Original Ka-band fractional spiral antennas

The original fractional $-shape spiral antenna being fed from the Ka-band metal waveguide is proposed. The impedance bandwidth of such an antenna is 6.7GHz. Herewith, the axial ration does not exceed 3dB level within the limits of 34.2 - 37 GHz. The radiation pattern of such an antenna is similar to the monopole antenna with zero-radiation intensity in the antenna axis and with an elevation angle of peak directivity equal to about θ=20°. It is important, that the radiation pattern shape does not undergo any visible deformations through the operational frequency band. The use of near-field technology allows for explaining the basic reasons of the axial ratio changing through the antenna bandwidth. The proposed antenna seems to be very attractive for various practical applications in the millimeter range.