An antenna assembly is formed from at least one antenna and associated conductive connecting element mounted within a deformable membrane that allows the antenna assembly to be installed or fixed within a narrow gap or crevice, wherein the gap or crevice may be subject to harsh environmental conditions. The apparatus includes an external light source, a low magnification image-forming optical system, an electrical control system and a monitor. A guide element on the wall that guides the valve plate over the end section of the closing path interacts with a guide element on the valve plate.