a power module;

an antenna array, excited by the power module, and providing a first beam group and a second beam group;

a first sensor pad, disposed adjacent to a first side of the antenna array, wherein a first capacitance is formed between the first sensor pad and the object;

a second sensor pad, disposed adjacent to a second side of the antenna array, wherein a second capacitance is formed between the second sensor pad and the object; and

a control unit, controlling the power module according to the first capacitance and the second capacitance, so as to selectively apply at least one power backoff operation to the first beam group and/or the second beam group;

wherein if the first capacitance is greater than a threshold, the control unit applies the power backoff operation to the first beam group.