Quasi-normal mode theory applied to elliptic-filter metasurface design

We present universal analytical criteria for the quasi-normal modes (resonances) of lossless reciprocal 2-port systems to systematically design symmetric or “antimetric” scattering responses, emphasizing compact high-order standard filters. As an application, we design microwave metasurface bandpass or bandstop elliptic filters with various orders and bandwidths.