Optimal position of an emitter in a wavelength-scale parabolic reflector.

Abstract

We investigate the optimum emitter position within reflecting parabolic antennas whose size is comparable to the emission wavelength. Using finite-element modeling we calculate the dependence of the amount of power directed into a 20° half-angle cone on the emitter's position and compare with results obtained using geometrical optics. The spatially varying density of states within the wavelength-scale reflector is mapped and its impact discussed. In addition, it is demonstrated that changing the characteristic size of the reflector within the range from 0.5 to 1.5 times the emission wavelength has a strong bearing on the optimum emitter position, a position that does not in general coincide with the parabola's focus. We calculate that the optimal antenna size and emitter position allow for the maximum directed power to exceed that obtained in the geometrical optics regime.