Inhomogenous material in microwave engineering: applications, realization and extraction of electromagnetic parameters

In this paper, a comprehensive study is performed on the realization of inhomogeneous materials, the extraction of the electromagnetic parameters, and the applications in microwave engineering. First, the concepts and definitions of inhomogeneous materials are presented as one of the main categories of electromagnetic complex media. Then, the applications of these materials in microwave engineering are introduced, namely gradient refractive index lenses, radar absorbing materials and radomes. In the next step, the realization methods of these materials are presented. Designing devices and achieving various applications requires intimate knowledge of the electromagnetic parameters. In the last part, the methods for retrieving and measuring the electromagnetic properties of inhomogeneous materials in the microwave frequency range are explained. Numerous articles which deal with the subject of inhomogeneous materials in microwave engineering, confirm the importance of this topic. According to the applications mentioned for inhomogeneous materials, these can be used in military and naval systems to increase the country's defense and military capabilities. Therefore, it is important to perform a comprehensive review of inhomogeneous materials in microwave engineering and to make researchers more familiar with this field and facilitate the future researches. In this research, in the form of a review article, this issue has been addressed.