Resonant properties of an impedance monopole located on a perfectly conducting rectangular screen

Subject and Purpose. A resonant monopole of an electrical length 0.2 £ l / l £ 0.3 mounted on an infinite, perfectly conducting plane or on a rectangular, perfectly conducting screen is considered. The objective is to determine how the radiation resistance, surface impedance, and input impedance depend on the length and thickness of the resonant monopole and how the screen size affects the resonant characteristics and directive gain of the impedance monopole.

Methods and methodology. A three-dimensional vector problem of the field diffraction of an impedance monopole mounted on a perfectly conducting rectangular screen is solved using the method of uniform geometrical theory of diffraction and adopting asymptotic expressions of the diffracted fields and electric currents of a thin impedance dipole located in the free space.

Results. Taking into account diffraction effects at the edges of the square screen, the resonant values of the surface impedance of the monopoles and the corresponding radiation resistance and directive gain have been calculated subject to the condition that the electric field amplitude is at its maximum. It has been found that as the screen size exceeds the two wavelengths, the edge phenomena have little effect on the monopole resonant characteristics. The radiation resistance reaches its maximum when the side of the square screen is as long as L / l = 0.9…0.95. The first maximum of the directive gain occurs at L / l = 1.2…1.3. The obtained results have been verified with the aid of the computational electromagnetics software FEKO.

Conclusion. A three-dimensional vector diffraction problem has been solved for an impedance monopole mounted on an ideally conducting, rectangular screen. Algorithms and computational programs have been developed to determine resonant characteristics and radiation patterns of the radiating system. By choosing an optimum screen size it is possible to increase the directive gain of an impedance monopole of the length l = 0,2l by 24% and the radiation resistance by 38% compared to the infinite screen.