Acoustic wave filter

1. An acoustic wave filter, comprising:

(a) an input-side IDT electrode and an output-side IDT electrode arranged on a piezoelectric substrate along an acoustic wave propagation direction and separated from each other,

(b) the input-side IDT electrode includes a ground port and an input port serves as an input signal port, and the output-side IDT electrode includes a ground port and an output port serves as an output signal port;

(c) at least one of the input-side IDT electrode and the output-side IDT electrode is configured such that:

(c1) electrode fingers extends from each of a pair of bus bars arranged in parallel with each other to extend along an acoustic wave propagation direction to an opposite bus bar side, so that a plurality of IDT blocks in which a group of electrode fingers are arranged in a comb-tooth shape are arranged side by side along the acoustic wave propagation direction and are connected in series through each of the bus bars;

(c2) among the bus bars located in both ends of a group of the IDT blocks connected to each other in series, the bus bar facing an area between the input-side IDT electrode and the output-side IDT electrode is connected to the ground port, and the bus bar located in an opposite side of the area is connected to one of the signal ports;

(c3) a group of the electrode fingers of each IDT block is configured such that a period unit is cyclically repeated along the acoustic wave propagation direction, said period unit being an overall dimension of three neighboring electrode ringers extending from one of the bus bars and a single electrode finger neighboring to the three electrode fingers and extending from the other bus bar out of the pair of the bus bars of each IDT block,

(c4) an interval between the neighboring IDT blocks is set such that the period unit is cyclically repeated in the IDT electrode;

(c5) a space area is formed between the neighboring IDT blocks, and the space area is corresponding to one or more electrode fingers arranged side by side of the electrode fingers arranged side by side; and

(c6) among the neighboring IDT blocks, the electrode finger disposed at an end portion is extended from the bus bar which connects the neighboring IDT blocks in series, and the end portion is located next to the space area on the IDT block that is closer to the connected signal port.

2. The acoustic wave filter according to claim 1 , wherein

the interval between the neighboring IDT blocks is set to a dimension equal to or more than λa/4, wherein a dimension corresponding to the period unit is set as λa.

3. The acoustic wave filter according to claim 1 , wherein

the interval between the neighboring IDT blocks is set to a value, which is (λa/4)×n×α, wherein n is natural number equal to or more than 1, and α is 1.0005 to 1.07.

4. The acoustic wave filter according to claim 1 , wherein,

in the group of the period unit cyclically repeated along the acoustic wave propagation direction, the period unit includes:

three neighboring electrode fingers extending from one of the bus bars; and

a single electrode finger neighboring to the three electrode fingers and extending from the other bus bar out of the pair of bus bars.

5. The acoustic wave filter according to claim 1 , wherein,

in the group of the period unit cyclically repeated along the acoustic wave propagation direction, the period unit includes:

a single electrode finger and a reflection electrode, disposed in neighboring and extending from one of the bus bars; and

a single electrode finger, neighboring to a set of the single electrode finger and the reflection electrode and extending from the other bus bar out of the pair of bus bars.

6. The acoustic wave filter according to claim 1 , wherein,

in the group of the period unit cyclically repeated along the acoustic wave propagation direction, the period unit includes:

four neighboring electrode fingers extending from one of the bus bars.