Miniaturization Design for 8 × 8 Butler Matrix Based on Back-to-Back Bilayer Microstrip

Figure 3

The upper circuit structure diagram of the three-branch line directional coupler, in which 𝑊₁=0.4mm, 𝑊₂=3.5mm, 𝑊₃=3.5mm, 𝐿₁=16.5mm, and 𝐿₂=11.3mm.