| Frequency selective surfaces (FSS) have numerous applications in several microwave and optical systems. Most frequency selective surface structures have one or more dielectric substrates. In this work, instead of traditional dielectric substrates, ferrite substrates are used under different dc bias conditions. By using ferrite materials, one can change the spectral properties of these structures without physically altering them. An applied magnetic field (dc bias) on the ferrite substrate changes its properties and hence the electrical dimensions of the elements comprising the periodic structure. Thus by simply applying a dc bias, the transmission and reflection properties of the periodic structure can be changed. That leads to a tuning mechanism which allows the designer, by varying the externally applied dc magnetic field, to obtain a more desirable frequency response.; In this work, the transmission matrices for the ferrite substrate and the air, above and below the ferrite substrate are derived. By combining these transmission matrices along with the boundary conditions, the spectral domain Green's function is obtained. This process is carried out for both the in-plane bias and perpendicular bias of the ferrite. The induced current on the conductor patch is solved by the method of moments in the spectral domain. Roof toping functions are used as both expansion and test functions.; Several results are presented to show the tunability of frequency selective surfaces with ferrite substrates as a function of the applied dc bias. Other unique characteristics of the frequency selective surfaces on ferrite substrates are also presented and discussed.; The design procedure for frequency selective surfaces by neural network algorithms is introduced. |
