A Compact Single-Layer Septuple-Mode Wideband Filtering Antenna and Its Application for Antenna Array

In this article, a septuple-mode wideband filtering antenna on a single-layer substrate with a simple and compact layout is proposed, together with its application to antenna array. Based on the theoretical field analysis, the circular patch resonator and the square substrate integrated waveguide (SIW) cavity are firstly combined, thereby obtaining three in-band resonances and one out-of-band radiation null without enlarged structural dimensions. Subsequently, slots are strategically introduced along their radiation edges to create two additional modes per resonator. By properly arranging these modes, a septuple-mode wide bandwidth with three out-of-band radiation nulls is formed. Compared to the conventional circular patch antenna, the proposed design achieves an expanded bandwidth of 25.35% in fraction with stable radiation (approximately 4.87 times wider) and improved out-of-band performance, while maintaining the same single layer structure and nearly identical dimensions. Furthermore, owing to the tightly arrayed shorting pins around the antenna and internal arrangement of its radiation boundaries, the antenna can be compactly integrated with zero spacing in array design. For validation, both the standalone antenna and a 2×2 antenna array are fabricated and measured, confirming successful realization of bandwidth enhancement and filtering function integration, along with structural advantages of simple layout and compact size.