Fourth-Order Bandpass Filter Using Dual-Mode Ring Resonator and Parallel-Coupled Lines

A fourth-order bandpass filter using dual-mode ring resonator and parallel-coupled lines loaded with half-wavelength open stubs is presented in this paper. Six transmission zeros (TZs) and four transmission poles (TPs) from 0 to 2f0(f0 denotes center frequency of the filter passband) can be achieved with the help of two open stubs and open coupled lines, where two TZs are generated by the loaded two open stubs. Finally, a verified physical layout of the proposed filter is designed and simulated with good frequency selectivity, whose ADS and HFSS simulations are in good agreement.