In this paper new antennas using an open-ended substrate integrated waveguide (SIW) resonator are presented. The open-ended SIW resonator is analyzed using two different approaches. In the first approach we use the waveguide theory and in the second approach we use the transmission line (TL) based metamaterials theory. Using the SIW resonator, two antennas are designed and simulated. The first one operates at the first order resonance mode of the resonator. The operating frequency, bandwidth, maximum gain and radiation efficiency of this antenna are 8.33 GHz, 1.9%, 7.3 dBi and 94%, respectively. The second antenna which has a half mode substrate integrated waveguide (HMSIW) structure operates at the zeroth order resonance mode of the resonator. Its operating frequency, bandwidth, maximum gain and radiation efficiency are 5.72 GHz, 1.2%, 4.2 dBi and 95%, respectively. The presented antennas have advantages of low profile, easy fabrication, easy integration with other circuits and high efficiency.

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