Reduced Sidelobe Four-Beam $N$-Element Antenna Arrays Fed by $4times N$ Butler Matrices

The paper presents reduced sidelobe four-beam antennas fed by modified Butler matrices. The goal is to show the limitations in sidelobe level reduction imposed by the use of lossless feeding networks. Novel concepts of six- and ten-element antenna arrays are proposed. Sidelobe level reduction has been achieved by increasing the number of radiating elements and by applying unequal split power dividers or directional couplers. The minimum achievable sidelobe level have been found for 4-, 6-, 8-, and 10-element antenna arrays fed by lossless networks and compared with the one for antennas fed by lossy networks in which there is no constraints on radiating elements' amplitude distribution. Measured radiation patterns of three different four-beam antennas have been shown to validate the presented analyses.