Sequential Phase Feeding Network Based on Broadside Coupling and Microstrip-to-Slotline Transitions for Circularly Polarized Antennas

A four-port sequential phase feeding network that aims to improve the circular polarization purity of antenna arrays and widen their axial ratio bandwidth is presented. The network uses a broadside-coupled structure integrated with microstrip-to-slotline transitions to achieve wide bandwidth with balanced phase and power division in its four output ports. The network outperforms the existing designs concerning the isolation between the output ports and the balanced amplitude and phase of the four outputs over a wide bandwidth. Those are key factors in achieving a wide axial ratio in circularly polarized antenna arrays. The network is fabricated and tested. The four output ports have equal transmission coefficients with less than ±0.7 dB imbalance and a progressive 90° phase difference with less than ±6° phase variation across the band from 9.6 to 15.3 GHz. Moreover, the network achieves an isolation of 15 dB between its four output ports. Those metrics indicate a significant improvement compared to state-of-the-art. Different types of packaging are studied to enable the device to operate efficiently under various conditions. The results demonstrate the feasibility of protecting and integrating the packaged network with other devices of the wireless system.