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.
