Some techniques for avoiding dips of antenna radiation efficiency on improved Wheeler method

When the efficiency of a monopole is measured by determining the radiation efficiency of a small antenna based on a waveguide and a movable short, there are dips at certain frequencies. In this paper, a transmission line model considering the loss in the movable short is introduced and the efficiency dip phenomena are explained. A method for avoiding the dip is presented. When two movable shorts on the left and right inserted into the waveguide are moved, an efficiency dip occurs at the resonant frequency of the cavity. Therefore, the movable range of the two movable shorts that will avoid the efficiency dip is investigated. When one of the movable shorts is fixed at an arbitrary location, there is a dip in the radiation efficiency at a specific frequency. Therefore, it is confirmed that the dip can be avoided by limiting the range of the fixed location of the movable short. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(1): 35–44, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20323