A SHIELDED PAIR has parallel conductors separated by a solid dielectric and surrounded by
copper braided tubing. The conductors are balanced to ground.
RIGID COAXIAL LINE contains two concentric conductors insulated from each other by spacers.
Some rigid coaxial lines are pressurized with an inert gas to prevent moisture from entering.
High-frequency losses are less than with other lines.
FLEXIBLE COAXIAL LINES consist of a flexible inner conductor and a concentric outer
conductor of metal braid. The two are separated by a continuous insulating material.
WAVEGUIDES are hollow metal tubes used to transfer energy from one point to another. The
energy travels slower in a waveguide than in free space.