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Manipulation of optical transmission using plasmonic nanostructures is a significant issue in applications related to ultra-compact optoelectronic devices. In this paper, we present a type of plasmonic frequency selective surface constructed with an ultrathin gold film (∼20 nm) with arrays of subwavelength holes. By means of modified nanosphere lithography, we fabricate the nanostructured gold films with scalable sizes and tunable transmission in the visible and near-infrared range. Moreover, electromagnetic simulations are performed and demonstrate good agreement with experimental results and further reveal the evolution of optical properties from the optically thick film to the ultrathin film. The research achievements will provide significant design guidance of ultrathin plasmonic frequency selective surface for future nanophotonic devices. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2171–2176, 2016

an HP-8510 C Vector Network Analyzer was used for the measurement of the proposed active BPF. The bias conditions for the GaAs-MESFET is VDS 5 3V , Vg 52 0.5 V, and IDS 5 40 mA. Under these bias conditions, low noise, stable, and high gain properties can be obtained. 4. CONCLUSION In this article, a stable low noise and high gain dual-band active BPF with GaAs-MESFET using the CRLH metamaterial has been successfully demonstrated. The proposed active BPF is connected to the gate of the GaAs-MESFET and the bias is dual bias. Then, CRLH is applied to develop a dual-band BPF using an amplifier circuit with two arbitrary frequency (x) bands. The two center frequencies of the CRLH are chosen as x1 5 1.23 GHz and x2 5 1.63 GHz, where the phase slope characteristics of the response are chosen as 290 � and 2270 � at frequencies of x1 and x2, respectively. The measurement results of the proposed active BPF are MSG values of 7.82 and 7.03 dB and the return losses of 215.1 and 210.1 dB with bandwidths of 55 (4.4%) and 105 MHz (6.4%) at the center frequencies of 1.22 and 1.61 GHz, respectively. This circuit can be fabricated using Microwave Monolithic Integrated Circuit technique due to its entirely planar structure. It can be applied to a mobile communication system. ACKNOWLEDGMENT

Two ultrawideband (UWB) bandpass filters (BPFs) using interdigital-coupled feed-line structures with different notched frequency bands are presented. The proposed interdigital lines are used, not only to realize strong coupling as feed lines, but also be able to create an adjustable rejection band in the UWB passband without adding any other circuits, which make the overall size of the filter super miniaturized. Two prototypes of the proposed notch-band UWB BPFs have been fabricated and tested, whose measured results are both in good agreement with the full-wave simulations. The notched frequency bands of these two UWB BPFs are centered at 5.8 and 8.0 GHz, with attenuation of around 12 and 14 dB, respectively. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2215–2217, 2014