Four-arm 2nd-mode conical spiral antenna feeding with split tapered coax balun

A novel coaxial line is presented to feed the second mode four-arm conical spiral antenna. Against the conventional 3dB bridge beamformer, the proposed scheme simplifies the design and fabrication, and makes it more flexible in the optimization of the parameters such as the feeding amplititude and phase. The simulated and experimented results are provided which show a bandwidth of 2.25:1 in terms of voltage standing wave ratio better than 2 and radiation pattern beamwidth.