LTCC bandpass filter based on distributed-element resonator

In this paper, two compact low temperature co-fired ceramic (LTCC) bandpass filters (BPFs) based on multi-layer distributed-element resonator are proposed. The employed half-wavelength (λg/2) resonator has been vertically folded to form a multi-layer transmission line resonator to minimize the circuit size significantly. Since there is a virtual ground in the symmetrical plane of the LTCC multi-layer resonator, the characteristic of the resonator keeps almost unchanged. For demonstration, a second-order BPF centered at 3.1GHz and a dual-mode BPF centered at 2.45GHz utilizing the proposed resonator are fabricated and measured, and the circuit sizes are 5.1×3.9×1.8 mm³ and 2.7×2.6×1.6mm³.