Giant gaps in photonic band structures

We have investigated electromagnetic transmission through a one-dimensional waveguide along which stars of N^' side branches were grafted at N equidistant sites, N and N^' being integers. Analytic expressions are reported for the corresponding band structure for large N and for the transmission coefficient for any value of N and N^'. Numerical results exhibit the existence of periodic very narrow photonic bands separated by large gaps, for N and N^'~5 to 10. The above generic and universal behaviors of these waveguides were confirmed by experiments using coaxial cables.