A novel type of slot array antennas is presented in this article. The antenna 3-dB beam could be steered in a wide angular region, including broadside, by discrete changing of the frequency. The idea is based on radiation by different cavity modes. The proposed antenna is designed and implemented using substrate integrated waveguide technology. Grounded coplanar waveguide is used as the feed to excite different cavity modes. A single layer of low-cost printed circuit board is used for the designed antenna providing low cost, light weight, and easy integration with planar circuits. The designed antenna is fabricated and its radiation characteristics are measured. Measured results are in good agreement with those obtained by numerical investigation. The antenna provides high-gain narrow beam in addition to the advantages of compactness and simplicity of design which make it suitable in radar and satellite communications.

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