Development of electrically small antenna with impedance matching circuit for 2.4GHz band sensor node

For the sensing or short rang wireless telecommunication devices such as vital sensor, security sensor and RF-ID system, integrating entire transceivers on a single chip is the vision for future systems [1]. However, antennas are considered to be the largest components of wireless systems, so that, it is necessary to miniaturize antennas [2]. There are a lot of researches of an electrically small antenna (ESA), i.e., the antenna whose dimension is much smaller than onewavelength, in order to reduce the antenna size [3]. However, it is widely known that in order to realize the miniaturized antenna, we must simultaneously fabricate a broadband impedance matching circuit, which compensates the narrow bandwidth peculiar to the small antenna with low radiation conductance. Also, the small antenna is sensitive to the conductance of the conductor because of its low radiation conductance, and the decrease of the radiation efficiency often makes serious problem. In our previous works, we designed the slot dipole type ESA with impedance matching circuit [4]. In this paper, we designed and fabricated ESAs with impedance matching circuit on the PCB (patterned circuit board, FR4), and mount the sensor node system, which is composed of 8-bit custom micro computer, sensors, RF front end and I/O port.