A low-cost small-size 60 GHz quadrature coupler for IPD-based SiP radio systems

A reduced-size 60-GHz coplanar-waveguide (CPW) branch-line coupler has been demonstrated in integrated passive device (IPD) technology and is presented in this paper. The fabricated coupler has a size-reduction of more than 85% compared to that of a conventional CPW branch-line coupler. The size reduction is achieved by utilizing CPW transmission lines loaded with microstrip open-circuited stubs as capacitive elements. The measured results at the coupler's output ports showed a phase error of less than 3 degrees and an amplitude imbalance of less than 1.3 dB over the frequency band of 57–64 GHz. The measurements also showed an insertion loss of less 1 dB and return losses better than 14 dB over the frequency band of interest. The proposed coupler is well suited for use in low cost high performance System-in-Package (SiP) V-band radio front-ends for high data rate wireless applications.