Low Sidelobe Design of Microstrip Comb-Line Array Antenna Using Deformed Radiating Elements in the Millimeter-Wave Band

This communication presents a microstrip comb-line array antenna for the low sidelobe level (SLL) in the millimeter wave. As the width of the conventional stub-shaped radiating element becomes wider, not only the longitudinal current but also the transverse current increases; the longitudinal and transverse currents generate the co- and cross-polarized radiation, respectively. To reduce the transverse current flows on the large-width radiating element, the width of the connecting part with the feeding line in the radiating element is narrowed. In addition, the transverse current can be further reduced by adding a notch on the top of the radiating element. These two deformed radiating elements are proposed and used to design 18-element comb-line array antennas according to the array design procedure based on the radiation conductance. The array antennas were designed for the SLL of-20 dB at 79 GHz. The prototypes are fabricated and the antenna performance was measured. From the measurement results, the comb-line antenna composed only of the conventional stub-shaped elements shows the SLL of about-16.58 dB, whereas the array antenna using the proposed elements has the SLL of-19.4 dB. This communication demonstrates the feasibility of the proposed elements for low SLL, through analysis and measurement.