Compact and High-Efficient Air-Filled Substrate Integrated Waveguide Broadband Endfire Leaky Wave Antenna

The air-filled substrate integrated waveguide (AFSIW) millimeter wave (MMW) broadband endfire leaky wave antenna (LWA) with compact and high efficiency is proposed in this communication. The antenna mainly includes a three-layer substrate. The first and third layers are the radiation main body, and the second layer is an AFSIW transmission line (TL). First, the AFSIW with air reduces the dielectric losses, thus improving the radiation efficiency of the antenna. Second, the AFSIW has weak dispersion characteristics, benefiting the wide operating bandwidth of the antenna. Additionally, a double-sided diamond-shaped slot exhibits a flatter phase constant in the slow wave region, further enhancing the antenna’s operating bandwidth. The electromagnetic energy of the AFSIW endfire LWA 1 is concentrated on the metal layer surface through a single diamond-shaped slot array, achieving endfire radiation along the waveguide structure. By utilizing the confinement of the dielectric layer on the field, the gain of the antenna is further improved. Finally, the AFSIW endfire LWA 2 utilizes multiple diamond-shaped slots as the unit cell, increasing the unit cell’s attenuation constant and further enhancing the radiation efficiency of the antenna. The prototypes of LWA are fabricated and tested. The measurement results show that the impedance bandwidth of LWA 2 is 29–42 GHz. The maximum radiation efficiency of LWA 2 is 90.3%.