A simplified on-chip calibration method for branch-line coupler

Abstract

In this paper, we propose a simplified on-chip calibration method for multi-port devices to de-embed the unwanted but unavoidable parasitics introduced by the probing pads as well as the effects originating from redundant feeding lines. The traditional TRL (Thru, Reflect, Line) calibration technique for single-ended two-port device is extended to a classic on-chip branch-line coupler that can be decomposed as the odd-and even-mode equivalent circuit. Accordingly, the TRL calibration standards in the balanced format are designed as well. As a final step, 4-port single-ended S-parameters of device under test (DUT) are reconstructed through its de-embedded odd-and even-mode S-parameters. To validate the efficacy of our proposed method in extracting S-parameters of DUT, models in HFSS, such as the branch-line coupler with probing pads, and modified TRL calibration standards are generated. After performing the de-embedding procedures with the proposed calibration method in this paper, the extracted S-parameters agree well with the simulated S-parameters of DUT without adding any pads and feeding lines for measurement.