A Novel Decoupling Feeding Network for Circularly Polarized Patch Arrays Using Orthogonal Mode Decomposition

A new decoupling feeding network (DFN) is proposed for circularly polarized (CP) patch arrays with an arbitrary number of elements. Different from linearly polarized (LP) patch arrays, a dual-feed structure is adopted for each element to enhance the CP performance. The dual-feed structures should be integrated into the DFN, and hence the coupling paths become very complicated. An orthogonal mode decomposition (OMD) method is established to analyze the coupling mechanism between the CP patch elements. Based on the OMD, a network model of the mutual coupling between the CP patch elements is established, which can be used to assist design of the DFN. To verify the decoupling effect, a prototype of a $2\times $ 2 CP patch array for a satellite navigation system is fabricated and measured. After applying the DFN, mutual coupling between all ports is reduced to below -33 dB at the center frequency of 1.26 GHz, and the decoupling effects reach 15-23 dB. The CP patch array maintains stable radiation patterns with a realized gain of 9.4 dBi. The proposed OMD approach is applicable to other CP arrays with an arbitrary number of elements.