Texas Instruments 2000 LF Series, Примечание к применению

Страница: 8 / 38

Lit Number: 11-06-21-068
Page (2)
1 Why Custom Antennas may be Required
There are many reasons why custom built antennas may be required:
•
special sized antennas are needed
•
the antennas have to be built into structures/ equipment e.g. doors
•
very large antenna are required e.g. road loops
•
small antennas are needed (for localized reading).
•
the antenna is for the microreader
A further reason may be to get increased read distance but the reader antenna
is just one factor amongst many that dictates reading distance. In order of
importance these factors are:
•
The size and shape of the transponder’s antenna.
•
The size and shape of the reader’s antenna
•
The electrical noise in the environment
•
The transmitter power (limited by legislation)
•
Metal in the environment
Warning:
Increasing the antenna size doesn’t automatically lead to an
increase in a tag’s reading performance –
it may reduce.
The tag’s signal must always be 6 dB stronger than any
electrical noise to ensure a successful read.
As an reader’s antenna size increases, more ambient noise
is picked up and a tag may have to move closer to the
antenna to make sure its signal is still the strongest.
Result – shorter reading distance
Texas Instrument’ antennas are optimized and, size for size, a custom antenna design
is unlikely to give a greater read range.