Analysis and design of miniaturized ultra-wideband conical log spiral antennas

A well performed miniaturized ultra-wideband conical log spiral antenna is designed and fabricated in this paper. The conical log spiral antenna which is able to cover S to X band is designed and simulated based on the antenna requirement and commercial software HFSS. A microstrip balun (balanced-to-unbalanced transformer) is also designed to match the designed antenna and the coaxial line. Then, the balun is added to the conical spiral antenna, and the whole model is being simulated and optimized. The axial ratio and the VSWR of the low frequency are greatly improved by introducing resistance and absorbing material. The conical log spiral antenna is then fabricated and measured. Measured results are in reasonable agreement with the simulated results, which show that the antenna has a wide beamwidth of about 100°, an axial ratio of less than 3dB and a VSWR of less than 2.0 over an ultrawideband of 6:1.