Compact LTCC filter with end-coupled resonators

A compact narrow-band low temperature co-fired ceramic (LTCC) filter with a fractional bandwidth of 3% is proposed. The proposed filter consists of five cascaded half-wavelength resonators vertically arrayed on each LTCC layer. End-coupling between adjacent resonators is precisely controlled by rectangle-shaped slot on intermediate ground layer. The overall size of the filter is only 8 × 6 × 0.89 mm and a size reduction of 80% is achieved compared with a planar one. Measured S₁₁ and S₂₁ are better than -14 and -2.5 dB in the passband, respectively.