## 4 Discussion  
To verify the performance of the proposed polarizer, fabrication was carried out on a 0.127 mm thick, flexible Rogers-5880 substrate using LPKF E33. Before carrying out fabrication, we made sure that the machine's precision would not deteriorate the response of the converter by carrying out a sensitivity analysis. An array consisting of 30 \(\times\) 30 unit cells was fabricated. A picture of the fabricated sample is presented in Figure 5a. To perform measurements for the polarizer, a pair of ultra-band transmit and receive antenna covering both operational bands were needed. Due to the unavailability of such antennas, measurements were completed in two sets using two different antennas. For Ku band measurements, two broadband patch antennas covering the required band of operation (11.05-16.75 GHz) were used. For measurements in the Ka band, a set of standard circular horn antennas operating in the 26.5-40 GHz frequency band were used. For the measurements of the transmission parameters of the proposed structure, an AV3672C vector network analyzer (VNA) was used. The measurement setup for the proposed converter was as shown in Figure 5b,c for the Ku and Ka bands, respectively. For measurements, a free-space characterization technique was used. After calibrating the network analyzer, the first step in free-space characterization, the reference measurements were taken. Then, as a next step, the fabricated polarizer was placed in between the transmit and receive antennas. It was ensured that the placement of the polarizer was in the line of sight of the antennas. Subsequently, measurements for linear transmission components \(|\)txx\(|\) and \(|\)txy\(|\) and their respective phases were carried out. To determine the cross-linearly polarized components (txy), the receive antenna was rotated 90 degrees. Figure 4: Surface current phenomenon in the proposed structure at 13.58 GHz: (**a**) t = 0, (**b**) t = T/4, (**c**) t = T/2, (**d**) t = 3T/4; and at 40 GHz: (**e**) t = 0, (**f**) t = T/4, (**g**) t = T/2, (**h**) t = 3T/4. As the last step, \(|\) txx\(|\) and \(|\) txy\(|\) were calculated by determining the difference between the linear transmission components and reference measurements. Furthermore, their phases were calculated by subtracting them from reference phases. In this way, losses due to surroundings and measuring cables were compensated. Finally, the measured results were as presented in Figure 6a-c. The measured performance in the first band of operation (Ku band) agreed well with the simulated axial ratio results, with AR values in the range from 1.5 dB to 3.5 dB and simulated values from 1.2 dB to 3.0 dB. Although the measured values of the AR in the second band of operation (Ka band) were higher than the simulated values, the trend was nevertheless the same. In the Ka band, the values of AR were in the range from 2.0 to 4.0 dB and the simulated values in the range from 1.5 to 3.0 dB. It was assumed that the frequency shift in the Ka band of operations might have been due to the fabrication tolerance of LPKF E33. Higher frequency implies more sensitivity towards minute changes in dimensions; meaning that the Ka band was more sensitive than the Ku band. This slight shift in operating frequency band may have been the result of small changes in the dimensions during fabrication of the prototype polarizer. Moreover, the non-ideal conditions, such as the finite array size of the fabricated structure as compared to the infinite array in simulations, and non-ideal experimental conditions are the reasons behind the differences in the simulated and measured results. The comparison of the proposed structure with other already presented dual-band MS-based polarizers is presented in Table 2. The structure performed over the widest dual  
Figure 5: (a) Fabricated polarizer. (b) Ku band and (c) Ka band test setup for the polarizer. Figure 6: (a) Measured axial ratio response; (b) AR within Ku operational band; (c) AR within Ka operational band.