Broadband Decoupling Network for Dual-Band Microstrip Patch Antennas

Microstrip antenna (MSA) has become one of the most popular techniques in the modern communication systems because of its potentials in diversities of operating band and polarization. With the development of highly compact circuits, the isolation between each terminal of a multi-input-multi-output (MIMO) system becomes more and more important to reach high system accuracy. Here, we propose an innovative approach of decoupling for a dual-band MSA, in which the isolation is achieved through two kinds of transmission lines based on the substrate integrated waveguide (SIW) and miniaturized spoof surface plasmon polariton (SSPP). Both SIW and SSPP transmission lines have been used in functional devices and could be considered as part of radio frequency front-end circuits. Using the proposed method, the isolation between two ports of MSA is achieved without occupying extra space. A prototype is fabricated on the basis of a triple-layer dual-band MSA, each port of which is connected to one of the novel transmission lines. Combining the perfectly high-pass SIW and low-pass SSPP, the proposed feeding network could provide broadband decoupling without influencing the property of the antenna. We show that the mutual coupling between two ports is decreased by almost 20 dB within a wide frequency band. Such a design could meet the needs in application of multiantenna or tunable system without further alteration in dimensions and has potential to play an important role in the future communication systems.