Electromagnetic model of a near-field cable-free impedance and gain measurement technique for electrically small antennas

In this paper, a novel near-field cable-free impedance and gain measurement technique for electrically small antennas is proposed. In this technique, with the electrically small antenna placed in the near-field region of the probe, the properties of this antenna are extracted by measuring the signal scattered by it when it is loaded in turn with three known loads. The determination of the antenna impedance and gain is formulated by using the spherical wave expansion technique. The advantages of this measurement technique are summarized as follows. First, the limited dynamic range problem is avoided by the measurement close to the probe. As a result of this, the effect of noise is reduced and the measurement accuracy is improved significantly. Second, only a compact anechoic environment is required, which is easy to build. The expense of this technique is the increased complexity of the model.