Dual Polarization Omnidirectional RFID Antenna Design for Logistics Industry

0 Preface

At present, with the wide application of radio frequency identification (RFID) in identification, banking, traffic cards, etc., it has attracted more and more attention from various fields of society. In addition, as the country mentions the construction of "Internet of Things" to the status of strategic industry, the application of RFID in logistics and warehousing has been paid more and more attention by various logistics companies. The application process of RFID in logistics and warehousing includes cargo tracking in the logistics process, automatic collection of information, warehouse management applications, port applications, postal parcels, express delivery, etc. For example, a lot of research has been done on RFID Antennas used in fields such as identification in the literature. In the Logistics industry, the application of RFID is different from the application of RFID in identification. It needs to be able to transmit and receive signals within a long distance and in different directions, which requires the antennas used in the logistics industry to have comprehensive tropism. At the same time, since the main transmitting and receiving system of the logistics identification system cannot be made very large, its antenna polarization direction may not be able to be circularly polarized. This requires that the RFID antenna be made into a dual-polarized antenna so that it can Any direction enables the main receiving system to receive the signal of the RFID tag board.

1 Design of circular patch antenna with dual feed points

At present, the research on circular patch antennas mainly tends to be miniaturized, and the research on dual polarization is basically not involved. The antenna of the circular patch with dual feed points is to make the circular patch dual-polarized.

1.1 Dimensions of dual feed point fixed patch antenna

The antenna of the circular patch with dual feed points is divided into two parts: the feed part and the circular patch part. The feeder part is a feeder lead out from a feeder, and then branched on the feeder to form two feeder lines, which are respectively fed to the two perpendicularly intersecting diameters of the circular patch antenna, and the line lengths of the two branch feeder lines differ by λ/ 4. In order to make the antenna impedance matching value 50 Ω, a tuning matching branch is set at the feed port, as shown in Figure 1. By adjusting the lengths of L2 and L1, the impedance of the antenna can be adjusted to 50 Ω. This form of matching circuit is easy to manufacture and low in cost.

1.2 Simulation results of circular patch antenna with dual feed points

The simulation results of the circular patch antenna with dual feed points are shown in Figure 3 and Figure 4. Figure 3 shows its standing wave ratio, and Figure 4 is the radiation pattern of its E plane. It can be seen that the standing wave ratio is less than 2 in the range of 2.8-2.92 GHz. It can be seen from Fig. 3 and Fig. 4 that the initial design purpose has been achieved.

2 Broadband deformation inverted L antenna design

2.1 Dimensions of broadband deformable inverted L antenna

The inverted L antenna is composed of a horizontal element and a vertical element, and has horizontal polarization and vertical polarization performance, and its length sum is approximately λ/4, so it has low proFile characteristics. But its frequency band is relatively narrow, typically only one percent of the center frequency. The bandwidth of the deformed inverted L antenna designed in this paper will be greatly widened. The structural diagram of the inverted L antenna is shown in Figure 5.

The dielectric board used is FR4 board, the dielectric constant ε=4.4, the thickness of the dielectric board is 1.5 mm, and the line width W=1 mm.

2.2 Simulation results of deformed inverted L antenna

The simulation results of the deformed inverted L antenna are shown in Figure 6 and Figure 7. Figure 6 shows its standing wave ratio, and Figure 7 shows its E-plane direction diagram. It can be seen from Figure 6 that the standing wave ratio of 2.37-3.29 GHz is less than 2, and the bandwidth is 32.3%, which is much higher than the bandwidth of ordinary inverted L antennas. It can be seen that the design requirements have been met.

3 Conclusion

This paper designs and simulates two dual-polarized omnidirectional antennas with a center frequency of 2.85 GHz. The simulation results of the two antennas meet the design requirements. Among them, the dual-feed point circular patch antenna is suitable for the collection and tracking of cargo information of irregular packages. The dielectric board used in this design is a soft dielectric material with a thickness of 0.2 mm. The bandwidth of the deformed inverted L antenna reaches 32.3%, which can be used for cargo information tracking when broadband is required.