Tag performance is affected by the orientation of the tag relative to the interrogator antenna. The best tag orientation occurs when the tag plane and the antenna plane are parallel to each other. At this orientation, the tags receive the maximum power. As the tag is rotated, it presents a smaller effective area to the incoming radio waves and thus collects less power. The tag read range decreases as the collected power decreases.
Most passive UHF tags have a single dipole antenna that has nulls along its north and south poles. This type of tag cannot be read when the axis of the poles on the tag antenna is perpendicular to the plane of the interrogator antenna. Two options are available to remedy this situation: install two interrogator antennas—one perpendicular to the other—so the tag antenna axis is not perpendicular to the plane of at least one of the interrogator antennas. Or, use tags with two dipole antennas (a dual dipole tag), with one antenna perpendicular to the other. The axis of at least one of the two antennas on this tag will never be perpendicular to the interrogator antenna plane.
The location of the tag within the IZ also affects the tag’s performance. As the tag moves away from the interrogator antenna, it receives less and less power. The reflected signals mixing with the original signal further reduces the power available to the tag. At the outer edges of the IZ, signal strength may decrease in pockets to such a low degree that the tag may not be powered and the consistency of the tag read decreases.