Piezoelectric filter, antenna duplexer, and communications apparatus employing piezoelectric resonator

1. A piezoelectric filter comprising:

a substrate; and

a plurality of piezoelectric resonators provided on the same said substrate, wherein said plurality of piezoelectric resonators each comprises:

a cavity formed in said substrate;

a lower electrode formed on said substrate, covering said cavity;

a piezoelectric material layer formed on said lower electrode; and

an upper electrode formed on said piezoelectric material layer, and

at least one of said plurality of piezoelectric resonators has a cavity formed of two semilunar cells that have the same shape obtained by dividing a circle into two and are arranged axisymmetrically.

2. The piezoelectric filter according to claim 1 , wherein said at least one of the plurality of piezoelectric resonators having the cavity formed of the two semilunar cells has a lower impedance than that of another piezoelectric resonator.

3. The piezoelectric filter according to claim 1 , wherein each said cavity penetrates through said substrate.

4. The piezoelectric filter according to claim 3 , wherein the two semilunar cells are connected to each other in a surface closer to the lower electrode.

5. An antenna duplexer, wherein the piezoelectric filter according to claim 1 is employed as at least one of a transmission filter and a reception filter.

6. A communications apparatus comprising:

an antenna;

a transmission device;

a reception device; and

the antenna duplexer according to claim 5 provided between said antenna, and said transmission device and said reception device.