The dispersion diagram of infinite periodic structures is useful for the practical design of waveguide filters. Analyzing the pass- and stop-bands (gaps) in the dispersion diagram of a unit cell, it is possible to generate a finite structure with a very similar electrical response. However, the truncation of the infinite periodic structure degrades the pass-band performance. In this paper, these impairments are overcome by means of suitable waveguide tapers matching the impedance of the periodic structure to the access ports. As a result, the analysis and design of practical low-pass filters, derived from passive structures based on Electromagnetic Band-Gap (EBG) waveguides periodically loaded with metal ridges, are successfully addressed. According to these procedures, a five-order and an eight-order EBG low-pass filters are obtained after an optimization step. Measurements of a manufactured prototype fully validate the proposed approach.
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