An Endfire Array Antenna for Simultaneous Operation in C- and X-Bands

In this paper, a broadband high-gain endfire array antenna based on spoof surface plasmon polaritons (SSPPs) is designed for simultaneous C- and X-band applications. To achieve endfire radiation, the SSPP structure is truncated to reduce its field confinement capability, while a radiating branch is loaded at the end of the transmission line to guide energy radiation. A rectangular metal ground is placed at the bottom of the antenna substrate to suppress backward radiation and optimize the contact area with the connector to ensure stable feeding. The final 1×4 endfire array antenna is formed by integrating unit antennas via a Wilkinson power divider-based feed network. A prototype was fabricated and tested, showing a 50% relative impedance bandwidth (6–10 GHz), 91% simulated radiation efficiency, 87% average measured radiation efficiency, and a maximum measured gain of 11.6 dBi at 9.7 GHz. With simple structure, low cost, and excellent performance, it is promising for C-band low-orbit satellite communication and X-band short-range radar.