DEPENDENCE OF THE EFFICIENCY-BANDWIDTH PRODUCT OF SMALL DIELECTRIC LOADED ANTENNAS ON THE PERMITTIVITY Ichirou IDA 1 *, Jin SATO 1 , Takatoshi SEKIZAWA 1 , Hiroyuki YOSHIMURA 2 , and Koichi ITO 2 1 Graduate School of Science and Technology, Chiba University 2 Faculty of Engineering, Chiba University 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan Tel: +81-43-290-3326, Fax: +81-43-290-3327 E-mail: ito@cute.te.chiba-u.ac.jp I. Introduction There are several criteria for antenna evaluation. Particularly, the authors have studied on the efficiency-bandwidth product (EB) for small dielectric loaded antennas (DLAs)[1]-[3]. In general, the EB takes almost the same value among antennas having the same electrical volume. The performance of the antenna is therefore considered to be enhanced when its EB has been increased keeping the same electrical volume as before. To evaluate the EB, its dependence on the permittivity of the DLAs is of particular interest. In [2], the existence of the peak value in the Wheeler’s radiation power factor (PF, i.e. the EB) [1] was analytically predicted when the permittivity of the dielectric loading was changed. Although the DLA in [2] was an infinitesimal electric dipole located at the center of a dielectric sphere, other shapes for the dielectric loading are also of interest to investigate the permittivity dependence of the EB. The EB is simple in its expression and only needs a radiation resistance and an input reactance of an antenna. This feature of the EB is very advantageous because one can measure the radiation resistance of the small antennas with a sufficient precision by using the Wheeler cap method [4]-[7]. The experimental considerations on the EB have, however, rarely been reported. In this paper, the EBs of small cylindrical dielectric loaded monopole antennas (DLMAs) are measured and dependence of the EB on the permittivity of the dielectric loading is investigated. For the measurement, small radiation resistances of the DLMAs are precisely measured on the basis of the Wheeler cap method. Finally, permittivity dependence of the EB is discussed from the viewpoints of the measured results as well as a mathematical reasoning. II. Measurement of the EB The EB is expressed as the following equation where R r , R loss and X are the radiation resistance, conductor loss and input reactance of an antenna, respectively. From (1), one needs only a ratio of the radiation resistance to the input reactance of the antenna in order to obtain the EB. This simple expression is useful for both experiment and calculation. Fig. 1 Dielectric loaded monopole antenna (DLMA) ) ( 1 1 X R R R X R R R EB r loss r loss r r = + ⋅ + = φ 1.3 dielectric loading (ε r = 2.30, 3.16, 4.76, 6.84, 12.0) Unit : mm center monopole ground plane (900 x 1000 mm 2 ) φ 9.6 6.0 PROCEEDINGS OF ISAP2000, FUKUOKA, JAPAN