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

A low-cost, compact 8 x 8 Butler matrix based on a novel bilayer microstrip configuration is presented and implemented for 4.3 GHz telecommunication application. A back-to-back placed bilayer microstrip structure has been proposed to avoid using crossover. To expand operational bandwidth of the Butler matrix, a three-branch line directional coupler has been employed as 3 dB/90 degrees bridge, and a kind of improved two-order Schiffman phase shifter has been adopted as fixed phase shifter. For application of indoor wireless communication, a compact broadband 8 x 8 Butler matrix has been designed and fabricated. The measured results show that the return loss of the matrix is lower than -10 dB, the isolation is better than 17 dB, the power distribution error is less than +/-2.0 dB, the phase error is less than +/-15 degrees, and the relative bandwidth is more than 23%.