Research Of UHF RFID Tag Antenna

Radio frequency identification(RFID) technology has been widely used in many fields. A typical RFID system consists of tag, reader and computer background. Tag’s technological is the most worth to develop. A RFID tag is composed of two parts, chip and antenna. The antenna can not be ignored, and because of its complexity, importance and diversity, it has become the focus of domestic and foreign scholars’researches.This paper focuses on the UHF tag antenna, which has the fastest development and the widest prospects. And the paper puts the target on dipole antenna, which has the best comprehensive performance. In the research of tag dipole antenna, miniaturization technology and impedance matching technology are the keys.For miniaturization, bending is the most simple and common method. At present, most scholars design antenna based on the law of simulation.This paper uses a design method of MLA based on a formula, which establishes the relationship between antenna dimensions and resonant frequency. This method can design the MLA at specific working frequency quickly and easily. Meanwhile the paper designs three MLAs(bending number from1to3) resonating at915MHz by using this formula method.For impedance matching, this paper studies and compares the impedance matching network used currently. And a reactance component is introduced in the formula of miniaturization to adjust MLA’s impedance. The improved formula can calculate the structural parameter of the MLA matching to the target chip accurately. And ML As matching to Kunrui chip at915MHz are designed on rigid and flexible substrate respectively in this method. Finally, based on the disadvantage of MLA and the comparing of the impedance matching networks, two capacitive loads are added at the end of MLA to adjust the impendence. For saving material, holes are digged on the loads. Simulation by HFSS shows that, comparing with the regular MLA, the proposed antenna’s impedance enhances from10-12J to23+150j, and the maximum gain enhances from1.31dB to1.67dB, with a read range of9.9m. Meanwhile the return loss at915MHz is-34dB, with a wide-10dB bandwidth of860～985MHz. And comparing with the simple MLA with capacitive loads, the improved antenna has a material saving of25.6%. At last, his paper proves the feasibility of the design methods by testing physical properties of above antennas.