An electrically invisible dipole loaded with a variable reactor and its applications for a reconfigurable antenna

This paper shows that the integral of the current flowing on a parasitic dipole can be made to vanish by supplying a reactance with an appropriate value. When a reactor is placed at the center of a half-wave dipole with a thickness of 0.02 wavelength, the reactance value making the integral of the current vanish is about +450 Ω. The state in which the integral of the current is zero is not affected by other elements and minimizes the electrical influence on other elements. Hence, this state is considered electrically invisible. A reconfigurable (structurally variable) ESPAR antenna is proposed in which a variable reactance is placed on a parasitic dipole and the combination is adequately made electrically invisible. A method of calculation is proposed in which the admittance of the array configuration without a specific dipole element is obtained from the admittance in the presence of such an element by making it electrically invisible. Further, by this calculation method, the behavior of the admittance of an array with symmetrically placed elements is obtained. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(3): 21–35, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20262