Dual-mode Coupler with Branch-line/Rat-race Responses on Integrated Passive Device Process

Abstract

A dual-mode hybrid coupler, capable of providing distinguished functions as branch-line and rat-race couplers at two frequency bands, is first ever demonstrated on integrated passive device (IPD) process. The unusual design is fulfilled by replacing each arm of the coupler by several composite right/left-handed (CRLH) unit cells whose characteristic impedance and electrical length are controllable at two frequency bands. For size reduction, the CRLH unit cells, consist of two left-handed T-networks and a right-handed $\pi$ -network inserted in between, are realized by quasi-lumped elements on IPD process. According to experimental results, the proposed on-chip coupler provides good electrical responses as a branch-line/rat-race coupler at 1.5/2.5 GHz while occupies a very compact size of $7.15 \times 5.15 mm^{2}$.