Non-contact IC media capable of performing communication of information stored therein in a noncontact manner are conventionally utilized. Such non-contact IC media include a medium using a UHF band available for long-distance communication. In most cases, a single-element patch antenna is often used as an antenna for communicating with the non-contact IC medium using the UHF band. The single-element patch antenna has a half-power width (beamwidth) as broad as about 70 and therefore has the advantage of reading information from the non-contact IC media in a broad area.
However, in some cases, only the non-contact IC medium within a specific area need to be read. Particularly, such cases include, for example, a case that, under the situation where articles are transported while undergoing a plurality of working stages, only the non-contact IC medium of the article in one working operation need to be read.
In this case, it is considered to use an antenna with a narrow half-power width. However, such an antenna needs to be extremely large in size, like a multiple-element array antenna and a parabola antenna.
Meanwhile, there has been proposed a tag communication device that calculates the position of a non-contact IC medium on the basis of estimated incoming direction of a radio wave from the non-contact IC medium (see Patent Literature 1). The tag communication device applies different weights to outputs of antenna elements to detect the intensity of the radio wave in a specific direction.
However, the tag communication device requires complicated calculations in order to find the direction where the one non-contact IC medium exists.