Universal Design Method for Traveling Wave Series-Fed Array Antennas

Microstrip traveling-wave series-fed array antennas are popularly utilized for millimeter-wave radars and communication systems due to low loss from a feeding network. However, the design difficulty compared to parallel-fed arrays for in-phase radiation is inevitable due to the loading and mutual coupling effects between the antenna elements connected in one single feeding line. For the in-phase radiation, the distances between antenna units have been tuned, but the tuning process is cumbersome due to the interdependence between the units. This paper introduces a universal and tuning-free design method of microstrip traveling-wave series-fed arrays for in-phase radiation. We designed series-fed patch and comb-line arrays operating at 76.5 GHz based on the proposed method and proved the in-phase radiation with the main beam at the boresight and a sidelobe level near -20dB.