Two-parameter Capacitance Compensation for Quasi-ideal Directional Coupler Design in Package Substrate

A 3 dB half-hermetic packaged directional coupler is designed in multilayer package substrate using two-parameter capacitance compensation method in this paper. Two kinds of capacitance, which are only added to one of the two coupling lines, are introduced to solve port matching and coupling coefficient inequality between capacitive and inductive coupling. The designed 3 dB coupler has a relative bandwidth of 84% with center frequency of 6 GHz within the range of ±1.5 dB amplitude imbalance and ± 0.6° phase deviation. The design can be directly mounted on printed circuit board and used for compact SoP applications.