抄録
The efficiency-fractional bandwidth(EB)product has been used as a criterion of the evaluation of small dielectric loaded antennas(DLAs). The EB product seems appropriate to evaluate the goodness of the small antenna, because it is expressed as a simple ratio of radiation resistance to input reactance of such an electrically small antenna. Measurement of input impedance of such an electrically small antenna, however, is difficult by using a network analyzer because one needs to measure the small resistance of the antenna under much of uncertainty like residual systematic or drift errors. In this report, first, several DLAs with almost the same volume are compared with a bare dipole by using the EB product and it is found that some DLAs give enhancement of the EB product over the bare dipole. In addition, it seems that there is an optimum value of dielectric loading with lower permittivity to obtain the highest EB product. Next, to reduce the measurement errors, the antennas are matched to the transmission line with a stub tuner. Then the measured impedance was converted using S-matrix to give the antenna impedance. As a result, we can measure small resistance with small measurement errors.
