Manipulating asymptotic frequency and transition in spoof Plasmonic Metamaterials via Folded Microstrip Spur-lines

This work presents an approach to realize the spoof plasmonic metamaterials with both controllable asymptotic frequency and controllable transition from the passband to the stopband. Folded microstrip spur-lines are introduced to construct the unit cells. Dispersion and transition properties are firstly analyzed to investigate the effects of the folded microstrip spur-lines, and the influence of the geometrical parameters of the proposed unit cell on the asymptotic frequency and transmission zero is studied. Then, a spoof surface plasmon polariton (SSPP) low-pass filter (LPF) is designed and implemented based on the proposed unit cell. Finally, the proposed LPF`s transmission characteristics are simulated, fabricated, and measured, confirming the feasibility of the strategy. Both reduced size and sharpened transition can be realized jointly by the extra degrees of freedom provided by the folded microstrip spur-lines. The proposed strategy can greatly accelerate the development of versatile microwave integrated circuits and systems based on spoof plasmonic metamaterials.