In an RFID system, Antennas play a crucial role in transmitting and receiving RFID signals coming from the RFID readers and RFID tags. An Antenna is a crucial component amongst other RFID components such as an RFID tag, Reader, and the RF subsystem, the software component of an RFID system.
RFID tags and inlays have an inbuilt RFID antenna that receives the RF (Radio Frequency) signal coming from the RFID Reader and uses the signal energy to power up the RFID tag. The RFID tag, in turn, sends the encoded information in the form of an RF signal which is captured by the RFID Reader Antenna. Talking about RFID Reader Antennas, the RFID handheld Readers and RFID Integrated Readers come with in-built antennas while Fixed RFID Readers use external Antennas to transmit and detect RF signals in a business setting, indoors or outdoors.
When choosing an RFID antenna, the most important thing is the antenna gain and the range it offers, apart from the polarization of the antenna, the linear polarization, and the circular polarization.
What is Antenna Gain?
Antenna power gain, Antenna gain or simply gain is the ratio of the radiation intensity in a given direction to the radiation intensity that would be obtained if the power were radiated isotropically. It is basically the amount of power transmitted in the direction of peak radiation compared to an isotropic source with a gain of 0 dBi.
Antenna gain is an important performance indicator that measures how well an antenna transmits radio signals or receives them. It is denoted by the symbol G. Antenna gain is directly proportional to the antenna directivity. The antenna power gain is denoted by Gp and the antenna directive gain is denoted by Gd.
When transmitting RF signals, the antenna gain specifies how well it converts input power into radio waves in a specific direction, and when receiving RF signals, antenna gain specifies how well the antenna converts the radio signal coming from a specific direction into electrical energy.
How to Measure Antenna Gain?
Antenna power gain or Antenna gain is the performance indicator that shows how well the RFID antenna transmits and receives RF signals. Since Antenna gain is a ratio, ideally it shouldn’t have a measuring unit. However, it is measured in decibels over isotropic (dBi). Gain relative to a dipole antenna (dBd) is also used as a metric in broadcast engineering and other industries.
Polarization in an Antenna
While choosing an RFID antenna, it is also important to look at the RFID antenna polarization, which is very important for efficient RFID performance. RFID antennas come in two main polarizations as follows:
1.Linear Polarization RFID Antenna
2. Circular Polarization Antenna Antenna
Linearly polarized antennas transmit and receive RF signals from a single plane, a linear directivity. It means that while installing a linearly polarized antenna, the direction must be carefully aligned to meet the objectives of the RFID application in an RFID system.
Linear polarized Antennas also offer a longer read range as the RF signals travel only in a single direction.
Circularly polarized RFID antennas can transmit and receive RF signals from two planes, in a circular direction which means that it can capture and transmit RF signals very effectively and you don’t have to align it in a specific direction. However, circularly polarized antennas offer a comparatively lesser read range when compared with a linearly polarized antenna for the same power gain rating.
What is the difference between dBi and dBic?
The full form of dBi is decibels over isotropic while the full form of dBic is decibels over isotropic circular. While dBi is used to measure the gain of all kinds of RFID antennas, dBic is used to the gain of an RFID antenna having circular polarization.
How to choose RFID Antennas?
While selecting an RFID antenna, one must consider many factors such as application, environment, and the gain of the RFID Antenna. However, often people ask, which is better, an antenna with high gain or low gain? The answer is not that simple.
High gain RFID Antenna offers a long read-range
As it stands, a higher gain RFID offers a longer read range in contrast to a low gain RFID antenna. However, a higher gain RFID antenna is not always better. In some cases, a low-gain RFID antenna offers better performance as low-gain antennas offer wide coverage, like a wide light beam.
What is a good gain for an antenna?
While selecting an RFID antenna, it is also important to focus on how much the antenna gain rating is. Depending upon the application, it is important to install an RFID antenna with good gain that can accomplish the task of transmitting RF signals and capturing RF signals.
A 9 dBi or 12 dBi RFID antenna is suitable for RFID applications where a long read range is required. These applications include:
1.Intelligent Transportation
2. Warehousing applications
3. Event management
4. Retail operations, etc.
A 3.5 dBi RFID antenna is suitable for RFID applications where a short read range is required. These applications include:
1.Animal tracking
2.Access control
3.Vehicle identification
To conclude, RFID antennas are used to transmit and receive RF signals and while selecting an RFID antenna, antenna gain plays an important role. Antenna gain is measured in dBi and measures how well an antenna converts the RF signal into electrical energy while receiving and how well it converts the electrical energy into an RF signal while transmitting. While selecting an RFID antenna, one must not just consider the antenna gain but also the environment of the application and the specific need of the antenna.
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