Spurious Modes Reduction in a Patch Antenna Using an EBG-Based Microstrip Transmission Line Filter

In this paper, a novel dual planar electromagnetic bandgap (DP-EBG) microstrip structure is investigated to suppress the spurious radiation of the patch antenna. It is demonstrated that the proposed structure achieves a ultra-wide stopband and excellent passband performance within a compact circuit area. Utilizing such special features, two units of the DP-EBG structure are employed in the feed line of patch antenna with the aim of suppressing harmonics and other spurious modes. The calculated and experimental results all verify that the application of this DP-EBG structure not only drastically diminishes spurious radiations of 2nd ~ 6th harmonics in a broad frequency band, but also overcomes some shortages of other EBG microstrip antennas introduced in previous research such as large back radiation or beam squint. Besides that, by adjusting the separation between the DP-EBG structure constructed in the feed line and the patch's bottom edge in a moderate distance, the procedure for designing the EBG patch antenna working on a certain frequency with the goal of reducing spurious radiation is simplified.