Systematic Design and Simulation of a Miniaturized Conical Log-Spiral Antenna

This paper presents a systematic method to design an electrically-small conical log-spiral antenna (CSA). The design is based on a thin flexible printed dielectric substrate to form the cone surface, and then a resistor is added between the spiral arms at the larger diameter end of the antenna. To demonstrate the proposed approach, a 2-arm CSA is designed and simulated. The minimum operating frequency of the CSA is reduced from 1.02 GHz to 0.8 GHz. A microstrip balun is designed to differentially excite the CSA. The final antenna has a fractional impedance bandwidth of 121% (0.8-3.27GHz) with return loss better than 10 dB. The axial ratio of the antenna is also assessed to show its circularly polarized performance within the operating bandwidth.