Realization of Broadband Butler Matrix-based Beamforming Network Using Reconfigurable Synthesized Transmission Lines

Abstract

A broadband beam forming network (BFN) based on a 4-way Butler matrix is proposed to provide full beam steering capability. The key component in fulfilling the design is a broadband tunable power divider (TPD), whose power division ratio (PDR) can be theoretically tuned from –∞ to +∞ with a low reflection coefficient, and with good port to port isolation from 2.16 GHz to 2.64 GHz. The TPD is designed based on phase reconfigurable synthesized transmission lines (PRSTLs) as the tuning elements, in which the characteristic impedance is kept unaltered during phased tuning. In order to achieve continuous beam steering capability, two beam ports of the Butler matrix are excited with an appropriate weighting factor between signals, which is generated and controlled by the TPD. The average transmission loss of the feeding network is -3.5 dB and the average deviation of the progressive phase shift at the output ports is less than 20° from 2.16 GHz to 2.64 GHz.