Frequency Selective Surface With Miniaturized Elements Based on Quarter-Mode Substrate Integrated Waveguide Cavity With Two Poles

A frequency selective surface (FSS) with miniaturized elements based on a quarter-mode substrate integrated waveguide (QMSIW) is proposed and investigated in this paper. The periodic element includes the QMSIW cavity and two L-type slots etched on the top and bottom conductor claddings of the cavity. The slot not only performs as the equivalent magnetic wall of the QMSIW FSS element but also provides a pole near the resonant frequency of the QMSIW cavity to improve the passband characteristics of the FSS. In this case, the size of the conventional FSS element can be reduced by 65% at the same operation frequency while keeping a similar performance. Based on this miniaturized element, the frequency interval between the passband and the first parasitic passband can increase 2.7 times compared with that of a conventional SIW FSS. As an example, an X-band QMSIW FSS is designed, fabricated, and measured. Besides, it is insensitive to the incident angle and polarization of the incident wave. Such a miniaturized FSS element can also be employed in the design of a multiband FSS with controllable transmission zeroes.