How does parallel conductor transmission line compare to coaxial cable with a plastic dielectric?

Parallel conductor transmission lines, such as open-wire or ladder line, primarily use air as their dielectric material. Because air absorbs virtually no RF energy, these lines suffer from exceptionally low dielectric losses compared to standard coaxial cables. Coaxial cables rely on solid or foam plastic dielectrics to separate the center conductor from the outer shield. This plastic material introduces dielectric heating when exposed to RF, which inherently increases signal attenuation (loss). The other options are incorrect because SWR and reflection coefficients depend on how well the transmission line matches the load antenna, not on the type of line itself. Additionally, air-insulated parallel lines have a higher, not lower, velocity factor than plastic dielectric coax.