Sonar unit

1. A sonar unit comprising:

a transducer configured to receive an ultrasonic wave;

a rectangular circuit substrate on which the transducer, electronic components constituting a circuit configured to drive the transducer, and an input-output terminal for the circuit are mounted, the transducer comprising a body housing a piezoelectric element on a first side of the rectangular circuit substrate; and

a shield unit placed in the rectangular circuit substrate, the shield unit being configured to block an electromagnetic wave incident on the electronic components, wherein:

the input-output terminal is placed on a first end side of the rectangular circuit substrate in a longitudinal direction of the rectangular circuit substrate;

the shield unit includes a plate portion at a position where the plate portion overlaps at least a part of the electronic components when the shield unit is viewed in a thickness direction of the rectangular circuit substrate, the plate portion of the shield unit being on a second side of the rectangular circuit substrate opposite the first side;

the shield unit includes a window portion provided as a through-hole or a notch penetrating through the plate portion in a thickness direction of the plate portion; and

the window portion is placed at a position close to the input-output terminal in the longitudinal direction of the rectangular circuit substrate, without overlapping the input-output terminal, when the window portion is viewed in the thickness direction of the rectangular circuit substrate.

2. The sonar unit according to claim 1 , wherein:

the input-output terminal includes a GND terminal connected to ground;

the rectangular circuit substrate is electrically connected to the GND terminal and has a first through-hole having the same potential as the GND terminal;

the shield unit includes an attachment terminal to be attached to the rectangular circuit substrate and is electrically connected to the first through-hole and joined to the first through-hole in a state where the attachment terminal is passed through the first through-hole; and

the first through-hole is disposed at a position where a distance to the GND terminal is shortest among terminals included in the input-output terminal.

3. The sonar unit according to claim 1 , further comprising a housing in which the transducer and the shield unit are accommodated in a state where the transducer and the shield unit are mounted on the rectangular circuit substrate, wherein the rectangular circuit substrate has a communicating passage through which a space on a first surface side of the rectangular circuit substrate communicates with a space on a second surface side of the rectangular circuit substrate.

4. The sonar unit according to claim 1 , wherein a distance between the plate portion and the rectangular circuit substrate becomes shorter from the first end side toward a second end side of the rectangular circuit substrate in the longitudinal direction.

5. The sonar unit according to claim 1 , wherein:

the rectangular circuit substrate includes second through-holes through which lead terminals of the transducer are passed in an electrically connected manner; and

the transducer and the second through-holes overlap the window portion when the transducer and the second through-holes are viewed in the thickness direction of the rectangular circuit substrate.