c) is changed at a certain point in the axial direction of the resonant-line hole (2a - 2c); the sectional area size on the short-circuited-end side or open-end side of at least one (2b) of the plurality of resonant-line holes (2a - 2c) is made differently from those of the other resonant-line holes (2a - 2c); and regarding the resonant-line holes (2a - 2c) symmetric with respect to a symmetry axis made at the center in a direction in which the plurality of resonant-line holes (2a - 2c) is aligned, the sectional area sizes of the shod-circuited-end side or open-end side thereof are made the same so as to form coupling between adjacent resonant lines. <IMAGE>