A novel reduced-size 60-GHz 180° coupler using LG-CPW transmission lines

A compact reduced size 60-GHz band (57-64 GHz ) 180° coupler is proposed and implemented in an IPD (Integrated Passive Devices) technology. A size reduction of 75% compared to a conventional 180° coupler has been obtained by using high impedance lower-ground coplanar waveguide (LG-CPW) transmission lines loaded with microstrip open-circuited stubs. The measured results of the coupler showed an amplitude imbalance of less than 0.5 dB and a phase variation from 187° to 184° over a frequency range of 57-64 GHz. The measured return loss is better than 15 dB and the isolation is greater than 24 dB over the frequency band of interest. The measured results confirm the potential of the proposed coupler for low-cost, high-performance, small-size transceiver front-ends for high data rate wireless systems operating in the unlicensed 60-band.