Enhanced RF steerable beamforming networks based on butler matrix and rotman lens for ITS applications

This paper presents the design, simulation, and fabrication of two RF steerable beamforming networks (BFN) using a 4×4 Butler Matrix for the 3.15 GHz (S-band) and an 8×8 Rotman Lens for the 6.3 GHz (C-band). Both beamforming networks are intended for the Intelligent Transportation Systems (ITS). Although the frequency range likely to be allocated to such systems is 63 GHz, where the short transmission range allows multiple frequency reuse, both networks are frequency scaled models to verify the concept. The objective of this investigation is to develop steerable antennas suitable for a use in vehicle-to-vehicle and vehicle-to-roadside communications systems. The antenna array feeding network based on Butler Matrix is optimized using a Genetic Algorithm (GA). A GA is used to determine the optimum dimensions for the hybrid couplers and crossovers as the key elements of the network. The Butler Matrix produces orthogonal beams that can be steered in different directions. The lens-based beamformer based on Rotman Lens is capable of generating multiple beams for Electronic Scanning Arrays (ESA) and wide-band operation. To examine the performance of the proposed networks, simulated and measured results are presented and discussed. The results also demonstrate GA´s appropriateness to hybrid couplers and network optimization and enhancement to develop well-established designs for systems that can be used in vehicular telematics and ITS applications.