Band-pass Frequency Selective Surface for Radome Applications

Abstract

In this thesis, a most recent technique for designing low profile frequency selective surface (FSS) with second-order band-pass response is utilized. The FSS designed using this technique utilizes non-resonant sub-wavelength constituting unit cells with unit cell dimensions and periodicities on the order of 0.15λ0. It is demonstrated that using this technique, second-order FSS with an overall thickness of approximately λ0/30 can be designed. This thickness is considerably smaller than the thickness of second order FSS designed using traditional techniques (i.e. approximately λ0/4) and could be particularly useful at lower frequencies with long wavelengths. Designing of FSS with frequency response that is insensitive to angles of incidence and polarizations is a challenging job. In this technique of designing FSS, combination of small thickness and miniaturized unit cell dimensions ensures that the frequency response of the structure does not significantly vary as a function of the angle of incidence. To facilitate the design of this structure, an equivalent circuit based synthesis method is also presented in this thesis. Different bandpass FSSs operating at X and Ku bands were designed and simulated. Out of these two designs FSS operating at X-band was fabricated and tested. A free space measurement setup is used to thoroughly characterize the frequency response of this prototype for both the TE and TM polarizations and various angles of incidence. By the comparison of simulated and measured results, it is observed that there exists a high insertion loss in the measured result, and in the measured result the desired frequency band is also shifted backward. This high insertion loss and band shifting in the measured result are due to the absence of required measurement setup and variations in the dielectric constant of FR4 substrate. A detailed design procedure, principles of operation and simulated and measured results are presented and discussed in this thesis report.