3D Ultra miniature MMIC TFMS 90° coupler fabricated with a standard air bridge process

This paper proposes and demonstrates a new scheme for realizing a compact 3D 90° hybrid coupler based on compact meandered air thin-film microstrip (air TFMS) transmission line sections made using a standard air bridge multi-layer InP process. This new type of air TFMS is suspended using air bridges providing a small air gap between the signal line and ground metal. The proposed coupler takes advantage of the multi-level metallization processes offered in InP technology. The intrinsic area of the fabricated 3D hybrid coupler is significantly reduced and has shown a size reduction of 80% in circuit area at 15 GHz as compared to that of a conventional hybrid coupler using the TFMS configuration. Simulated and experimental results are presented in support of the novel 3D compact coupler.