Analysis And Design Of UHF RFID Tag Antenna For Metallic Surface

Radio frequency identification (RFID) system has a wide range of application in future, and many countries paid lots of attention on it. As a result of its advantage, UHF RFID system now is the international hot spot. The RFID antenna in UHF frequency band is the key component of RFID tag, but the antenna that design on free space can be influenced greatly by metallic surface, which will cause the instability of the system. Some work on the thin (easy to be conformal with object) UHF RFID tag antenna for metallic surface is done and some kinds of antennas that can be used on metallic surface are designed in this paper.The performances of UHF RFID system largely depend on its reading range, and the reading range is greatly influenced by the gain and impedance matching of antenna, the paper makes some success at these two points, the main work and innovation points are as below:1. A microstrip patch antenna with a feeding line at incison is designed. Its structure is something new, used on a dielectric layer with the thickness of 0.635mm, the peak gain is -4.5dBi, and the Variational range of input impedance is(5～95~+) + j(100～350~+)Ω, it is fed by feeding line. Its structure is simple and the cost is low. The antennas are produced based on the design results and measured. Measurement results and simulation results are basically the same.2. A circular slot antenna fed with CPW is designed. Also its structure is and used on the layer with a dielictric thickness of 0.635mm, the peak gain is -4.7dBi, and the Variational range of input impedance is (8～150~+) + j(80～600~+)Ω, it is designed to be integrated with the chip, so the cost is reduced; it is suitable for mass production. The antenna is produced. Measurement results and simulation results are basically the same.3. The antennas with different kinds of metal environment are simulated and analized. The results can be sorted in three conditions: First, in the condition that there is metal aroud the antenna, if the distance between the antenna and the metal is about even times ofλ/4 (λis the wavelength corresponding to operating frequency), the gain will be enhanced by metal; If the distance is around double times ofλ/4, the gain will be weakened. Second, increasing the length along surface current will contribute to the gain at first, and then the opposite; while increasing the length calibration to surface current will reduce the gain constantly. In these two conditions above, the return loss is little influenced. Third, the antenna is bent along the cylindrical metallic surface. When it is bent along the surface current, the gain will keep reducing; in the opposite condition, the gain will be increased constantly.