Compact Fully-Packaged Hybrid CPWG/SIDGS for 1-to-4 In-Phase/Out-of-Phase Power Splitter With Low Amplitude/Phase Imbalances, Low Radiation Loss, and Good Isolation

In this paper, two miniaturized 1-to-4 in-phase/out-of-phase power splitters are proposed using fully-packaged hybrid coplanar waveguide with ground (CPWG) and substrate-integrated defected ground structure (SIDGS). The broadside-coupled stepped-impedance CPWG resonator and a pair of C-shape SIDGS resonators with fully-packaged scheme are used to implement the 1-to-4 in-phase/out-of-phase power splitter, which achieves the in-phase and out-of-phase power splitters responses simultaneously with low insertion and radiation loss. Meanwhile, a lowpass unit (LPU) embedded in the CPWG input feed-line is introduced to extend the stopband with enhanced rejection level. Then, to verify aforementioned mechanisms, an ultra-compact 1-to-4 in-phase/out-of-phase power splitter centered at 9.35 GHz with fractional bandwidth (FBW) of 26.7% is designed and fabricated. To further improve the isolation of proposed power splitter, a parallel isolation network (i.e., parallel quarter-wavelength ( $\lambda $ /4) lines with complex isolation impedance RC) located at the output ports is developed. Such a 1-to-4 in-phase/out-of-phase power splitter is then implemented and fabricated, which operates at 9.7 GHz with FBW of 47.4% and achieves 18 dB stopband rejection level up to 40 GHz. The isolations of in-phase and out-of-phase power splitters are greater than 12 dB and 15 dB, respectively, while the radiation loss remains 7% up to 40 GHz. Moreover, the passband amplitude/phase imbalances of in-phase and out-of-phase power splitters are ±0.13 dB/±0.7° and ±0.2 dB/±1.1°, respectively.