Design of New Dual-Band Wilkinson Power Dividers With Simple Structure and Wide Isolation

In this paper, a new scheme is proposed for a dual-band Wilkinson power divider (PD) without transmission line (TL) stubs (open- or short-circuited), or additional lumped elements (inductors and capacitors). In comparison with conventional PDs, only three additional TLs are employed. One is utilized to extend the input port, while the others are symmetrically distributed at the two branches. After applying even- and odd-mode analyses to the proposed structure, the exact closed-form design equations for a frequency ratio from 2.0 to 6.5 are derived, considering the largest realizable microstrip line impedance (150 Ω). In addition, a new L-type TL with simple structure, compact size, and high design flexibility is proposed to replace the conventional TL to enhance its performance by introducing a transmission zero between the two passbands, resulting in good out-of-band rejection performance. Finally, two dual-band PDs centered at 1.0 and 3.5 GHz are designed and fabricated to verify the proposed design theory. One is based on the proposed structure, while the other incorporates a couple of L-type TLs to replace the conventional TLs. Good agreement with the simulated and measured results can be observed with a low in-band insertion loss and full ports matching. Moreover, the proposed PD also features a wide isolation band with a reference of 15-dB input port return loss. Moreover, the use of the L-type TL can introduce a good stopband between the two passbands, leading to an improved out-of-band rejection performance.