Design of Frequency Compensated Six-Port Junction and its Application in Microfluidic Sensing

In this letter, a frequency compensated six-port junction and its application in microfluidic sensing are proposed. The six-port circuit consist of 1 direct coupler, 3 hybrid couplers and 2 Wilkinson power dividers. By optimizing the length of the microstrip lines, the phase condition is satisfied based on the evenly distributed circle centers of six-port feature parameters. The best operating bandwidth of the proposed six-port junction prototype is from 2.5 to 2.8 GHz. Then, the experimental system is built which utilizes a nonlinear iterative calibration with 4 calibrated elements and an error box algorithm to calibrate the six-port circuit. By using the calibration model, the reflective coefficients of the microfluidic sensing resonator are calculated by a nonlinear iterative algorithm with linear solution as the initial value. The average measurement errors of the obtained magnitude and the phase are 0.051 and 23.807°. Its resonant frequency can be calculated accurately, which determined the microfluidic solution con-centration. The accuracy of the proposed structure provides a low-cost portable method for microfluidic measurements.