Millimeter-Wave Quasi-Elliptical Bandpass FSS Using Macro Cells

This work presents a collection of millimeter-wave (mmWave) quasi-elliptical bandpass frequency selective surface (FSS) designs. First, an emerging dual-mode filtering circuit with separate electric and magnetic coupling paths is established, enabling high-order bandpass and quasi-elliptical responses. Three types of long-period substrate-integrated waveguide (SIW) FSS, embedding four identical criss-cross slot elements in one period, are used to implement the circuit resonators and their coupling mechanisms. Second, a shared metal via array delineates two SIW cavities within one macro cell, forming another FSS, thus significantly improving the out-of-band suppression. Third, an improved multipath coupling circuit topology allows the designed elliptical FSS to provide an extended passband while maintaining angular stability up to 50°. Fourth, this approach can extend to developing dual- and tri-band configurations with high roll-off properties in the passband. Finally, experimental results confirm the simulations, highlighting these FSSs exhibit notable features, including low cost, low profile, low transmission loss, wide passband, and improved filtering selectivity approximating the ideal filter response.