The sinuous antenna is an interesting candidate for omni polarization applications. Thus, the sinuous antenna is one of the most important popular types, which is used for direction finding in electronic warfare. A sinuous antenna was investigated to achieve fixed axial ratio(AR), low voltage standing wave ratio (VSWR), acceptable gain and low sidelobe levels over a wider frequency band (2-18 GHz). Moreover, the dual senses of circular polarization (right and left hand circular polarization) can be obtained. The sinuous antenna was designed from intersections of two opposite spirals, which can be planar or non-planar. A new design model was proposed based on modulation of periphery of the lower frequency to increase the electrical path of the lower frequency range. This would add some advantages to the original model such as the achievement of a wider operating frequency range (1.43-18 GHz). The same principles were applied in this new model, and the new frequency bandwidth constitutes an improvement to the same original size of the antenna.