Composite Excitation for a Two-Arm Spiral Antenna

This paper describes novel movement of the direction of the maximum radiation from a two-arm spiral antenna. Antenna feed points F1 and F2 are excited with V1 volts and V2 volts, respectively, where the phase of V1 is 0 degrees and the phase of V2 is 180 degrees plus a deviation angle of α
_dev
degrees. This is treated as a superimposition of the excitation from a pair of out-of-phase voltage sources (OutPVSs) and the excitation from a pair of in-phase voltage sources (InPVSs). The OutPVSs generate a circularly polarized (CP) beam in the broadside direction, while the InPVSs generate a CP conical beam around the vertical center axis normal to the antenna plane. It is found that a change in voltage V2 relative to voltage V1 moves the direction of the CP maximum radiation in a specific direction. The 3-D radiation is presented, as well as other antenna characteristics.