RADIO FREQUENCYRADIO FREQUENCY
IDENTIFICATION AND ITS READERIDENTIFICATION AND ITS READER
Radio-frequency identification (RFID) is an automatic identification
method using radio waves.
RFID is a technology that incorporates the use of electromagnetic or
electrostatic coupling in the radio frequency (RF) portion of the
electromagnetic spectrum to uniquely identify an object, animal, or
RFID is also called dedicated short range communication.
Biometrics (e.g. fingerprint)
Special Characteristics of Radio Communication:
No physical contact
Components of RFIDComponents of RFID
3. Reader antenna.
4. Host and software system.
An RFID tag is a device that can store and transmit data to a reader in
a contact less manner using radio waves.
Each tag contains a unique code that facilitating the identification
process & is known as EPC (Electronic Product Code).
Passive RFID TagsPassive RFID Tags
No on-board power source (for example, a battery)
Uses the power emitted from the reader to energize itself and
transmit its stored data to the reader
Reader always communicates first, followed by the tag.
Smaller than an active tag.
It has a variety of read ranges starting with less than 1 inch to about 10
feet (3 meters approximately).
Cheaper compared to an active or semi-active tag.
Has on-board power source .
No need for reader's emitted power for data transmission
A tag always communicates first, followed by the reader.
High Read Range
transponder - reader
RFID backscatter coupling
RFID inductive coupling
An inductively coupled transponder (tag) comprises of an electronic
data carrying device, usually a single microchip and a large area coil
that functions as an antenna.
The reader's antenna coil generates a strong, high frequency electro-
magnetic field, which penetrates the cross-section of the coil area.
By induction, a voltage is generated in the transponder's antenna coil.
Used in Short range communication (< 1m).
Communication between reader and tag (long range).
Reader sends a signal (energy) to a tag, and the tag responds by
reflecting a part of this energy back to the reader.
A charge device such as a capacitor contained in the tag makes this
The capacitor gets charged as it stores the energy received from the
As the tag responds back, it uses this energy to send the signal back
to the reader. The capacitor discharges in the process.
Linear Polarization (dipole antennas) - the electromagnetic wave
propagates entirely in one plane (Vertical or Horizontal) in the
direction of the signal propagation. This is the best wave propagation
when the tag orientation is known and fixed.
Circular Polarization (helix, patch): This is best to use when tag
orientation is unknown, but you lose at least 3dB when compared to a
linear polarized antenna.
Radiation from the quadrifilar antenna is circularly polarized.
Comprises of two bifilar helical loops oriented in a mutually orthogonal
relation on a common axis.
The terminals of each loop are fed 180° out of phase,
Used in aircrafts, LEO satellites.
Quadrifilar Helix Antenna in RFID
Composed of four helical elements that are fed at each port with equal
amplitude and phased at 0°, 90°, 180°, and 270° respectively.
The helical elements are bottom fed at the ground plane.
Gain of 5.4 dB .
Bandwidth of 900-930 MHz.
Garret I. McKerricher and Jim S. Wight ” Design of a Shaped Beam RFID Reader
Antenna” in IEEE 14th International Symposium on Antenna Technology and Applied
Electromagnetics [ANTEM] and the American Electromagnetics Conference