Miniaturized Single-Ended-to-Balanced Arbitrary Four-Section Coupled-Line Coupler With Inherent Impedance Matching

In this brief, a single-ended-to-balanced arbitrary four-section coupled-line coupler with inherent impedance matching is proposed. The proposed coupler consists of four coupled-line sections which achieves a compact circuit layout. Besides, the even- and odd-mode equivalent circuits combining with the standard and mixed-mode S-parameters are adopted to derive the analytical equations. For demonstration, two prototypes operating at 2 GHz with different power division ratios (k = 1 and 3) and different input/output impedances of 50/50 Ω and 50/100 Ω, have been fabricated and measured. The sizes of two prototypes are 0.21 λ_g² and 0.14 λ_g². A good agreement between the simulated and measured results is observed, which demonstrates the validity of the proposed design method and the circuit model.