Design of Coupler-Switch Network and Interference Cancellation Scheme for Highly Scalable Self-Calibration Beamforming Systems

Facing the demand for self-calibration capability in rapidly emerging scalable beamforming systems, a coupler-switch network (CSN) and an interference cancellation scheme are proposed in this article. Distinct from most self-calibration techniques limited to calibrating the elements within a single chip or printed circuit board (PCB), a cross-PCB calibration with high scalability is realized in this work. The CSN is a 2-D scalable circuit to transport calibration signals from element transmitters (TXs) to receivers (RXs) selectively in a planar array. The interference cancellation scheme enables the cancellation of intrinsic internal interferences therein. Resorting to them, phase and amplitude deviations of all the elements in the whole system with an adjustable number of PCBs can be obtained, not merely a chip or a PCB. Besides, additional signal processing circuits and the symmetries of the CSN or array are not required, saving a large space and cost, and significantly widening the technique applicability. A quantitative analysis based on the equivalent circuit and signal flow graph theory is explicated. The proposed technique has been implemented and validated on a 16-element scalable beamforming system in simulations and measurements. The root mean square (rms) errors of the measured deviations are 6.5° and 0.76 dB for RXs, 5.9° and 0.67 dB for TXs with respect to the far-field over-the-air (OTA) calibration.