I managed to get the "radar" screen displayed.
The problem was ArduCopter 3.4.6. When I switched to 3.5-rc11, a window simply poped-up.
I don't recall now why I thought 3.4 was enough. Maybe a mistake.
Although MP displays the screen, its bahavior is quite weird. Radar window is initially displayed with a white background. Then, it switches to dark grey. Then multiple windows are displayed, with the same content. After about 1 minute, a error window is displayed, while all radar windows display a red "X" on white background. The error message varies. If I disconnect and then reconnect to ArduCopter, lots of radar windows are displayed instantly, and I have to close them all.
I'm still trying to understand what is happening.