The Funnel Trap works just how you would imagine and while it means there is only on entrance, it also has the advantage of only one exit so is harder to find.
The funnel is mounted in the centre of a flat cage top with mesh covering all the rest of the surface.

This is a ‘funnel’ for a Funnel Trap

This close up of the ‘funnel’ shows how the mesh sides are held together with cable ties.