User's Manual

WJM Series User’s Manual V01.00 www.wj.com 1/12/07 Page 8
Figure 1: MIB (Serial)
3 WJM Antennas
There are two types of antennas typically used in RFID, linear and circular
polarized. The electric field of a linear polarized antenna is constant as the wave
propagates in space. The advantage of the linear polarized antenna is a better
power transfer; this usually equates to a longer read range. However, a
polarized tag may not be in the correct orientation and therefore may receive
very little power and will not be read: for example, a vertically polarized antenna
and a horizontally polarized tag. A circularly polarized antenna is constructed in
such a way that the electric field rotates in the plane perpendicular to the
direction of wave propagation. A circularly polarized antenna is able to remove
the orientation dependency of a tag, however, the power transfer is only one half
of a similar linear antenna, as the tag will only receive its own polarization and
not the perpendicular polarization.
The WJM has the option to use an MMCX connector for connecting to an
external antenna. The WJM series is optimized for circularly or linearly polarized
antennae with linear gain not exceeding 6dBiL for either antenna.
Note: Use of other antennas not qualified with this unit may result in
harmful interference with other users and cause the unit to fail to
meet regulatory requirements. Operation with different antenna
types or the same type with higher antenna gain may violate FCC