Slow wave propagation

Slow waves can propagate when the waveguide has periodic boundaries. The properties of slow waves can be derived by a formal mathematical treatment of wave solutions in a periodic structure [6]. These periodic structures are annular metal pieces called irises, attached to the outer conductor. The irises have inner radius $R$ and spacing $\delta$ . The magnetic fields are almost identical to those of the standard transmission line except for field exclusion from the irises; this effect is small if the irises are thin. In contrast, radial electric fields cannot penetrate into the region between irises. Electric fields are restricted to the region between the inner conductor and inner radius of the irises. The result is that the inductance per unit length is almost unchanged, but C is significantly increased.