# Dual-Polarization Conversion and Coding Metasurface for Wideband Radar Cross-Section Reduction
## 1 Introduction  
Polarization converters play a crucial role in modern wireless communication due to their diverse applications, including radar cross-section (RCS) reduction [1], liquid crystal displays, and circularly polarized antennas [2]. Polarization conversion can be accomplished with the use of conventional techniques such as liquid crystals [3], birefringence wave plates [4], Faraday effects [5], etc. Many conventional techniques face limitations in real-world applications due to drawbacks such as high thickness and inadequate bandwidth. To overcome these limitations, specially constructed structures called metasurfaces (MSs) have been introduced. Metasurfaces are typically low-profile and made of lightweight materials. They offer advantages such as easy fabrication, good conversion characteristics, small size, and the ability to manipulate electromagnetic wave polarization precisely. By employing metasurfaces, the shortcomings of traditional design methods can be effectively avoided, providing a powerful tool for controlling polarization and manipulating beams. Metasurfaces have demonstrated their capability to manipulate polarization across multiple frequency regimes, including visible [6, 7], terahertz [8, 9], infrared [10], and microwave [11]. In recent years, various polarization conversion metasurfaces (PCMs)have been proposed to achieve different types of polarization conversions. These include incident and reflective orthogonal linear polarization (LP-LP) [12; 13; 14; 15], circular-to-circular polarization [16; 17; 18; 19], and linear-to-circular polarization (LP-CP) [20; 21; 22; 23]. However, many of these metasurfaces are designed to realize only a single polarization conversion function, and there are relatively few metasurfaces capable of multiple polarization conversion functions. Hence, there is an urgent need to investigate multifunctional polarization conversion metasurfaces (PCMs) across various frequency bands. Addressing this demand, the literature [22] has proposed diverse functions for polarization converters, achieving a linear polarization conversion bandwidth of up to 95.2%. [PERSON] et al. have developed a voltage-controlled reconfigurable broadband PCM capable of LP-LP and LP-CP conversions [23]. In [24], a four-band, multifunctional reflective polarization converter based on linear and circular polarizations was introduced. However, modern application systems call for integrated multifunctional devices. These devices not only minimize system size by replacing multiple components with a single multifunctional component but also reduce overall system complexity and cost. Consequently, research efforts have been focused on developing compact, cost-effective metasurfaces capable of both cross and circular polarization conversions [25; 26; 27]. One of the most efficient applications of polarization conversion metasurfaces is the reduction in the radar cross-section, which is crucial for military technologies to evade hostile radar detection. There are generally two techniques utilized to achieve lower RCS metamaterials and artificial structures. The first approach involves employing radar-absorbing materials, such as absorbers like Jaumann [28], Salisbury screens [29], magnetic absorbers [30], circuit analog absorbers [31], and frequency-selective surfaces [32; 33; 34; 35; 36], to absorb the energy of incoming waves. However, these absorbers often have limited absorption bandwidth due to their thickness and structure. Additionally, absorbing electromagnetic waves can raise the temperature and increase the likelihood of infrared light detection. Another technique to reduce the radar cross-section involves the use of diffusion metasurfaces, which scatter reflected electromagnetic waves away from their source. In this context [37], the term 'coding metasurface' was first introduced by [PERSON] et al. in 2014. The design process of a CM begins with the original design of numerous opposing phase coding elements, arranged in the most optimal feasible order.