Compact multilayer CPW MMIC spiral directional couplers and bandpass filters

Newly developed MMIC spiral directional couplers with tight coupling factors are designed, fabricated and characterized using multilayer CPW technology. The effects of component geometry parameters are carefully analysed using ADS Momentum. Multilayer CPW spiral couplers are reported with compact circuit size while tight coupling effect is maintained. The spiral coupler structure is applied in the design of on-chip MMIC parallel-coupled-line Marchand baluns and bandpass filters. A miniaturized bandpass filter at 2 GHz based on parallel-coupled-line theory is achieved with ultra compressed circuit size of 1 mm² and fabricated on a semi-insulating GaAs substrate with prefabricated pHEMTs. The measured results are compared to the simulated results to evaluate the effect of uncommitted pHEMTs on the same wafer.