A filtering unit includes a housing having outer walls that define a volume and an inner wall that separates the volume into a first chamber and a second chamber. The filtering unit also includes a rigid/flexible circuit board. The circuit board includes a first rigid portion designed to be positioned in the first chamber. The circuit board further includes a second rigid portion designed to be positioned in the second chamber. The circuit board further includes a flexible portion connecting the first rigid portion to the second rigid portion and designed to extend around the inner wall from the first chamber to the second chamber. The filtering unit further includes a bumper designed to be positioned between one of the outer walls and the inner wall to provide waveguide functionality by reducing an amount of electric field that can pass from the first chamber to the second chamber.