A wide band flat spiral antenna with planar unbalanced feed

A high gain 3-arm spiral antenna with planar unbalanced feed is proposed. It is shown that the traditional characteristic of spiral antenna apply to this type of spiral antenna. A very wide band frequency range and circularly polarization are achieved. Through numerous numerical simulation, it was determined that the radiation efficiency of the antenna can be improved significantly once the line width of the tree arms is tapered down as the arms approach to the center of the spiral. The dielectric substrate on which the antenna is printed as also the concept of end loading have big influence on the axial ratio parameter of the antenna. Very good agreement between simulation and measurement was achieved, showing about f: 8f bandwidth, 8dBi gain.