Electrically small structural antenna design for small UAV based on characteristics modes

A systematic approach in developing a 4-port structural antenna system on a Small Unmanned Aerial Vehicle (SUAV) is presented. The largest dimension of the SUAV is 0.67 wavelength of the operating frequency. Using Characteristic Mode (CM) Analysis, two significant CMs with good radiation efficiency are identified. The radiation patterns of these two CMs can be synthesized by combining the individual element gain patterns with specific amplitude and phase settings (either in-phase or out-of-phase). In addition, the radiation pattern may be gradually steered from one CM to another by progressively changing the phase settings. A 1:5 scaled model of the SUAV is fabricated and the respective CMs are excited; the gain patterns are measured in an anechoic chamber. The resulting gain patterns can be combined either via a suitable RF combiner or digitally beamformed. In both cases, the results agree well. This method may be used to provide steering, albeit limited, of the gain pattern of an electrically small structural antenna.