Effects of inter-element spacing on mutual coupling and resonant properties in reflectarray unit cell design

Effects of inter-element spacing on reflectarray unit cell design are studied in this paper. Reflectarray unit cells were commonly analyzed using a waveguide approach which assumed a fixed separation between identical elements in an infinite array. However, in practice, a reflectarray element can be surrounded by non-identical elements with variable distances. It is shown in this paper that the resonant frequency and reflection phase of the reflectarray element noticeably change with respect to different element spacing. A reflectarray unit cell is designed at 2.056 GHz. By changing the distance between the reflectarray elements from 0.33 to 0.68 λ₀ in E plane and 0.33 to 0.78 λ₀ in H plane, the resonant frequency is increased from 1.99 to 2.07 GHz (representing a 4% change) and the reflection phase is shifted by 200°. To prove the concept, two 3 × 3 subarrays with different inter-element spacing are fabricated. The measurement results closely agree with simulated responses. The knowledge gained in this work can make the design of reflectarray antenna more accurate.