What are the Steps for High Gain RFID Antennas Design

When designing rfid antennas, it is not only necessary to consider the actual application scenarios, but also to design an antenna that matches the chip within the specified size range according to specific application requirements. Then in the process of designing the antenna, we must focus on solving the problem of conjugate matching between the input impedance of the antenna and the chip in the working frequency band under the specified size range and working environment conditions. In addition to antenna impedance matching design, we must also pay attention to parameters such as antenna radiation efficiency, polarization direction, and radiation pattern.
 

What are the steps for rfid antenna design
According to the design requirements (tag size, operating frequency band, matching chip, application conditions, etc. are proposed by the requirements), determine the design plan and target parameters, establish the antenna model, and perform simulation calculations on the antenna model. The design model is then adjusted based on the simulation calculation results to achieve the expected target parameters. When designing an antenna, usually various material parameters and structural distribution are determined, usually based on certain conditions. However, RFID tags have a wide range of applications. If the dielectric constant of common materials cannot be determined, the input impedance and other parameters of the antenna in this environment become unknown, which requires testing to determine its parameters.
 

1. Equivalent measurement of tag antenna

From the general design method of tag antenna, it can be seen that the key to design is testing. RFID antennas are divided into high frequency and ultra-high frequency. High-frequency antennas can usually ignore the dielectric effect, and their inductance and distributed capacitance can be measured directly through a bridge or impedance analyzer. Accurate measurement of UHF antennas is difficult to achieve and is usually achieved by equivalent measurement. Here are two measurement methods suitable for UHF RFID antenna design:
 

Resonance method to measure equivalent dielectric constant
The input impedance of UHF tag antenna is sensitive to materials. When attached to different materials, the amount of impedance change usually varies greatly. The equivalent dielectric constant refers to equating the composite material into a homogeneous material, and equating the comprehensive influence of the composite material on the antenna into the influence of a homogeneous material.

From the input impedance curve, you can understand the frequency band around which the real part of the antenna input impedance reaches the maximum and minimum values. The corresponding maximum and minimum values are the resonant frequency band of the antenna.

Then perform simulation calculations according to the size of the composite board. When the dielectric constant value of the composite board is calculated, the maximum real part value of the antenna input impedance simulation calculation can be obtained at the same time. Now that the equivalent dielectric constant of the composite board has been determined, the tag antenna can be designed according to normal design methods.
 

Application of scale model technology and proportional measurement method
Scale model technology refers to reducing (or enlarging) the antenna according to a certain scale ratio under certain conditions, and its characteristic parameters also change as a function of this ratio.

Scaled model technology usually makes a model suitable for testing for the convenience of testing for equivalent testing. The design and measurement of RFID tag antenna can also directly use scaled model technology for equivalent measurement. The ratio measurement algorithm can directly determine the design goals in complex environments. It is faster and reduces the workload than the equivalent dielectric constant measurement algorithm. This method has higher practicability in actual engineering design.
 

2.Determination of tag antenna design frequency band

UHF RFID has different frequency band standards in each country. Therefore, when designing a tag antenna, you must first determine the design frequency band according to the requirements. The antenna equivalent measurement method is used to design the antenna, and the antenna design frequency band is multiplied by the proportional coefficient K.
 

The formula is as follows:

Fmin=Fmin standard×K=minimum frequency band

Fmax=Fmax standard×K=maximum frequency band
 

As long as the characteristic parameters of the antenna in this frequency band reach the target value, it can be achieved. Applying the antenna equivalent measurement algorithm for antenna design can save a lot of simulation calculation work, especially clarifying the frequency band under simple conditions (pure antenna), which will simplify the originally complex calculations.
 

3. Design of dynamic impedance matching

The input resistance of the chip changes with frequency. When the chip is bound to the antenna, the distributed capacitance will also be increased, and there is still a certain difference between the actual input impedance of the chip and the nominal value. In order to enable the tag to work stably and meet the impedance matching within a wider frequency band, the dynamic change of the input impedance of the chip is usually considered when designing the tag antenna and a dynamic impedance matching design is performed.
 

The design steps for rfid antennas are basically fixed. Even for RFID antennas used in complex media environments, as long as you master the appropriate design scheme, the originally complex work can become simpler. At the same time, the design goals, cycle, Costs will be more controllable and transparent.