Xiaoguo Feng

A novel wideband, low-profile and second-order miniaturized band-pass frequency selective surfaces

A novel wideband, low-profile and second-order miniaturized band-pass frequency selective surface (FSS) made of metallic mesh and its complementary structures with skewed arrays of modified triples is presented in this paper. Compared with traditional second-order bandpass FSSs obtained using λ/4 apart from one another, the novel FSS with an overall thickness of λ/18 is composed of three metallic layers (the outside and middle layers are complementary) separated by two electric thin dielectric substrates. This arrangement can shorten the inter-element spacing and increase the bandwidth, while the up and bottom metallic layers can constitute a symmetric biplanar FSS and thus realize ability of maximally flat second-order bandpass response. The novel FSS has a −3 dB bandwidth about 8.2 GHz (6.9 -15.1 GHz) and a fractional bandwidth exceeds 75%. Moreover, such an FSS has the merits of stable performance for incident angles within 50° and different polarizations. The principles of operation along with guidelines for the design of the proposed FSS, the simulated results by vector modal matching method, and the experimental values of the fabricated prototype are also presented and discussed.

Tunable frequency selective surface with a shorted ring slot

In order to realize the tunable performance of a frequency selective surface (FSS), a new unit cell is designed in this paper by properly adding two metal shorts to the ring slot. Based on the spectral-domain method, the frequency responses of the FSS structure with two shorts per slot ring are analysed for both the horizontal and the vertical polarizations at the normal incidence. It is demonstrated that the presence of the metal shorts does not affect the resonant frequency of the horizontally polarized wave but doubles the resonant frequency of the vertically polarized wave. Therefore based on the analysis of the novel transmission properties, a new approach to adjusting the resonant frequency by rotating the FSS screen 90° is presented in this paper.

A novel 2nd-order bandpass MFSS filter with miniaturized structure

In order to effectively obtain a miniaturized structure and good filtering properties, we propose a novel 2nd-order bandpass metamaterial frequency selective surface (MFSS) filter which contains two capacitive layers and one inductive layer, where there are multi-loop metallic patches as shunt capacitor C and planar wire grids as series inductor L respectively. Unlike the traditional operation way—the tuned elements used in resonant surface approximately equal to one wavelength in circumference and the structure thickness with a spacing of a quarter wavelength apart, by changing the value of L and C and matching multilayer dielectric to adjust the LC coupling resonance and the resonance impedance respectively, the proposed MFSS filter can achieves a miniatured structure with ideal bandpass properties. Measurement results of the fabricated prototype of the bandpass filter (BPF) indicate that the dimension of the tuned element on resonant surface is approximately 0.025 wavelength, i.e., 0.025λ. At the same ...

Closely packed dense frequency selective surface

In order to realize wideband filtering properties of frequency selective surface (FSS), FSS of closely packed elements is presented. The Y loop elements are chosen as the graphics elements. Based on the spectral domain method, the frequency response is analyzed for different incident angles and polarizations. The result of the numerical analysis shows that the dense FSS has wide passband with better independence of angle and polarization.

The tunable property of complementary frequency selective surface with rotationally symmetric element

In this paper, the tunable property of two complementary frequency selective surface (CFSS)designs is presented. The unit cell of each design comprises of rotationally symmetric element. CFSS is a double layer structure with a patch array and an aperture array separated by a thin substrate. Simulation results prove that the resonant frequency of the two CFSSs could be tuned by rotating the patch elements. Such tunable property is explained by the electromagnetic interaction between the two complementary layers. Experimental results showed that both CFSS have good angular stability and their resonance could be tuned. Such tunable property provides a promising solution to the active FSS design.

Effective medium theory applied to frequency selective surfaces on periodic substrates

We apply the effective medium theory combined with the conventional periodic method of moments (MoM) to analyze frequency selective surfaces (FSSs) on periodic and anisotropic substrates. Based on the effective medium theory, even periodic and anisotropic substrates can be considered homogeneous; thus, the Greens function can be obtained. The resulting integral equation can then be solved by the MoM using rooftop basis functions and Galerkin testing functions. We analyze an example using this technique, and the numerical results agree with Fallahis full-vector semi-analytical method, showing an increasing difference between the results as the frequencies increase. These results show that the proposed method is effective for analyzing FSSs on periodic and anisotropic substrates.

Automatic spin coater for concave spherical substrate

Coating photoresist film with uniform thickness on concave spherical substrate (CSS) is very important for microfabrication of concave spherical optical elements by lithography technique via a laser direct writer, for the uneven photoresist film will result in ununiformity of line width so as to influence the characters of optical elements. For improving the uniformity of photoresist film coating on CSS, an automatic spin coater was designed. The process and the mathematical model of spin coating for CSS were analyzed. Difficulties for realizing the spin coater consist of the control of multi-axis motion precisely and collaboratively, valves on/ff properly and real-timely. A flexible and wellbehaved spinning motion system was achieved by tmeans of principal and subordinate CPUs control. The motion program for spin coating could be created and implemented automatically while the pressure and the valves were was watched and controlled in real time. Film coating and laser direct writing experiments on a CSS with aperture equals to 100 mm and radius equals to 370 mm were performed. Photoresist film with uniform thickness on CSS was obtained by selecting proper spin coating parameters such as rotational speed, acceleration and viscosity of the photoresist. After development, the section analysis by the atomic force microscope showed that photoresist film thickness was about 517 nm in the center and about 520 nm in the edge of substrate, the film thickness error was within 1%, and the line width was about 6.0 μm with steep sides parallel each other. Experimental results indicate that uniform thickness of thin photoresist film has been coated on CSS by the spin coater, which contributes to quality improvement of laser direct writing lines on CSS.