Low Profile Small Normal Mode Helical Antenna

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. Recently, very small normal mode helical antennas (NMHA) of 0.035 wavelengths were developed. They could be used near metallic plates and liquid bottles. However, because the cross section at shape of the NMHA was circle, the developed NMHA was not low profile. For convenient use, the low profile antenna shape is requested. In this paper, the cross sectional shape of the small NMHA is changed to a rectangular. In this case, it becomes suspicious if comparable electrical characteristics to the developed 0.035 wavelength antenna can be achievable in the similar size. First of all, electrical and structural characteristics of the developed circular NMHA were summarized. Next, design graphs of electrical characteristics in the rectangular NMHA are pursued. Finally, in order to ensure the realization of simulated results, an antenna is fabricated and experimental studies are carried out. The antenna gain of -2.87 dBd is ensured. Moreover, in the case of the metal plate proximate use, the antenna gain of 0.12 dBd is ensured.