The Design of EBG for Enhancing the Isolation in Dual-band Microstrip Antennas

The problem of surface wave coupling between microstrip antennas especially multi-band antennas is widely studied by researchers in recent years. In this paper, a novel dual-bandgap electromagnetic bandgap (EBG) structure is proposed, which is used to improve the isolation between dual-band microstrip antennas. On the base of mushroom-like electromagnetic bandgap structure, this EBG structure is designed to suppress the surface wave, then improve the isolation between the microstrip antennas. This dual-bandgap EBG structure consists of an internal small patch, an external ring patch and two metallized vias. An equivalent LC circuit model for this EBG structure is proposed: the first LC resonance is formed by the internal patch, the vias and external patch, while the second is constructed by the internal patch, the vias, the external patch and the adjacent external patch. To analyze the dual-bandgap properties of the above equivalent circuit model, the dispersion diagram of the EBG structure based on the rectangular (irreducible) Brillouin zone in HFSS is given in this paper. In order to verify the effectiveness of this new dual-bandgap EBG structure, a dual-band microstrip patch antenna is also designed, which obtains a dual-frequency characteristic by surface slotting. Finally, the dual-bandgap EBG structure is placed between two identical dual-frequency microstrip antennas on the same layer, sharing a floor. The S21 before and after adding the EBG structure are compared. The results show that the addition of this new EBG structure can reduced the S21 of lower band by 3 dB and upper band by 9 dB, which effectively suppresses the surface waves and increases the isolation of the antennas in the two bands.