A Novel Wideband Miniaturized-Element Frequency Selective Surface

This letter presents a novel wideband miniaturized-element frequency selective surface (MEFSS). The simulation and measurement results show that the bandwidth of the proposed MEFSS is remarkably enhanced compared to that of an original second-order MEFSS while its size and total thickness are still small. A parametric study is also conducted to understand the operating mechanism of the proposed structure. The phenomenon observed in the parametric study is explained with an equivalent circuit model. 1. Introduction Frequency selective surfaces (FSSs) have been widely investigated for use as microwave and optical spatial filters in various applications. Similar to microwave circuit filters, FSSs transmit or/and reflect electromagnetic (EM) waves in certain frequency ranges. Four types of frequency responses (low-pass, high-pass, band-stop, and band-pass) can be obtained from the surfaces [1–4], but the band-stop and band-pass responses are used more frequently to achieve a precise and elaborate performance. These two window responses can be realized by etching the metallic screens with resonant geometries and their complementaries. Theoretically, the electrical sizes of the resonant structures should be comparable to half the wavelength. This physical restriction is undesirable for practical FSSs having limited dimensions, because it causes insufficiency of the unit cells (under 400 cells corresponding to ) which eventually leads to the deterioration of the desired frequency responses [1]. Various technologies have been studied in order to reduce the electrical sizes to under half the wavelength as in [5–8]. Sarabandi and Behdad, who introduced the concept in [8], are particularly notable for the square metallic patches printed on one side of a dielectric substrate and metallic cross wires printed on the other side of the identical substrate. These constitute a first-order FSS, and the electrical sizes of the elements are much smaller than half the wavelength. Although this first-order miniaturized-element FSS (MEFSS) can produce stable responses in a small area, it has a small bandwidth, low selectivity, and high insertion loss. Fortunately, these shortcomings are easily addressed by cascading the two identical first-order MEFSS layers that form a second-order MEFSS [9]. Recently, a high-resolution satellite radar system (such as synthetic aperture radar) has been intensively studied. In such an application, a multiorder MEFSS composed of multiple first-order MEFSS layers can be used as a wideband spatial filter because of its small size and simplicity.