antenna design of rfid
Criteria for the design consideration
1. What is the Read Distance Required?
A single antenna 500-mm x 500-mm has a reading range of about 600-mm at 4W with the large HF-I inlay. A pair of similar antennas (connected to the same reader) can cover distances greater than 1m. With larger antennas and greater power outputs, longer reading distances can be achieved. Integrators are advised though, that they should always build a margin of safety into their designs when specifying maximum read performance HF-I inlays will Read and Write at the same distance but the original HF inlays will only Write at around 70% of the reading distance.
2 What is the Inlay Orientation?
Inlays receive power by magnetic coupling with the antenna and will receive maximum power when in their best orientation.
3 At What Speed is the Inlay Traveling?
At a baud rate of 115,200 the S6500 Reader will read a single block, approximately 60
times a second. Writing, reading multiple blocks and Simultaneous Identification,
have different timings and the designer must ensure that, whatever speed the inlay is
moving at, it is in the magnetic field long enough for the complete transaction to take
place. High-speed operations may require a lengthened antenna.
4 What is the Inlay Separation?
The ability to read closely separated inlays depends on the width of the antenna but is
closely tied in with inlay reading speed. When multiple inlays are likely to be in the
field at the same time and simultaneous identification is used, more time will be
required than when reading singulated inlays.
5 How Much Data is Required?
The more data that is required from the inlay, the greater the time the inlay must be
within the field of an antenna, which in turn will be related to the speed the inlay is
traveling.
1.What are the Governmental (PTT/FCC) limits?
Systems Integrators should consult their local Governmental Agencies / Test houses
to determine the legal limits for the RF field generated from an antenna. The system
is approved in both Europe and USA using 4W into the standard 300-mm x 300-mm
antenna but where larger antennas are required; they may need to be shielded to
meet local regulations.
ETSI Regulations can be found in EN 300 330 or FCC Regulations can be found in
FCC CFR47 Part 15.
2 Is there Electrical Noise?
Problems with electrical noise are rare but it is wise to perform a site survey before
commencing antenna design, than struggle to solve a problem later. In general
electrical noise tends to influence the receive performance and results in reduced
reading ranges. Slight changes in antenna orientation to the noise source, additional
grounding or shielding can all help to reduce the effects. If the problem is common
mode noise, fitting a BAlanced UNbalanced (BALUN) transformer will help.
3 Is there Metal in the Environment?
The presence of metal close to an antenna will reduce its performance to some
extent. As the antenna size increases, so does the minimum separation distance
from metal before de-tuning effects are noticed. Much of the effect can be ‘Tuned out’
but when the metal is close, e.g. less than 200-m, the metal will absorb some power
and the read distance will drop. Antennas should always to be tuned in their final
positions.
4. Proximity of other Antennas
The presence of other antennas will alter the way a system performs because of
coupling between the antennas. In some cases, e.g. reflective passive antennas
(covered later), the coupling will be deliberate but in most cases, this effect will have
to be minimized and will be covered in a later section.