User's Manual

COBALT UHF-SERIES CHAPTER 9: RFID OVERVIEW
PAGE 131 OF 140
Furthermore, the Cobalt UHF antennas feature a 3dB Beamwidth, 63° or 65°,
providing a large reading zone.
Figure 9-4: Circular Polarized Antenna’s Reading Range
As considered above, the ability for signals to propagate within environment is
dependent on the signal wavelength, and hence frequency. UHF will have challenges
with crowded environments: within warehouses, truck yards, and other facilities, the
ability for an RFID system to operate in and around obstructions is critical.
These obstructions are often metallic, such as vehicles and metal shelving racks,
requiring signals to propagate “around” rather than “through” the obstructions. For
that reason, for industrial applications involving significant environmental obstructions
HF is a preferred frequency.
At UHF frequencies, multi-path RF waves caused by reflections from the floor and
other obstructions may combine constructively or destructively. When these signals
are in-phase they combine to give a stronger signal, but when out-of-phase, they
cancel and create ‘reading holes that get worse with distance from the antenna.
Therefore, referring to the picture above:
Tags A and D are in strong zones and will read.
Tag B will read if its antenna is long enough to ‘span the gap’
Tag C and E will not read
3 DB BEAM WIDTH
A B
0.5 0.6
1.0 1.3
1.5 2.0
2.0 2.6
2.5 3.1
3.0 3.7