Microstrip transmission lines connecting to the millimeter wave radar chip and antenna significantly impacts on the radiation efficiency and bandwidth of the antenna. Here, a wideband non-uniform wavy microstrip line for complex impedance at automotive radar frequency range is proposed. Different to the gradient transmission line, the wavy structure is composed of periodically semi-circular segments. By adjusting the radius of the semi-circular, the surface current varied and concentrated on the semi-circular segments, allowing a wider tunability range of the resonant frequency. The results reveal that the bandwidth of the loaded wavy transmission line antenna improves up to 9.37 GHz, which is 5.81 GHz wider than that of the loaded gradient line. The gain and the half power beam width of the loaded antenna are about 14.69 dB and 9.58°, respectively. The proposed non-uniform microstrip line scheme may open up a route for realizing wideband millimeter wave automotive radar applications.