There are two versions of the microstrip line slot array antenna: resonant array and nonresonant array according to its termination. Because microstrip loss is much larger than waveguide loss, a design method for the waveguide array is not applicable to the microstrip array. This paper proposes a new design method that utilizes nonlinear optimization and reduces the total loss; it is compared with a conventional design method. Two 2‐array antennas with 64 elements were manufactured with new and old design methods. The antenna designed by a new method showed predicted properties.

Microstrip line slot‐array antennas consisting of slots placed on the ground plane on both sides of the microstrip line may be classified into resonant‐ and nonresonant‐types. Both types exhibit a beamtilt—namely, the main beam direction shifts as the operating frequency is changed away from the center frequency. This beam‐tilt causes the gain in the specified direction to degrade rapidly, which is a serious drawback in a system for receiving a signal with a given bandwidth from a fixed direction. To overcome this deficiency, a method available for waveguide slot‐array antennas is used and a design procedure is developed. Further, it is shown experimentally that beam‐tilt is almost nonexistent over a relatively broad frequency range and constant gain is obtained. The gain is higher than that of conventional antennas. Sidelobes are suppressed, especially for nonresonant arrays. The usefulness of the microstrip line slot‐array antenna with a reduced beam‐tilt is demonstrated.

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