Balanced-to-Balanced Series Feeding Network with Common-Mode Suppression

Abstract

In this paper, a balanced-to-balanced series feeding (BBSF) network with common-mode suppression is proposed. Design requirements of the BBSF network is extracted at 2GHz, and constraining rules of the mixed-mode S-parameters are expressed by using matrix transformation. In the proposed structure, in order to obtain an in-phase power division, a balanced input signal is fed from one side of the feeding network into a balanced series of loads, using transmission lines (TLs) with a length of one guided-wavelength (λg). Furthermore, microstrip crossover is used to avoid the use of multilayer PCB design, resulting in the elegant transfer of intersecting RF signals. The simulation and measurement results show acceptable mixed-mode results, confirming that the common-mode suppression is achieved. In the measurements, the differential-mode insertion loss is 4.5 dB, the best differential-mode return loss is 20 dB, and the fractional bandwidth is approximately 15.2%.