An Efficient EM-based Ultra-Wideband Bandpass Filter Design

In this paper, an efficient full wave electromagnetic (EM) design and optimization method for ultra-wideband bandpass filter is proposed. An ultra-wideband bandpass filter with 100% fractional bandwidth is designed using Sonnet EM simulator to verify the proposed method. The proposed method follows a sequential optimization process where a group of single terminated sub-networks are established by successively adding, extracting and optimizing design parameters, by using this segmented design method, only a few couplings and resonators are designed and optimized in each design stage, which improve the convergence of the whole process. Moreover, the frequency dependent couplings which are not covered in conventional coupling matrix model are well characterized by extracting the input impedance of the single terminated sub-network over the ultra-wide frequency range of interest from the reflected group delay response. The space mapping technique is employed to improve the EM based optimization process. By using the method, excellent agreement between the EM response and the design specification is obtained in the ultra-wideband bandpass filter design example.