A WLP Bandpass Filter with Ultra-wide Stopband by Transversal Signal Interference Concept

A compact and high-selective bandpass filter is proposed with an ultra-wide stopband in this paper. It is manufactured using silicon-based wafer-level packaging (WLP) technology. The main transmission path of the filter consists of a stepped-impedance resonator (SIR) loaded with three pairs of short-circuited stubs and two pairs of open-circuited stubs. By bending and coupling two pairs of short-circuited stubs, two subordinate paths are formed, which create a transmission zero (TZ) at low frequencies without disrupting the passband structure of the main transmission path, thereby greatly improving the selectivity of the filter. Additionally, in accordance with the harmonic effect, by utilizing the stopbands generated by stubs at multiple frequencies, the filter achieves a wide stopband for out-of-band rejection. The simulation and measurement results show that the BPF exhibits a minimum insertion loss of 2.6 dB and a minimum return loss of 13.9 dB. Its 3-dB bandwidth covers 9.36-13.72 GHz, and the stopband range extends from 15 GHz to 117 GHz. This confirms that the filter is capable of effectively shielding millimeter-wave signals in transceiver systems operating in traditional RF frequency bands.