In recent years, the Helix properties are analized by solving Maxwell's equation, but the determination of the terminal condition is very complicated. Usually we use the Helix combined with other microwave circuits, such as wave-guides or coaxial cables. So, it is important that terminal impedance should be defined.
The helix has a continuous and a periodical properties. In this paper, two approximation methods are discussed. One is the distributed-line method, of which equivalent circuit has a continuous property, but not periodical. The other is the lumped-circuit method, of which equivalent circuit has the contrary property to the distributed-line.
The Helix properties would not be perfectly represented by both methods but characteristic impedance, propagation constant and terminal condition can be easily determined by these approximation methods.