Miniature dual-band quadrature coupler with arbitrary power division ratios over the two bands

In this article, the design of miniature dual-band quadrature coupler that is capable of achieving arbitrary power division ratios over the two bands is presented. By employing the dual-band design of bridged-T coils, the proposed dual-band quadrature coupler features a very compact circuit size, and its power division ratio for each band can be designed with the desired value. Explicit design equations are given and practical limitations on the achievable frequency ratio and power division ratio are investigated in detail. As design examples, two 2.45/5.5-GHz dual-band quadrature couplers, one with 0/3-dB and the other with 3/3-dB power division ratios for the two bands are implemented in a commercial GaAs pHEMT process. Very compact circuit sizes of less than 2.2 mm × 1.3 mm are achieved. To the best of our knowledge, these are the smallest dual-band quadrature coupler ever reported.