Concurrent Dual-Mode Directional Coupler for Mode-Division Multiplexed Multidrop Substrate-Integrated Waveguide-Based Links

This article introduces a concurrent dual-mode directional coupler design for substrate-integrated waveguides (SIWs), which can independently excite the fundamental and second higher order modes (TE10 and TE20). We utilize this coupler to demonstrate the possibility of creating a multimode, multidrop communication link, which exploits mode orthogonality, enhancing the total channel capacity. To the best of our knowledge, this is the first realization of a concurrent multimode directional coupler in SIW technology. The coupling structure consists of four coupling nodes. Each one has two ports (one per mode), resulting in a total of eight ports. The coupling factors for the TE10 and TE20 modes are −10 dB each, allowing ten drop points along the SIW in a multidrop SIW link. The structure was fabricated using a Rogers Duroid 5880 substrate, achieving a 10-dB return loss (RL) bandwidth (BW) of more than 3.2 GHz (11.8–15 GHz) and 3.5 GHz (10–13.5 GHz) for the fundamental and second modes, respectively, corresponding to 1.7 GHz of BW for concurrent mode division multiplexing. The measured isolation between the two channels is more than 30 dB across the entire band, and the insertion loss (IL) is 1.0 and 1.5 dB, respectively. The measurement results agree well with electromagnetic simulations.