An infinite transmission line or waveguide periodically loaded with reactive elements is
an example of a periodic structure. As shown in Figure 8.1, periodic structures can take
various forms, depending on the transmission line media being used. Often the loading
elements are formed as discontinuities in the line itself, but in any case they can be modeled
as lumped reactances in shunt (or series) on a transmission line, as shown in Figure 8.2.
Periodic structures support slow-wave propagation (slower than the phase velocity of the