Low-Sidelobe-Level Short Leaky-Wave Antenna Based on Single-Layer PCB-Based Substrate-Integrated Image Guide

A leaky-wave antenna array with a low sidelobe level (SLL) fed by the substrate-integrated image guide (SIIG) is proposed in this letter. First, the single-layer printed circuit board (PCB) technology is applied here to fabricate the SIIG. The technology not only reduces the fabrication complexity, but also avoids the air gap between the substrate and the metallic ground. A method is introduced here to reduce the additional loss of the single-layer PCB-based SIIG caused by the air holes on the metallic cladding in the perforated regions. As the waveguide wavelength of the SIIG is short, small element spacing can be realized by utilizing this kind of feeding line. Besides, metallic strips with an optimal length-to-width ratio placed on top of the SIIG are employed as radiation elements, which exhibit strong radiation abilities and large controllable range of the leakage constant. Considering these conditions, this type of antenna can realize a low-SLL characteristic within a short length and achieve high gain at the same time. An example antenna with the vertical polarization is designed and measured to validate the theory. A single-layer transition between a coaxial probe and the SIIG is also designed to excite the antenna. The measured gain of the antenna is 14.4 dBi at 13.6 GHz with -19.2 dB SLL, and the radiation efficiency is 84.5%, considering the insertion loss of the feeding line.