Reflectarray Pattern Optimization for Advanced Wireless Communications DOI: http://dx.doi.org/10.5772/intechopen.88909

obtained with Eq. (15). It generates a focused beam in the direction ðθ ¼ 16:5°, φ ¼ 0:0°Þ, which corresponds to a high-gain area in India. After the synthesis, the phases shown in Figure 15b were obtained for polarization X. The phases for polarization Y are similar. Once the layout has been obtained, the radiation patterns were computed using a MoM-LP tool. The copolar and crosspolar components for this initial design are shown in Figure 16 for polarization X. In this case, the minimum copolar gain is 31.5 and 28.6 dBi for zones 1 and 2, respectively. Similar results were obtained for polarization Y. Thus, the initial design complies with the

Space missions usually impose very stringent cross-polarization requirements in the form of crosspolar discrimination (XPD) and crosspolar isolation (XPI) for the transmit and receive bands, respectively. Notice that according to the definitions of minimum XPD in Eq. (4) and the XPI in Eq. (5), the XPI is a more stringent parameter than the XPDmin. The first row of Table 2 shows the values of XPDmin and XPI for both coverage zones and polarizations. The initial design presents values of those parameters between 29.5 and 33.0 dB. The goal is thus to improve the cross-polarization performance of this reflectarray by performing a direct optimization of the layout. As in the previous case,Tx and Ty are considered as optimization variables. Thus, a total of 13,097 variables will be considered. In addition, instead of minimizing the crosspolar pattern as in the previous example, now the XPDmin and XPI will be optimized as detailed in [17]. To that end, minimum masks of 37 dB are imposed for both parameters. The goal is to increase as much as possible the XPDmin and XPI while keeping the minimum copolar gain for both coverage

After the direct layout optimization, the cross-polarization performance of the reflectarray antenna significantly improved. The worst parameter is the XPI for zone 1 and polarization X, which has a value of 37.5 dB. It improved to 8 dB over the value for the initial design. The minimum improvement was 6 dB for the XPI for zone 1 and polarization X and XPDmin for zone 2 and polarization X. At the same time, the copolar minimum gain still complies with the specifications of 30 dBi for zone 1 and 26 dBi for zone 2. A summary of the performance of the initial and optimized layout may be found in Table 2. In addition, Figure 17 shows the copolar and crosspolar pattern for polarization X of the optimized layout. Since the optimization has maximized the cross-polarization performance in the two coverage areas, the maximum crosspolar values are outside both of them.

Radiation pattern of the initial layout with southern Asia coverage for polarization X: (a) copolar pattern and

requirements in both linear polarizations.

Advances in Array Optimization

zones within specifications.

Figure 16.

68

(b) crosspolar pattern.

synthesis, the layout of the reflectarray was obtained using a zero-finding routine and simulated with a MoM-LP tool. The minimum copolar gain achieved in both linear polarizations is better than 31 dBi for zone 1, while it is better than 28 dBi for zone 2. Then, a direct optimization of the layout with MoM-LP was carried out to improve the cross-polarization performance. Both the minimum crosspolar discrimination and crosspolar isolation improved at least 6 dB for both zones and linear polarizations while keeping the minimum copolar gain within requirements.

Reflectarray Pattern Optimization for Advanced Wireless Communications

The results shown here demonstrate the versatility of the proposed framework for the design and optimization of reflectarrays, as well as the feasibility of this type

This work was supported in part by the Ministerio de Ciencia, Innovación y Universidades under the project TEC2017-86619-R (ARTEINE); by the Ministerio de Economía, Industria y Competitividad under the project TEC2016-75103-C2-1-R (MYRADA); by the Gobierno del Principado de Asturias/FEDER under the project GRUPIN-IDI/2018/000191; by the Gobierno del Principado de Asturias through the Programa "Clarín" de Ayudas Postdoctorales/Marie Curie COFUND under the project ACA17-09; and by Ministerio de Educación, Cultura y Deporte/Programa de

The authors would like to thank Dr. R. Florencio, Prof. R. R. Boix and Prof. J. A. Encinar for providing the MoM-LP software for the analysis of the reflectarray cell.

\* and Marcos Rodríguez Pino<sup>2</sup>

of antenna for advanced wireless communications.

DOI: http://dx.doi.org/10.5772/intechopen.88909

Movilidad "Salvador de Madariaga" (Ref. PRX18/00424).

, Manuel Arrebola<sup>2</sup>

2 Department of Electrical Engineering, Group of Signal Theory and

Sciences, Heriot-Watt University, Edinburgh, UK

Communications, Universidad de Oviedo, Gijón, Spain

\*Address all correspondence to: arrebola@uniovi.es

provided the original work is properly cited.

1 Institute of Sensors, Signals and Systems, School of Engineering and Physical

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Acknowledgements

Thanks

Author details

71

Daniel Rodríguez Prado1

Figure 17. Radiation pattern of the optimized layout with southern Asia coverage for polarization X with improved cross-polarization performance: (a) copolar pattern and (b) crosspolar pattern.

Nevertheless, even its value has decreased, as it can be seen by comparing the crosspolar pattern of Figures 16 and 17.
