High gain design of a very small normal mode helical antenna for RFID tags

Recently RFID tags of 900 MHz band are interested in many commercial fields. Tags are requested to be used on liquid bottles, medicine bottles and metallic plates. So, antennas are requested to be made very small and to have properties capable of use in metal proximity. In this paper, important design subjects to achieve very small antennas are summarized and technical solutions are explained first of all. Following this summary, the normal mode helical antenna (NMHA) is selected as a promising antenna that is suitable for achieving high gain in very small size and metal proximity use. Next, useful design data of NMHA to achieve high gain and metal proximity are shown. And an example of achieving a low profile NMHA is shown. In order to ensure realization, measured results of a fabricated antenna is shown. Moreover, the fabricated antenna is applied to the commercial IC chip. Communication distances are compared with that of the commercial tags.