What kind of transmission line is made of two conductors held apart by insulated rods?

Open-wire transmission line consists of two parallel wires separated primarily by air. To maintain a constant distance between the conductors without fully encasing them in plastic, small insulated rods or spacers are placed at regular intervals along the line. Because air is an excellent dielectric, open-wire line has very low signal loss compared to lines using solid insulation. It is easily distinguished from window line, which embeds the wires in continuous or semi-continuous plastic, and coaxial cable, which relies on a concentric inner and outer conductor design.