Frequency optimization of parasitic superdirective two element arrays

Results with driven and superdirective two element copper arrays which demonstrate how frequency optimization affects the phase difference between the elements´ currents are presented. The current phase differences resulting after parasitic superdirective array frequency optimization to the theoretical phase differences required for driven superdirectivity and to phase differences computationally determined to be optimal for particular driven superdirective arrays are compared. Comparisons are performed for both endfire directions with the parasitic element used as either a reflector or a director. The results illustrate that frequency shifting and optimization of the parasitic array changes the inter-element current phase difference to one closer to the theoretical and computational phase differences required for driven super directivity. While this phase difference is set in the driven superdirective array by varying the element excitations for each physical separation, in the parasitic array this phase difference can only be influenced by changing the element spacing or the array frequency. At each physical separation there are two optimal parasitic array frequencies which create either +/- the driven superdirective current phase difference. One frequency utilizes the parasitic element as a reflector while the other causes it to act as a director. The technique of frequency shifting a superdirective parasitic array to optimize gain is not limited to the electrically small superdirective parasitic arrays this effect was first noted in, but in fact seems to hold true for parasitic arrays in general as shown in the monopole example.