Design of Compact Parallel-Connected Chained Function Filters

The design of compact parallel-connected chained function filters is presented in this paper. The proposed filters will offer reduced sensitivity to manufacturing tolerance within the specified bandwidth in comparison to conventional Chebyshev filters for C-band applications. A new filtering function according to a chained configuration is derived for fourth-order filters, and the synthesis procedures are presented. To demonstrate the feasibility of this approach, the circuit simulation based on parallel-connected topology is performed in an advanced design system, while the design and simulation of a fourth-order filter in dielectric technology are carried out in high-frequency simulation software. The prototype of fourth-order microstrip topology is fabricated using open-loop resonators. The overall circuit size of the filter is 2.5 cm × 4 cm. The achieved simulation and measured insertion/return loss are 0.409 dB/20 dB and 2.674 dB/18.074 dB, respectively. Extensive sensitivity analysis is conducted to prove the fabrication tolerance of the filter. The reduced sensitivity of the proposed filter to manufacturing tolerance is fully demonstrated using an open-loop microstrip technology, and its reliability is proven by theoretical analysis. The prototype results in this research are validated and agree with the theoretical results. In terms of implementation, this design technique will be a very useful mathematical tool for any filter design engineer.