Transformer-Based Multisection Quadrature Coupler with 1.5 Octave Bandwidth Using GaAs-Based Integrated Passive Device Technology

This paper presents a 3-dB quadrature coupler with 1.5 octave bandwidth using integrated passive device (IPD) on gallium arsenide (GaAs) substrate. By using the multisection transformers with different coupling coefficients, wider fractional bandwidth of the 3-dB quadrature coupler can be achieved compared with previously reported techniques. The design of the transformer in each section requires maximization of the in-band quality factor to keep the number of curve intersections for S21 and S31. For validation, a 3-dB transformer-based quadrature coupler at about 1–3 GHz was designed and implemented. The proposed 3-dB quadrature coupler achieved a fractional bandwidth of 98%, which is more than twice the fractional bandwidth of an integrated coupler with at least two curve intersections for S21 and S31. Moreover, the coupler with low phase error at two-side curve-intersection frequencies for S21 and S31 can effectively separate modulation spurs in pulse-modulation systems while maintaining similar measured performance compared to the integrated quadrature couplers for sub-6GHz multiband applications.