Study on the Parasitic Effects of Yagi Antenna Based on Sub-Structure Characteristic Mode Theory

In this paper, an improved five-element Yagi antenna with parasitic elements is designed based on the substructure characteristic mode theory (SSCMT). The antenna is composed of an active dipole, a reflector and three directors. The parasitic elements are placed near the directors. The impact of parasitic elements at different positions on the radiation performance is discussed. Parasitism of different directors can cause changes in the modal current distribution, leading to changes in modal far-field. A parasitic scheme is proposed based on the maximization of the modal current distribution of the end directors, which can maintain high gain and good directivity. The radiation performance of the proposed antenna is verified by numerical simulation. The antenna increases the bandwidth by 33MHz and the peak gain in the operating bandwidth (2.38- 2.62GHz) by 0.63dBi.