Abstract
Measuring loop antennas used in the frequency band below 30 MHz have been generally calibrated with the standard field method, where a standard loop antenna generates a well-defined magnetic field at an antenna under calibration. However, it is very difficult to evaluate the strength of the generated field with great accuracy. To cope with this problem, the present paper newly develops a calculable loop antenna consisting of a loop element and a 180 degrees hybrid junction. This antenna can be used as a standard transmit antenna as well as a standard receive antenna. Thus, it is applicable to other calibration methods, such as standard antenna method and three-antenna method, which can improve the accuracy of the antenna calibration. As an example, a calibration system is proposed for the standard field method, where the proposed calculable antenna is used as a standard transmit antenna. The strength of the generated field is rigorously evaluated by measurements of the reflection coefficient and the supplied power at the transmit antenna input. From experimental measurements using the proposed calibration system, it is ensured that the proposed system can provide antenna calibration with accuracy within 0.3 dB in almost all the frequency range from 1 to 30 MHz
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