Low-Profile High-Gain Surface Wave-Based Endfire Antenna With No Beam Tilt

Conventional ground-backed endfire antennas suffer from beam tilt, undermining forward-looking radar performance. This work proposes a compact surface wave-based endfire antenna that preserves a rigorously endfire main beam without tilt. The antenna comprises a ground-backed periodic Jerusalem cross (J-cross) array and an inverted-L antenna (ILA) accompanied by four parasitic strips. The J-crosses are deliberately designed to support the requisite transverse electric (TE) surface waves. Excited by the ILA, these surface waves propagate along the J-crosses which are periodically resonant. By tuning the phase constant, within each period, the currents in opposite directions appear in pairs, cancelling radiation in the broadside direction, yielding a bidirectional radiating element with no beam tilt. Assembling these elements into an array, the proposed antenna realizes the bidirectional endfire radiation pattern with no beam tilt. To further enhance the gain, parasitic strips are strategically positioned above the J-cross array with added periods. Strongly coupled to the J-crosses, these parasitic elements act as directors and reflectors, imposing phase shifts on the array and reinforcing radiation in a single endfire direction. The operating principle of the proposed antenna is analyzed thoroughly. Experimental results demonstrate impedance bandwidth ranging from 5.74 to 5.84 GHz and maximum gain of 10.0 dBi at 5.79 GHz. The antenna maintains a main beam precisely aligned with the endfire direction across the band. The antenna achieves notably high gain with a low profile of 0.034λ and a compact footprint of 2.44λ × 0.37λ, where λ is the wavelength at 5.8 GHz. Hence, the proposed antenna is well suited for forward-looking radar on high-speed platforms with constrained frontal area.