Design and implementation of Butler matrix-based beam-forming networks for low sidelobe level electronically scanned arrays

In this work, the design, fabrication, and testing of low sidelobe level (SLL) Butler matrix-based beamformers is presented. The paper is divided in two parts. The first part deals with the conventional technique of simultaneous excitation of input ports. The second part introduces some novel modified low SLL Butler matrices, as an alternative advantageous design choice. Circuit architecture makes use of asymmetric branch line couplers able to provide high values of output power division ratios. Radiation patterns with SLLs far lower than −23 dB are achieved, without the use of any additional circuitry, in opposition to the case of simultaneous port excitation. Apart from SLL reduction, the switched line-phase shifter technique is applied in order to increase the number of radiated beams and improve scanning coverage. The beamformers are suitable for interference suppressing point-to-multipoint ground communications, satellite and radar/EW/SIGINT systems. Several microstrip circuit prototypes are designed, fabricated, and tested, whereas extended simulation and measurements results are adduced.