High efficient and ultra-wideband polarization converter based on I-shaped metasurface for RCS reduction

Polarization being  one of the most essential features of electromagnetic (EM) waves, is crucial in a number of real- world real-world​ applications. Traditional techniques using the crystal optical activity and Faraday effect are used for polarization control, but the drawback associated with these techniques are large size, narrow bandwidth, and incident angle re- sponse, response, which make it inconsistent for many real-world applications [1], [2]. To circumvent these limitations human made structures called metamaterials having properties that are not found in naturally occurring materials are used. They are made from composite material such as metals and plastics [3]. Metamaterials have many electromagnetic applications such as perfect lens [4], perfect absorbing [5], invisibility [6], light bending [7], polarization conversion and antenna system (gain enhancement and beam steering) [8]. Due to their three dimensional (3D) nature, metamate- rials metamaterials are difficult to fabricate [9], [10]. The two dimensional (2D) version or surface counter part of metamaterial are called metasurface [8], [9], [10], [11]. Metasurface attract a lot of attention in recent year due to its reduction in size, less lossy and their strong capability in controlling the characteristic of EM wave [12], [13]. The Benefits of MS compared with bulky metamaterials, are low loss, low profile, thin thickness and easy to fabricate. Metasurface can be used as polarizer, filters, absorber [14], [15], [16]. In both modes (reflection and transmission), metasurfaces are used as cross polarizers for both linear and circular polarizer EM waves [17], [18], [19]. Recently alot of MS’s have reported but those MS’s suffer from efficiency and narrow bandwidth [20], [21]. Anyway, how to design an ultra-wideband and high-efficiency PCMS structures remains a difficult task, and further work in this area is required.

In stealth technology, broadband RCS reduction has a wide range of applications, for example RCS reduction of metallic surfaces (missile and aircraft). For RCS reduction, radar absorbent materials (RAMs) and shaping are the two primary strategies that have been used. In RAMs, EM en- ergy energy is transformed to heat through a lossy sheet, which is frequency and incidence angle dependent. Furthermore, the shaping strategy is based on changing the geometrical structure of the target to divert scattered waves away from it, which has certain disadvantages, such as changing the target geometry [22], [23]. Lately, a new approach based on the wave redirection idea has been proposed, which includes combining two distinct surfaces in a chessboard pattern, one of which is artificial magnetic conductors (AMC) and the other is perfect electric conductors (PEC) [24]. In this technique, the AMC surface acts as a perfect magnetic conductor, reflecting in-phase waves in a limited bandwidth while the PEC surface reflects out-phase waves, resulting in destructive interference cancellation and a reduction in RCS [25], [26], [27]. However, because of its limited bandwidth, its uses are limited [28].

In recent eras, another way of reducing RCS using PCMS has been proposed which converts the incident waves to its cross-polarized ones which are used in scattered waves cancellation [29], [30]. RCS reduction through polarization conversion technique was presented in [31], [32], [33] which suffers from narrow bandwidth and efficiency. Furthermore, multilayered MS were presented those achieved broadband polarization conversion and RCS reduction [34], the multi- layer multi-layer structures are difficult to fabricate and has a large thickness. It is still challenging to design ultra-wideband, high efficient, and low-profile in single layer within a simple design.

In this work, a thin, low cost, low profile, simple struc- ture, structure, high efficient and ultra-wideband PCMS is designed and fabricated for RCS reduction. The PCMS efficiently transforms linearly polarized waves into cross-polarized waves in a frequency band of 10.5 to 29.5 GHz. The PCMS and its mirror generate 180 ± 37° phase difference by placing in a triangular chessboard configuration, resulting in scattered wave cancellation and RCS reduction of 10 dB in the frequency range of 8.2 to 29.4 GHz with a FBW of 113%.

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