Comparison of bandwidths of mushroom-type electromagnetic bandgap surfaces and corrugated and strip-type soft surfaces when used as narrow ground planes

The authors compare different types of corrugated and strip-loaded soft surfaces and mushroom-type electromagnetic bandgap (EBG) surfaces in terms of the bandwidth of a system-related performance parameter, when they are used as narrow ground planes to reduce back radiation. To this aim an incremental electrical source on an infinitely long ground plane of finite width is analysed. The strip-loaded soft surfaces are improved with periodic via holes (like in mushroom-type EBGs) behaving as conducting walls and making the strips appear as tilted horizontal corrugations. The via period as well as their locations either in the centre or at the edge of each strip are investigated. This is also done for mushroom-type EBGs. The results show that the surfaces with the largest bandgap do not necessarily have the largest bandwidth. Still, the size of the bandgap seems to be an upper limit for the bandwidth. The results show that corrugations have better performance (in terms of bandwidth and lower level of back radiation) than both strip-loaded and mushroom-type EBG surfaces, and that wide ground planes behave better than narrow ones. In addition, strips with vias are seen to have similar performance as mushrooms with via holes for TM case with respect to the surface normal, that is, transverse polarisation relative to length axis of ground plane, whereas the strip version has larger bandwidth than the mushrooms for TE case, that is longitudinal polarisation.