LTCC Bandpass Filter Chips With Controllable Transmission Zeros and Bandwidths Using Stepped-Impedance Stubs

A novel bandpass filter (BPF) chip using stepped-impedance stubs (SISs) embedded in coupled lines (CLs) based on the low-temperature cofired ceramic (LTCC) technology is proposed in this brief. The controllable bandwidth (BW) is mainly realized by the wide range of variable coupling strength of the broadside CLs, and the controllable transmission zeros (TZs) can be generated by SISs to obtain high selectivity. Furthermore, in order to obtain a general design method for the proposed BPF with different BWs, the analytical (closed-form) process based on the even- and odd- mode analysis method is presented. For verification, a prototype for the proposed BPF operating at 3.5 GHz with the 3-dB fractional bandwidth (FBW) of 32.0% is designed, simulated, fabricated, and measured, respectively. Finally, the measured results that are in good agreement with the simulation show good performance of the proposed circuit.