Suppression-Enhanced Edge-Coupling Capacitors for Microwave and Millimeter-Wave LTCC On-Chip Single-Ended and Differential Filters

In this article, a novel suppression-enhanced edge-coupling capacitor (SEECC) is proposed for the implementation of on-chip microwave and millimeter-wave (mm-wave) filters in the low-temperature co-fired ceramic (LTCC) platform. The parasitic inductance of the quasilumped capacitor (QLC) is effectively reduced using only vertical via holes, thereby extending the spurious-free stopband. Next, SEECC-based single-ended drive resonators (SEDRs) and differential drive resonators (DDRs) are proposed to construct single-ended bandpass filters (SEBPFs) and differential bandpass filters (DBPFs) using a hybrid coupling technique (HCT). For verification, two SEBPFs operating at 8.4 and 27.3 GHz are designed, with their 20-dB stopbands up to 34.5 and 67 GHz. The 8.4- and 27.3-GHz filters achieve low insertion losses (ILs) of 0.7 and 1.2 dB. Furthermore, a 22.5-GHz DBPF with a differential-mode (DM) stopband up to 67 GHz is realized. The quasifull common-mode (CM) stopband is obtained from 0 to 67 GHz. The roll-off factor (ROF) is up to 0.4. This design concept not only contributes a universal method for harmonic suppression, low radiation effects, and quasifull (CM) rejection but also achieves a high-selectivity on-chip DBPF.