An experimental investigation into the control of antenna input impedance through cancellation of near field standing energy

It is commonly accepted that efficient, electrically small antennas cannot be built; the general acceptance of this premise comes from analytic work based upon use of the complex Poynting thereom (CPT). In contrast to CPT based results, earlier analytic work has shown that the input reactance of a pair of identical, perpendicularly oriented electrically small electric (TM) or magnetic (TE) dipoles can be canceled if the antennas support circular polarization; these analytic results have been confirmed via finite difference time domain numerical modeling in combination with the time dependent Poynting theorem. We have built and characterized such antennas, using both wire and microstrip dipole elements. In agreement with earlier analytic and numerical work, we find that the input reactance of the antenna can be controlled as a function of the relative phase difference between the two dipoles comprising the antenna. In contrast to the frequency domain predictions, the experimental results confirm the validity of the time domain description of standing energy, or local power. Canceled by controlling the relative phasing between elements, the results show that efficient, electrically small antennas can be built with operating characteristics superior to what has long been thought possible.