Gain-Enhanced and Size Reduction Endfire Periodic Antenna Array With Multiple DSPSL-Based Loop Resonant Element

A compact high-gain endfire loop antenna array based on a double-sided parallel stripline (DSPSL) structure is proposed in this letter. The proposed design achieves radiation mode transformation by deforming the DSPSL into two half-loops positioned on opposite sides of the substrate. A single feed port is employed, while the other port is terminated with a metal pin for impedance matching. By integrating a parasitic circular patch within the loop structure, the design effectively suppresses sidelobes and significantly enhances directionality. Furthermore, the endfire gain is further improved by incorporating a reflector behind the first radiating element. A prototype was fabricated and measured, demonstrating excellent agreement between simulated and experimental results. The measured peak gain reaches 13.57 dBi within the operating bandwidth, while maintaining a compact overall volume of only 0.19${\lambda }_0^3$.