New single-layered linear-to-circular polarizers for S-band CubeSat application

Linear-to-Circular Polarizer (LCP) is considered as a simpler alternative to achieve circular polarization (CP) characteristics compared to designing CP antenna with complex topologies. LCP allows the use of linearly polarized (LP) antennas in CP with considerably higher gain and wider bandwidth for applications such as CubeSats. One of the most challenges of this application is the need for it to be sufficiently compact for operation in the S-band. An alternative is to ensure that the LCP can be stowed in a compact form during the CubeSat’s launch and be deployed for use in space. However, current polarizers are mostly designed using rigid substrates. To introduce a fully flexible and low-profile structure, two different conformal materials are used in this project to design different types of LCPs. The first is on textiles, which is a combination of felt as the substrate and ShieldIt Super as the conductive element. Similarly, the second combination also uses ShieldIt Super, and implemented on polydimethylsiloxane (PDMS) substrate. The LCPs are designed based on two categories of unit cells namely: (a) solid type (two types) and (b) loop type (two types). The polarizers are evaluated via simulations and measurements in terms of i) conversion efficiency defined by its 90% conversion efficiency limits and its and fractional bandwidth (𝐵𝑊)𝐶𝐸 and ii) axial ratio (AR) and associated fractional bandwidth, (𝐵𝑊)3 𝑑𝐵 with at least 3 dB as a limit. The four designed polarizers are categorized in terms of the number of conducting textile layers: (i) bi-layered design (three types) and (ii) single layered design (one type). The solid type unit cells are designed based on: i) a swastika-shaped unit cell sized at 51.7 × 59.8 × 3.34 mm3 ( 0.49𝜆𝑔 ×0.57𝜆𝑔 ×0.03𝜆𝑔 ); and ii) an unloaded unit cell sized at and 46×56.17×3.34 mm3 (0.60𝜆𝑔 ×0.73𝜆𝑔 ×0.04𝜆𝑔 ). On the other hand, the loop type are designed based on: iii) a crossed dodecagonal unit cell sized at 54 × 64 × 3.34 mm3 (0.51𝜆𝑔 ×0.61𝜆𝑔 ×0.03𝜆𝑔 ), and iv) a square loop unit cell sized at 48 × 46 × 3.34 mm3 (0.45𝜆𝑔 ×0.43𝜆𝑔 ×0.03𝜆𝑔 ), respectively. The dodecagonal design showed the highest (𝐵𝑊)𝐶𝐸 which is 48.12 % (from 1.578 GHz to 2.578 GHz), compared to 23.88 % (2.36 GHz to 3 GHz) and 47.34% (1.58 GHz to 2.56 GHz) shown by the unloaded and the square loop design, respectively. Meanwhile, the highest measured axial ratio bandwidth (𝐵𝑊)3 𝑑𝐵, is 33.57% (from 1.71 GHz to 2.4 GHz) exhibited by the square loop-shaped design, followed by the unloaded unit cell design with 32.64%, dodecagonal design with 29.09% and the swastika design with 1.64%. To quantify their performance when integrated with the deployment mechanism, the performance of the polarizers are additionally assessed under different bending configurations and oblique incidences. In general the loop type designs have shown higher performance than the solid type designs.