Miniaturised frequency selective surface based on 2.5‐dimensional closed loop

Abstract

A novel frequency selective surface (FSS) has been designed based on 2.5-dimensional (2.5D) closed loop for miniaturisation. Compared with the previous FSSs in the literature, the proposed FSS is smaller (0.048λ 0 × 0.048λ 0 ) and shows almost the same transmission coefficient for different polarisations and incident angles. A prototype of the proposed FSS has been fabricated and measured. The results of the experiment show a consistency with the simulated ones.Introduction: Frequency selective surfaces (FSSs) are usually twodimensional (2D) periodic arrays, and their required frequency selective behaviours are obtained by the various resonant elements in the unit cell, such as a loop, or a dipole, or their complementary structures, or even a combination of them [1,2]. In the past decades, FSSs have been intensively investigated in the microwave and millimetre-wave frequency range, and they are widely used as antenna reflectors, radomes, spatial filters, electromagnetic bandgap materials, electromagnetic shields and so on [2][3][4]. The most important step in the design process of a desired FSS is the proper choice of resonant elements in the unit cell (which is called 'FSS element' in this Letter). In a comprehensive review of the traditional FSS elements [1], one common feature of the traditional FSS elements is that their sizes are comparable with half of a wavelength at the operating frequency [3,5]. However, the practical FSS is usually fabricated in finite dimensions, and the miniaturised FSS element is desired to enable the FSS with sufficient number of resonant elements to act as an infinite array, which lowers the sensitivity to the incident waves. To miniaturise the FSS element, different structures and methods have been proposed. For example, a miniaturised FSS consisting of a periodic array of metallic patches printed on one side of a dielectric substrate and a wire mesh printed on the other side is proposed in [5]. Closed loop and its complementary pattern are used to design a miniaturised FSS [6]. In [7], a new FSS element of spiral slots is proposed to reduce the unit cell electric size. Recently, miniaturised FSSs using complex planar topologies [8] and a novel 2.5D structure [9] are reported.In this Letter, a novel miniaturised FSS is proposed based on the 2.5D closed loop. In the FSS element or the unit cell, two pairs of the metal split square rings are printed on the top and bottom sides of the dielectric substrate. The four split square rings are connected by four metal vias in series, forming a closed loop. Compared with the traditional FSS designed with 2D loops, the proposed FSS element has a lower resonant frequency due to its longer perimeter which exhibits miniaturisation and provides favourable resonant stability at various polarisations and incident angles. To validate the performance of the proposed FSS, a prototype has been fabricated and measured. The results show a good consistency between the full-wave simulations and the measurements.

Polarisation‐independent UWB frequency selective surface based on 2.5D miniaturised hexagonal ring

“…The bandwidth of the proposed FSS is 121.6%, which is increased by 50% compared with the FSS in [7], due to the reduced inter-element spacing by 2.5D MHRs. The resonant frequency deviation of the proposed FSS at 30°incidence for the TE/TM mode is merely 0.006f 0 , where more than 50% reduction is achieved compared with the FSS in [8].…”

“…Table 1 gives a comparison of the relevant FSSs. On the basis of the FSSs in [7,8], the proposed FSS shows an improved bandwidth and polarisation-independent property. The bandwidth of the proposed FSS is 121.6%, which is increased by 50% compared with the FSS in [7], due to the reduced inter-element spacing by 2.5D MHRs.…”

Frequency Selective Surfaces: A Review

“…To overcome the limitations of conventional single layer FSSs, multilayered FSSs have been introduced, which offer additional flexibility of varying parameters for desired performance [12][13][14][15][16][17]. At present, FSSs based on fractal elements and miniaturized arrays (2.5 dimensional) are employed for compactness [18][19][20]. Three-dimensional FSS structures and active FSSs have opened new doors in microwave technology [21][22][23][24].…”

Design of a wideband square slot bandpass frequency‐selective surface using phase range analysis

“…To increase the operating BW of the bandpass FSS, a number of 2‐dimensional (D), 2.5‐D, and 3‐D topologies have been developed. In the past few years, 2.5‐D and 3‐D FSS structures have been investigated in References . These structures have an extra degree of freedom in design but at the cost of compactness and fabrication difficulties.…”