A Low-Profile Decoupling Method Using the Weak Radiation of SIW-to-Microstrip Transition for Millimeter-Wave Antenna Arrays

A low profile, wideband decoupling technique utilizing the weak radiation of substrate integrated waveguide (SIW)-to-microstrip transition is proposed in this letter. The transition serves as not only the feeding of an antenna element but also the key part for generating a decoupling path. By integrating with a metal plane beneath the transitions of two antenna elements, the weak radiation of the SIW-to-microstrip transition can be extracted as an additional coupling path to achieve decoupling. This method is effective for both the E-plane and H-plane coupled antenna arrays. To explain the decoupling principle, equivalent circuits are established and analyzed. For demonstration purposes, H-plane and E-plane coupled two-element antenna arrays working around 25 GHz are fabricated and measured. The results indicate that within the operation band, the mutual coupling is reduced to lower than –30 dB for H-plane and –25 dB for E-plane coupled antenna arrays. The proposed decoupling method features a simple design procedure, wide operating band, as well as low insertion loss.