Dispersion analysis of the shielded sievenpiper structure using multiconductor transmission-line theory

Dispersion curves for the shielded Sievenpiper "mushroom" structure are obtained by means of multiconductor transmission-line (MTL) theory. This inherently quasitransverse electromagnetic mode (quasi-TEM) analysis is used to quickly and accurately calculate the dispersion of the lowest pass-band and several of the upper pass-bands. The first pass-band reveals dual mode behavior, supporting one forward-wave and one backward-wave mode, with the first stop-band formed as a result of contra-directional coupling between the two modes. The dispersion curves obtained using MTL theory are compared with full-wave simulations, with excellent agreement between the two methods. Moreover, the analysis reveals an interesting modal behavior within the stop-band, corresponding to complex conjugate propagation constants. The overall modal structure within the various bands is examined and related to corresponding applications.