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A wideband dual-mode band-pass filter (BPF) is proposed and implemented using a vertically stacked double-ring resonator (VSDR) and a pair of broadside-coupled input/output (I/O) feeding lines based on a 4-layer low temperature cofired ceramic (LTCC) substrate. The proposed BPF is required to cover the fifth generation (5G) N77/N78/N79 band (3.3-5 GHz), thus achieves a fractional bandwidth (FBW) of 40%. Furthermore, the proposed structure not only possesses a non-orthogonal I/O feeding style for convenient interconnection with neighboring devices, but also removes disturbing element for simpler layout. Comparison and discussion are implemented as well.

A narrowband low temperature co-fired ceramic (LTCC) bandpass filter (BPF) with five cascaded physical length-reduced resonators is proposed. Each resonator is built with cascaded horizontal and vertical microstrip lines to produce slow-wave effect, which reduces the physical length of resonators for miniaturization. The entire size of the proposed BPF is only 15 × 2 × 0.3 mm, and a size reduction of 60% is achieved compared with a traditional implementation. A narrowband fractional bandwidth (FBW) of 4% and an average passband insertion loss of only 2.4 dB are achieved. Comparison and discussion are implemented as well.