Lumped-Distributed On-Chip Resonators With Multistubs Reused and its Application to Stopband Extended IPD Bandpass Filters

In this article, two lumped-distributed on-chip resonators are proposed by reusing multiple stubs, featuring one transmission pole (TP) and multiple transmission zeroes (TZs). Multiple open stubs are capacitively coupled at the ends of a half-wave resonator, forming multiple quarter-wave resonators for high-frequency resonances and strong capacitive coupling to achieve size reduction. Additionally, a bandstop stub is merged with an outside open stub, leading to three additional TZs with minimal change in chip size. Using gallium arsenide (GaAs) based integrated passive device (IPD) technology, two filters with center frequencies of 28 and 3.5 GHz are designed and fabricated using the proposed resonators. The 28 GHz filter achieves a low insertion loss of 0.76 dB, a small chip size, and a wide stopband extending up to 60 GHz. Similarly, the 3.5 GHz filter achieves over 15 TZs and a stopband suppression of 20 dB up to 12 octave frequencies. The results obtained from the fabricated filters demonstrate the effectiveness of the multistub reuse technique for designing ON-chip filters with extended stopbands.