Exact synthesis design theory of analogue broadband bandpass filter

In this article, an exact synthesis design procedure of broadband bandpass filter using step impedance resonator (SIR) and optimum distributed high frequency (ODHF) is presented. SIR provides a large degree-of-freedom owing to its uncomplicated implementation and broad frequency operations. It offers enormous possibilities for its practical applications as well. The filtering function in this work is extracted using the equivalent circuit model. Filtering parameters can be mapped onto Chebyshev type-I polynomials for a narrowband response. However, for broadband filter response this mapping of polynomials will not produce equiripple frequency response. Therefore, the filter polynomials are adjusted such that a required bandwidth with an equiripple response is achieved. The proposed filter structure provides compactness as well as suppression of spurious resonances at high frequencies. Moreover, for the verification purpose, the proposed filter synthesis is also applied to ODHF filter topology. To validate the proposed design procedures, a microstrip-based prototypes are realized. The simulated and measured results are found in good correlation.