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A very small normal-mode helical antenna (NMHA) has been developed for sensor antennas of the tire pressure monitoring system (TPMS) and tag antennas of the radio frequency identification (RFID), because of the usefulness in metal proximity. In order to achieve an actual antenna applicable to radio units, an impedance matching structure was necessary. A simple tap structure was developed in the works...
Very small normal-mode helical antennas (NMHA) can achieve a high antenna gain in the metal proximity use. So, the NMHAs were developing to use for the RFID (Radio Frequency Identification) tags and the TPMS (Tire Pressure Monitoring System) sensor antenna placed in a tire. In order to achieve impedance matching to the radio unit, a tap feed structure is inevitable. In this paper, the usefulness of...
A very small NMHA having the size of 0.014 wavelength is developed for TPMS. The novel simple impedance matching structure is developed. As a result, antenna gain of -6.75 dBd is ensured in the case of the antenna mounted on a wheel.
Design methods of the simple tap feed structures are clarified. It is shown that this. Tap feed can match very small input resistance of 1.2 Omega to 50 Omega coaxial cable. And through the designed example, achievement of high gain of 1.08 dBd in the low profile normal mode helical antenna is shown in the case of the metal proximity use.
In this paper, the design concept of a rectangular normal mode helical antenna is explained. And calculated and measured antenna input impedance and gain are shown in the metal proximity condition. High antenna gain of 2.06dBd is ensured. Next, the antenna structure capable of matching to an IC chip is shown. By employing this antenna, the metal proximity use tag is fabricated. Communication distance...
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...
A 0.035 wavelength very small normal mode helical antenna is designed to achieve high antenna efficiency. Antenna gain of -3.72dBd is achieved. When this antenna is attached on a metal plate, antenna gain is increased to -0.4dBd. Communication distances of current RFID tags and NMHA tags are measured. In the case of NMHA tags, communication distances comparable to current RFID tags are ensured.
Extremely small normal mode helical antennas (NMHA) for RFID tags were developed. By introducing folded structures, antenna efficiencies of -5 dB and -1.5 dB were achieved in antenna sizes of 0.025 wavelength and 0.05 wavelength, respectively. However, antenna input resistances were very low such as 5 ~ 8 Omega. Impedance matching structures were requested. In this paper, novel impedance matching...
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