Enhanced Phase Coherence in Series‐Fed Patch Array Antenna: A Design Method for Uniform Element Spacing With Low Sidelobe Levels

ABSTRACT Microstrip series‐fed patch array antenna (SFPA) is increasingly prominent in millimeter‐wave radar systems. Especially, SFPA with tapered amplitude using Dolph–Chebyshev, Taylor, and Binomial distribution has been developed to reduce a sidelobe level (SLL), which is critical to radar resolution. Even though reported designs of SFPA have achieved notable reductions in SLLs, the patch element and inter‐element spacing optimized by simulation over the entire array design can't guarantee perfect in‐phase radiation. Consequently, for nonuniform SFPA designs, achieving precise in‐phase radiation necessitates a theoretical approach and a thorough phase analysis of each element. In this article, we present a noniterative design method to ensure in‐phase feeding to each patch element by accurately compensating for the phase difference encountered in nonuniform SFPA. This approach begins with designing the electrical length of each patch element to be equal to 35 GHz. Subsequently, delay lines are then designed to provide in‐phase feeding across the array while maintaining uniform spacing between elements. Consequently, we fabricated three 8‐element SFPAs operating at 35 GHz and compared their performance, and the proposed design shows an SLL of –20.7 dB with a radiation angle of 1 . 5 ∘ $1.{5}^{\circ }$.