Design of Ultra-wideband 3dB Quadrature Coupler MMIC

In this paper, a 2∼18GHz ultra-broadband 3dB quadrature coupler that achieves 160% fractional bandwidth exceeding three octaves using monolithic microwave integrated circuit (MMIC) technology was proposed. The directional coupler adopts the unequal tandem construction, and this design approach minimizes the needed coupling coefficients and thus reduces design difficulty. Furthermore, a method of parallel capacitance between the coupled lines is also utilized to enhance the coupling and minimize the size of the microstrip lines. The coupler was designed based on the Win Semiconductor Gallium Arsenide (GaAs) H02U process environment. EM simulation results show that the amplitude imbalance within operating frequency is less than 3.5dB, the phase imbalance is no more than 7 degrees.