Design of microwave MCM-D CPW quadrature couplers and power dividers in X-, Ku- and Ka-band

The successful design and measurement of high-performance coplanar waveguide (CPW) quadrature hybrid couplers integrated in MCM-D at Ku and Ka-band and a Wilkinson power divider at X-band is discussed. We have investigated the feasibility of integrating 3-dB quadrature couplers in our MCM-D technology. Quadrature couplers based on two edge-coupled lines are not practical, as the required line-dimensions are too small. As an alternative, couplers using re-entrant sections and CPW Lange couplers have been realized. For the Lange coupler, we have obtained in the 10.5-14.5 GHz band: a return loss and isolation better than 20 dB, an amplitude balance below 0.13 dB and a phase balance of (90 +/- 1) deg. For the coupler using re-entrant sections, we have obtained in the 20-30 GHz band: a return loss better than 17 dB, isolation better than 20 dB, an amplitude balance below 0.25 dB and a phase-balance of(90 +/- 2.5) deg. A trade-off between these two design-approaches for integration in MCM-D is given. A first Wilkinson power-divider at X-band has also been designed and measured to verify the accuracy of the in-house models. Excellent agreement has been found up to 50 GHz.