An antenna for suppressing the gain of side lobes includes a substrate, tandem antenna units arranged on the substrate and each including a first feed line and radiating elements, and the width of the radiating elements decreasing gradually from the middle of the first feed line to the two ends; and a power divider disposed on the substrate and including a feeding port, a second feed line with middle connected to the feeding port, and transmission lines, connected to the second feed line respectively. The output powers of the transmission lines decrease gradually from the middle of the second feed line to the two ends, and the transmission lines are respectively connected to the first feed lines. Thereby, the present invention can effectively suppress the gain of the side lobe both in YZ plane and the XZ plane, and improve target detection.