This article presents two new cavity-backed slot antennas utilizing substrate-integrated waveguide technology and offering high gain. Radiation performances of the proposed antennas are experimentally and numerically evaluated. Using two slots backed by a circular cavity, one can improve antenna gain by 2 dB over the gain of a single-slot antenna. Then a 2 × 2-slot antenna array backed by two cavities is presented, which offers a gain of 9.2 dBi, which is 4.2 dB and 2.2 dB higher than the gain of single- and two-slot antennas, respectively. All the proposed antenna structures are made on a single-layer substrate, and a low-cost printed circuit board process is used for fabrication.

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