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.