12.1.2015
Idesco Oy
Emission Patterns
Readers and Transponders
•
EPC reader emits radio waves outward in the shape of a cone.
–
The beam cone expands outward, vertically and horizontally,
at an angle of 65° off of the plane of the reader.
•
The reader’s antenna only transmits effectively forward.
–
Backward and side scatter emission is so weak that reliable reading
at those angles is less than 1 meter. Environmental reflections at
a site might sometimes give better results but they are
only
due to
those reflections and not the emission pattern of the reader.
•
Transactions occur when this pattern overlaps with the tag,
providing the chip enough power to reply to the reader.
•
EPC Windshield Labels reply with emissions in 360 degrees around their axes; amplitude is
strongest perpendicular to the tag axis.
–
At angles approaching parallel to the tag’s axis, the strength of the reply gets weaker, until the tag doesn’t
emit at all in directions parallel to its axis.
–
Because of these patterns, a reader installed above a lane reads horizontally-installed tags more reliably than
if it’s installed on the side of the lane.
•
The pattern of 3D Frog Labels is omnidirectional (360 degrees to every direction), so tag position
doesn’t impact its reading reliability.
