What kind of transmission line has two wires side-by-side embedded in insulating material?

A transmission line that consists of two parallel wires embedded in a ribbon of insulating material is known as twin-lead or window line. The term 'window line' specifically refers to a type of parallel-conductor line where rectangular 'windows' are cut out of the insulating plastic to reduce dielectric loss while maintaining consistent wire spacing. Other options are incorrect because they describe fundamentally different physical structures. Coaxial cable consists of a single center conductor surrounded by a tubular braided shield. An open-wire line uses intermittent insulating rods rather than embedding the wires, and a waveguide is a hollow metal tube used primarily for microwave frequencies.