Microwave and Millimeter-Wave LTCC Filters Using Discriminating Coupling for Mode Suppression

In this paper, a new discriminating coupling mechanism, which is realized by choosing suitable coupling region between the feeding lines and resonators, is proposed to suppress the unwanted resonance modes without affecting the desirable operating modes. Utilizing such a coupling mechanism, two low-temperature cofired ceramic (LTCC) bandpass filters (BPFs) are designed operating at microwave and millimeter-wave bands. One BPF realizes a wide stopband, since the third and fifth harmonics are suppressed by the discriminating coupling. The other one is an oversized 60-GHz BPF with the fundamental mode suppressed by the discriminating coupling. Due to the multilayer characteristics of the LTCC techniques, the circuit layout can be controlled flexibly to realize desirable discriminating coupling. The two filters are theoretically analyzed and implemented. Good agreement between the simulation and the measurement validates the proposed method.