Wideband filters employing multilayer gratings

Multilayer surfaces, consisting of stacked inductive and capacitive strips or grids, have been used to design wideband filters in the 5-40 GHz range, with rapid transitions between reflection and transmission. For singly polarised applications, transmission bandwidths of 70-100% and edge transition ratios of 1.1-1.3 are realisable at 45° TM incidence using 4-8 layers of capacitive and inductive strips. Factors which constrain the passbands are highlighted. In dual polarised designs using doubly periodic grids, the widths are restricted to 35-40% by TE incidence grating responses at the upper passband edge. In TM they are even more restricted by a TE₁₁ mode resonance. Wider passbands require high inductances to reduce the low frequency edge, implying very fine conductors