A Compact 4×4 Butler Matrix with Improved Crossover for Wireless LAN Applications

This work miniaturizes a 4×4 Butler matrix while preserving operational bandwidth, applicable to other order matrix and frequency ranges. By redesigning the crossover using a two-layer microstrip configuration without ground plane perturbation still shows promising results over 1.8 to 3 GHz while occupying just 10% area of a traditional crossover. Modifying the phase-shifting unit and 3 dB branch-line hybrids reduces size without compromising bandwidth. The final prototype 20% area of a traditional matrix. Measured results show return loss below 12 dB, amplitude imbalance within ±1 dB, and phase imbalance within ±100 over 2.2 to 2.6 GHz, ideal for WLAN applications.