A Hybrid Miniaturized-Element Frequency Selective Surface With a Third-Order Bandpass Response

A new architecture for a miniaturized-element frequency selective surface (MEFSS) capable of providing a third-order bandpass response is presented and experimentally verified. The proposed MEFSS consists of three metal layers separated from one another by two dielectric substrates. The exterior metal layers are nonresonant inductive wire grids, while the center layer is a hybrid resonator composed of an inductive wire and an I-shaped resonator. The exterior metal layers and the dielectric substrates act as two inductively coupled series resonators sandwiching the hybrid resonator layer in the middle. This results in a filter with a third-order bandpass response that can also provide an out-of-band transmission null at a frequency higher than that of the main passband. An equivalent-circuit-based synthesis procedure for this MEFSS is also presented in this letter that allows for designing the FSS from its desired system-level performance indicators (e.g., center frequency of operation, bandwidth, etc.). The validity of this design procedure is verified by presenting a design example and conducting full-wave electromagnetic simulations. Finally, an experimental proof-of-concept demonstration is performed by characterizing the unit cell of this MEFSS designed to operate in a WR-112 waveguide environment.