Dielectric backed conducting strips as inductive element in spatial band-pass filter design


Abstract: In this paper a new method has been presented to design spatial band-pass filters consisting of dielectric backed conducting strips. This approach uses an equivalent circuit model in which determined inductive elements are spaced at intervals about half wavelength. To realize the proposed method, the inductive elements have been replaced by dielectric backed conducting strips located at intervals about half wavelength. Half wavelength transmission line sections act as resonators. In this manner the wideness and spacing of strips in each dielectric backed conducting strip, as well as the distance between them, is determined by fitting the characteristic (transfer function) of the proposed filter to that of a desired one obtained from an equivalent circuit model. To take the effect of higher order modes (evanescent mode), a coupled set of magnetic field integral equations is derived and formulated. Finally a set of linear matrix equations are solved using method of moments (MoM) and entire basis functions have been used resulting in rapid convergence. The usefulness of the proposed structure and its performance are verified by designing and simulating an equal ripple Chebyshev-type and a Butterworth-type spatial band-pass filter.

Keywords: Spatial band-pass filters, frequency selective surfaces, coupled magnetic field integral equations

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