Extremely Small Antennas for RFID Tags

Recently, UHF RFID tags are planned to commercialize in many countries. Requests for smaller size antennas are becoming strong. Promising candidates for these requests are meander line antennas (MLA) and normal mode helical antennas (NMHA). In this paper, extremely small MLA and NMHA are developed. As for MLA, design data for 0.02 to 0.05 wavelength antennas are shown. By loading high r materials, possibilities of achieving antenna efficiencies greater than -5 dB are shown. Moreover, a convenient feed structure to achieve excellent impedance matching is proposed. As for NMHA, design data for 0.025 to 0.1 wavelength antennas are shown. And achievements of antenna efficiencies greater than -5 dB are shown. Moreover, a convenient feed structure to achieve excellent impedance matching is proposed. Finally, very important measurement method to measure radiation resistance and ohmic resistance are shown. Through this measurement, extremely small antenna behaviors become very clear