N-Way Planar Balanced-to-Balanced Series Feeding Network for Balanced Frequency-Scanning Phased Array

In this article, a novel series feeding network as an N-way balanced-to-balanced structure for balanced frequency-scanning phased array is proposed. Design requirements of the N-way balanced-to-balanced series feeding (BBSF) network are extracted and mixed-mode S-parameters are expressed by using matrix transformation. Designing the BBSF network without using baluns at input and output paths of the network results in the compact and low-loss feeding network, while maintaining the common-mode suppression feature. Furthermore, to have a planar BBSF network, microstrip crossovers are utilized to avoid the use of multilayer PCB design, resulting in the elegant transfer of intersecting RF signals. To validate the proposed structure, a three-way BBSF network is fabricated which shows acceptable mixed-mode measurement results. Also, to demonstrate the performance of the proposed structure, a balanced frequency-scanning phased array is designed employing the proposed feeding network. The measurement results of the fabricated array show that the differential return loss and the differential mode to common mode conversions are better than 20 and 30 dB at 5.85 GHz, respectively. Meanwhile, the fabricated array shows a wide-range beam-scanning capability over its frequency band.