Design of Wideband and Compact Lumped-Element Couplers for 5G Communication

This paper presents a novel method of building multi-stage lumped co-directional couplers (LCDC) which can enhance the working bandwidth with a few elements. The method performs well in both weak-coupled and strong-coupled couplers. In order to prove the feasibility of the method, a 25 dB two-stage lumped coupler is implemented by integrated passive device (IPD) technology on high-resistivity Si substrate (HR-Si). It achieves a compact circuit size of only 0.8 mm×1.55 mm including six bonding pads. The insertion loss is less than 0.2 dB and the isolation is more than 35 dB over the frequency range from 3.3 GHz to 4.2 GHz at 5G N77 band for the coupler.