A Self-Calibration Method for 5G Full-Digital TDD Beamforming Systems Using an Embedded Transmission Line

In this article, a self-calibration method for 5G full-digital time-division duplexing (TDD) beamforming systems is proposed and demonstrated, including the self-calibration for both the transmit (Tx) and receive (Rx) channels. By incorporating an embedded transmission line (ETL) in the antenna array that weakly couples with all the radiating elements, the relative magnitude and phase of each Tx/Rx channel can be obtained with the proposed calibration procedure. Comparing with conventional self-calibration methods, the proposed approach requires simpler hardware and reduced calibration time. As a proof-of-concept example, a 1×8 full-digital TDD beamforming array operating at 3.5 GHz with an ETL is fabricated for validation. To further evaluate the accuracy of the calibration data, the “stepped null” calibration was conducted by the over-the-air (OTA) measurement. It is shown that the root mean square (rms) phase and magnitude errors of the calibration results for the Tx and Rx channels are 5.8°/0.84 and 6.3°/0.91 dB, respectively, which are sufficiently accurate for beamforming in 5G communication systems.