Electrically Small Loop Antenna Loaded by a Homogeneous and Isotropic Ferrite Cylinder. Part 2

Abstract

Abstract : Two theoretical approaches are developed to determine the magnetic current distribution on a ferrite cylinder of finite length that is center-driven by an electrically small loop antenna carrying a constant current. The first method makes use of the analogy between the ferrite rod antenna and the conducting cylindrical dipole antenna to derive an integral equation for the magnetic current on an infinitely permeable (mu sub r = infinity) ferrite antenna that corresponds to the integral equation for the electric current on a perfectly conducting electric dipole antenna. In the limit h approaches infinity, this integral equation is shown to agree with that obtained previously in Part 1 for the infinite ferrite rod antenna. Continuing to parallel the treatment of the electric dipole antenna, the integral equation is modified by the introduction of an internal impedance per unit length of the magnetic conductor to account for values of mu sub r that are large but not infinite, and finally an approximate, three-term expression is derived for the current on an 'imperfectly conducting' magnetic conductor. The second, more rigorous theoretical approach obtains two coupled integral equations in terms of the tangential electric field and the tangential electric surface current from independent treatments of the interior (ferrite) and exterior (free space) problems. The coupled equations are then solved numerically by means of the moment method. Finally the results of the two theories are compared with experimental measurements made on eleven different antenna configurations. The agreement is good.