K-Band Graphene-Based Electrically Tunable Hybrid Coupler

This work presents the design, implementation, and characterisation of an electrically tunable quadrature hybrid coupler. The design exploits a lumped-element configuration which utilizes four metal-insulator-graphene diodes to minimise the footprint. The fabricated prototype is realised on a thinfilm flexible polyimide (PI) substrate. The assessment of the fabricated circuit reveals a good and wideband S11 performance and an S21 measurement of −4.2 dB with a tolerance of 0.2 dB across the frequency band of 18–27 GHz. The introduced thin-film technology promotes the realisation of flexible compact reconfigurable transceivers that cover several frequency bands.