portions of an upper end face of the dielectric ceramic block 2 at which upper ends of the resonators 3 a 3 c 4 a 4 b and 6 open i e at which these ends terminate serve as open circuit ends 8 a where the external conductor 7 is absent portions of a lower end face of the dielectric ceramic block 2 at which lower ends of the resonators 3 a 3 c 4 a 4 b and 6 open or terminate serve as short circuit ends 9 a where the external conductor 7 is present see fig3 the antenna excitation hole 15 a and the transmission excitation hole 15 b formed between the resonators 3 a 3 c 4 a 4 b and 6 are of an interdigital structure in relation to the resonators 3 a 3 c 4 a 4 b and 6 specifically short circuit ends 9 b for the excitation holes 15 a and 15 b are formed on the upper end face of the dielectric ceramic block 2 where the open ends 8 a for the resonators 3 a 3 c 4 a 4 b and 6 are provided whereas open ends 8 b for the excitation holes 15 a and 15 b are formed on the lower end face of the dielectric ceramic block 2 where the short circuit ends 9 a for the resonators 3 a 3 c 4 a 4 b and 6 are provided as shown in fig1 and 2 in the open ends 8 a a circular recess 10 is formed at the upper end of each of the through holes 5 which constitute the resonators 3 a 3 c 4 a 4 b and 6.