A scanning antenna is a scanning antenna in which antenna units U are arranged, and includes a TFT substrate including a first 
dielectric substrate, TFTs, a plurality of gate 
bus lines, source 
bus lines, and patch electrodes; a slot substrate including a second 
dielectric substrate, and a slot 
electrode formed on a first main surface of the second 
dielectric substrate; a 
liquid crystal layer LC provided between the TFT substrate and the slot substrate; and a reflective conductive plate provided opposing a second main surface of the second 
dielectric substrate opposite to the first main surface via a 
dielectric layer. The slot 
electrode includes slots arranged in correspondence with the plurality of patch electrodes, and each of the patch electrodes is connected to a drain of a corresponding TFT and is supplied with a 
data signal from a corresponding source 
bus line while selected by a scanning 
signal supplied from the gate bus line of the corresponding TFT. The frequency at which the polarity of the 
voltage applied to each of the plurality of patch electrodes is inverted is greater than or equal to 300 Hz.