A compact LTCC bandpass filter using resonators loaded with spiral-shaped open-circuited stubs

In this article, a new compact multi-layer low temperature co-fired ceramic (LTCC) bandpass filter is proposed. It is composed of two quarter-wavelength resonators and a K-inverter. The resonators are loaded with two open-circuited stubs, giving an advantage in size-reduction and control of the spurious responses. The K-inverter is composed of two short-circuited stubs whose value can be adjusted by changing their length and width. There is no via-hole in the proposed filter structure, so the fabrication process is simple. The grounding of the resonators and inverters is done by connecting them to the side ground. The fabricated filter has a wide upper stop-band characteristic and the total filter size is 2.0×1.2×1.1 mm.