Novel Transmission-Line Circuit Configuration of Cross-Coupled Filter With Negative Coupling

This article presents a new quadruplet filter structure with a negative coupling capable of producing a pair of transmission zeros (TZs). More specifically, the presented structure is composed of coupled-lines and standalone lines, whose parameters are fully given in terms of the normalized coupling values, the center frequency, and the bandwidth. Hence, a filter design using our quadruplet filter schematic does not necessitate carrying out the coupling tests for finding initial dimensions of the lines constituting a filter. In addition, the length of all coupled-lines and standalone lines is a quarter wavelength, which makes a filter have no undesirable resonant peaks close to the passband. For demonstrating the presented filter structure, this work also provides the discussion on a microstrip filter example centered at 2 GHz having 7.5% bandwidth.