The radiationcharacteristics of a new millimeter-wave omnidirectional circular rod antenna with doubledielectric gratins are analyzed with the rigorous mode matching method. The resultsindicate that under the condition of the same radiation intensity, the double gratingantenna has relatively smaller dimensions than that of the single one. It is undoubtedly agreat importance in the case where the limitation of the weight and volume of system isstrictly required. The effectiveness and reliability of the present analysis are verifiedby the related results given in the literature.