In this paper, novel cavity-backed slot antennas based on substrate-integrated waveguide (SIW) for dual frequency and bandwidth enhancement are proposed. Their performance is numerically evaluated by means of the method of finite elements. Using metalized via holes at the middle of a SIW cavity, resonate frequency of TM010 mode is shifted up. With placing a slot at one side of the cavity, electromagnetic fields are radiated thorough the slot at two resonate frequencies of TM010 and TM110 modes. Proposed antenna operate at 9.68 GHz and 10.28 GHz with impedance bandwidths of 60 MHz and 80 MHz for S11<-10 dB respectively and it provides gain of at least 4.6 dB. Moreover, by merging two modes, bandwidth of the structure would be improved. All antenna structures are made of a single-layer substrate and are fed by a 50 Ω microstrip line. The proposed antennas are compact, low-cost and present high radiation efficiency.

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