A first mark is provided on a rotatable member, or on a connector on which the rotatable member is rotatably mounted. The generally C-shaped section comprises a flattened portion near the first, flattened section, and a curved portion extending to a free edge. The proposed network may operate correctly regardless of the delay in the interconnecting wires. The second lens is a positive lens having a convex surface having a large curvature at an image side. Input signals are mixed with signals from the power splitter by the first mixer, and the lower frequency component of the output signals from the first mixer is removed by a second bandpass filter and is passed to the third mixer. The actuator is clamped between two metallic plates, each arranged against a face.