Gómez-García, Roberto, Sánchez-Soriano, Miguel Ángel, Sánchez-Renedo, Manuel, Torregrosa-Penalva, Germán, Bronchalo, Enrique
Low-Pass and Bandpass Filters With Ultra-Broad Stopband Bandwidth Based on Directional Couplers
IEEE Transactions on Microwave Theory and Techniques. 2013, 61(12): 4365-4375. doi:10.1109/TMTT.2013.2281965
URI: http://hdl.handle.net/10045/53914
DOI: 10.1109/TMTT.2013.2281965
ISSN: 0018-9480 (Print)
Abstract: 
The design of planar sharp-rejection low-pass and bandpass filters (LPFs and BPFs) featuring a very broad stopband is addressed in this paper. For the LPF case, two new classes of bandstop signal-interference transversal filtering section (TFS) consisting of power directional couplers in reflection mode are proposed. In the BPF application, additional short-circuit stubs are inserted at the TFS input/output accesses. Based on these filtering cells, the devised LPF and BPF approaches are then derived from the cascade of multiple TFSs with frequency-contiguous stopbands. Thus, an overall attenuated band showing an ultra-large spectral width and deep rejection levels through the generation of several transmission zeros (TZs) is synthesized. Furthermore, such unprecedented filtering performances are obtained for much lower circuit complexity than available solutions. The operating principle of the conceived LPF and BPF topologies and guidelines for their realization are detailed. This includes formulas for their analytically designable TZs. For practical validation, three LPF prototypes and one wideband BPF circuit are also fabricated in microstrip technology and tested.
Keywords:Bandpass filter (BPF), Bandstop filter (BSF), Branch-line hybrid, Directional coupler, Hybrid ring, Low-pass filter (LPF), Microstrip filter, Signal interference, Transmission zero (TZ), Transversal filtering section (TFS), Wideband filter
IEEE
info:eu-repo/semantics/article