resonator 30 is an example of an ideal model of the present invention for estimation calculation omitting the influence of an input output terminal which forms a 1 2 wave length resonator according to the inventors 39 estimation there does not result as much calculation errors between the ideal model disclosed in fig2 and this embodiment an actual example of the 1 2 wave length resonator having such the input output terminal 34c is illustrated in fig3 b in fig3 b the same reference numerals denote the same or equivalent elements as illustrated in fig3 a in fig3 b a part of the second grounding layer 34 on the front surface of the dielectric plate 42 is separated into two guide portions 34a and 34b for guiding the input output terminal 34c to define slits 35a and 35b the input output terminal 34c is provided by a plating on the front surface and is connected to an outer circuit 34d partially omitted which applies an input signal to the resonator 44 and also receives an output signal from the resonator 44 further the input output terminal 34c is connected to one end of a microstrip line 36 39 at an edge of the top surface of the dielectric plate 42 as mentioned above even though the entire bottom surface of the dielectric plate 42 is covered by a first grounding layer 38 the input output terminal 34c and the outer circuit 34d are electrically separated from the first grounding layer 38 by a small slot not shown located on a reverse side of a connecting point between the input output terminal 34c and the outer circuit 34d on the front surface which is adjacent to an edge of the bottom surface to prevent a short circuit since the first and.