Anterus™ RFID Solution
Signal Strength Behavior of AMX RFID Tags and Readers
The AMX RFID system tracks assets and personnel by measuring the strength of the RF signal received from a periodically transmitting badge or tag. Every reader within communication range measures the signal strength and reports it to the master controller. Most often the asset or person will be located closest to the reader reporting the strongest strength. There are, however, several environmental factors that impact the strength of the received signal. The following subsections describe these factors, present measured data, and describe the overall behavior to be expected from a system based on measurement of signal strength of a transmitted UHF radio signal.
Environmental Factors
Several environmental phenomena have potential for changing the actual received level. They are each discussed in the following sections. These effects are important to understand and keep in mind, as their net effect will typically be to make the tag appear to be farther away than it actually is. Also be aware, these factors can and do occur simultaneously and are additive in their effects.
Non-Ideal Antenna Gain
The ideal antenna would be one that transmits or receives with equal efficiency in all directions. In the real world such an antenna, with a perfectly spherical gain pattern, does not exist. Commonly used antenna types generally fall miserably short, with blind spot nulls in one or more directions. Both the badge and asset tags employ a technique referred to as diversity antennas to achieve an omnidirectional pattern that is much closer to the ideal, but still not quite the ideal perfect sphere. The reader antenna, when oriented vertically, has a
Antenna Elevation
RF signal strength loss is affected by the elevation of both the transmitting and receiving antennas above ground. In general, if either or both ends are close to the floor the received signal will be weaker. This is especially pronounced at greater distances. FIG. 8 illustrates this phenomenon. Thus, if maximum range is required by a specific application the readers should be mounted at least a couple meters above the ground.
FIG. 8 Antenna Height Influence on Received Signal Strength
8 | Anterus RFID Solution |
