A switchable radiator includes a dielectric substrate, a first conductive layer having a slot disposed over an upper surface of the dielectric substrate, a tunable dielectric layer disposed over the first conductive layer, and a second conductive layer disposed over the tunable dielectric layer. The tunable dielectric layer has a first dielectric constant at a first DC voltage and a second dielectric constant at a second DC voltage. The second conductive layer includes a first signal section, a second signal section, and an impedance-matching section connecting the first signal section and the second signal section. The operation method of the switchable radiator includes applying a first DC voltage to the tunable dielectric layer to enable the switchable radiator to radiate energy through the slot and applying a second DC voltage to the tunable dielectric layer to disable the switchable radiator from radiating energy through the slot.