Methods and apparatus for a low k dielectric layer of porous SiCOH. The first lens L1 has a positive power and a meniscus shape with a convex surface facing an object; and the second lens L2 has a positive power with a convex surface facing an image. At least one metering section is selectively controllable to not meter product while at least one other metering section is metering product. The switching element is adapted to selectively complete and break an electrical circuit between the first and second connection means in response to a control signal supplied thereto. The surveillance system also comprises a second mounting interface configured for coupling a second antenna to the aircraft.