A cable-free impedance and gain measurement technique for electrically small antennas

Impedance and gain measurements for electrically small antennas represent a great challenge due to influences of the feeding cable. The leaking current along the cable and scattering effects are two main issues caused by the feed line. In this paper, a novel cable-free antenna impedance and gain measurement technique for electrically small antennas is proposed. The antenna properties are extracted by measuring the signal scattered by the antenna under test (AUT), when it is loaded with three known loads. The technique is based on a rigorous electromagnetic model where the probe and AUT are represented in terms of spherical wave expansions (SWEs), and the propagation is accounted for by a transmission formula. In this paper the measurement results by the proposed technique will be presented for several AUTs, including a standard gain horn antenna, a monopole antenna, and an electrically small loop antenna. A comparison of measurement results by using the proposed method and by using other methods will be presented.