A class of coupled-line trans-directional coupler with independent or simultaneous tuned frequency, coupling coefficient and phase difference

Abstract

The paper reports on the design of coupled-line trans-directional (CL-TRD) coupler with independent or simultaneous tuned frequency, coupling coefficient and phase difference (PD). Based on the proposed structure, four kinds of couplers are exhibited, including a phase-tuned coupler with arbitrary frequency and coupling, a frequency-tuned coupler with arbitrary coupling and non-standard phase, a coupling-tuned coupler with arbitrary frequency and non-standard phase, a simultaneous frequency-, coupling- and phase-tuned coupler. In the section of theoretical analysis, rigorous closed-form design equations are derived using the even-odd mode analysis. For verification, four prototypes are designed, fabricated and measured. Three of them are couplers with independent frequency, coupling or phase tuned. The designed 3-dB frequency-tuned coupler exhibits a frequency tuning range of 58.8% with a PD of 60°. The coupling-tuned coupler shows a tuning range of 3–15 dB with a PD of 70°. The designed phase-tuned CL-TRD coupler can provide a PD from 45° to 135°. Finally, a coupler with simultaneously frequency-, coupling- and phase-tunable was implemented. It has a wide frequency tuning range from 1.2 GHz to 2 GHz with a tunable coupling from 3 dB to 15 dB, and a tunable PD from 45° to 135°.