RF front-end multi-channel amplitude and phase weighting loop for interference mitigation

In order to mitigate the strong electromagnetic interference received by the antenna array, a novel radio frequency (RF) front-end multi-channel amplitude-phase weighting loop circuit is proposed. The circuit can construct a spatial transmission null for the response of each signal channel of the antenna array. When the null angle is aligned with the direction of the interference source, the strong interference can be mitigated. The weighting loop circuit is composed of N circuit elements connected to the N-element antenna array. Each circuit element contains a quadrature coupler (QC) and an amplitude-phase weighting network (APWN). Firstly, the scattering parameter matrix of the circuit element is analyzed, and the amplitude weights and phase weights of the amplitude-phase weighting network are calculated to constrate a null at stop-angle. Then, some factors that have an impact on the circuit response are analyzed, such as the number of arrays, coupling degree of the coupler, array spacing, and array form. According to the results, the general method for guiding the loop circuit design is summarized. Finally, as a proof-of-principle example, the assembled four-element weighting loop circuit is measured at an operating frequency of 1.3 GHz using an injection measurment method. The measured results are in good agreement with the simulation results. At the preset stop-angle, significant transmission nulls have been constructed for the response of all four channels, enabling the loop circuit to achieve at least 20 dB of interference rejection. Meanwhile, the insertion loss to small signals at pass angle is almost zero, which means the circuit does not affect the reception of the desired signal.