Linear programming solve-predict for tunable couplers with coupling and phase differences

Abstract

The demands for high flexibility in signal phase modulation, operating frequency, and amplitude modulation in contemporary wireless communication systems present challenges for reconfigurable devices. To address this issue, two tunable couplers have been designed, which consist of two parallel microstrips couplers with one-eighth wavelength and phase-shift networks composed of two varactors and coupling lines. Adjusting the even-odd mode impedances of one-eighth wavelength parallel coupled microstrip lines has been established as a means to control the coupling. The alteration of the capacitance of the varactors allows for manipulation of the phase differences in the couplers. Considering the disparities among simulation, manufacturing, and theoretical models, to get the capacitance combinations corresponding to the specific phase differences more quickly and accurately, the linear programming solve-predict method is introduced to this design. Finally, the errors between the predicted values and the theoretical values for the actual values are compared. The relative errors of the theoretical values are not less than 31.76 %, and the maximum errors of the predicted values are not more than 12.5 %, which shows the effectiveness of the method. For demonstration, two couplers operating at 2.4 GHz with different tuning ranges were designed and fabricated, work-1 with a tuning range of 45–135° and work-2 with a tuning range of 0–180° degrees. Based on the standard of 10 dB return loss and 1 dB unbalanced coupling, the relative bandwidths of work-1 and work-2 are not less than 42 % and 25 %. The relative bandwidths of phase differences effective modulation (±5°) are 20.1–42 % and 6–25%, respectively.