A generalized model of a two-way dual-band Wilkinson power divider (WPD) with a parallel LC circuit at midpoints of two-segment transformers is proposed and compared with that of a conventional two-way dual-band WPD with a parallel LC circuit at the ends of two-segment transformers. The sum of power reflected at an output port and power transmitted to an isolation port from another isolation port in the proposed divider is smaller than that in the conventional divider. Therefore, wide bandwidths for S₂₂, S₃₃, and S₃₂ can be expected for proposed dividers. In the case of equal power division, frequency characteristics of return loss at output ports and isolation of the proposed divider are wider than those of the convention one. The resonant frequencies of LC circuits in the proposed divider and a conventional divider are equal; however, the inductance L used in the proposed divider is always smaller than that in the conventional divider. Design charts and calculated bandwidths as a function of frequency ratio from 1 to 7 are presented. In experiments, two symmetrical and two asymmetrical circuits were fabricated. The experimental results showed good agreement with theoretical results.

A synthesis theory of ultra-wideband (UWB) bandpass (BP) transformer with short-circuited stubs is proposed in this paper. Based on the short-circuited stub number and their positions, six combination topologies are presented when the transmission line (TL) section is fixed to 4. Although analyzing the characteristic functions of these six combination topologies, the same theoretical Chebyshev transfer function can be summarized. Therefore, by selecting different short-circuited stub number and their positions, we can make a flexible choice of the filtering transformer pattern and keep the Chebyshev response at the same time. Finally, by using the proposed transformer, a UWB BP type Wilkinson power divider can be easily designed. In order to match the numbers and frequencies of output ports reflection zeroes (S₂₂ =0)/isolation zeroes (S₃₂ = 0) with those of input port reflection zeroes (S₁₁ =0), one extra TL and one isolation resistor are newly added in the power divider design. One experimental circuit is fabricated, and its measured frequency response verified well the proposed design theory and method.

A generalized two-way two-section dual-band Wilkinson power divider with two absorption resistors and its size-reduced model are presented. Design equations for dual-band and arbitrary power division are derived from modified even- and odd-mode analysis. The frequency ratio of the lower and upper band frequencies must be lower than three. The channel bandwidth is presented as a function of frequency ratio with mathematical expressions. A coupled line section is introduced to reduce circuit size based on the assumptions of linear phase characteristics and equal phase velocities of the even and odd modes. Two two-way dual-band power dividers, one three-way planar dual-band power divider, and one size-reduced dual-band power divider were fabricated. Experimental results were in good agreement with predicted values.

In this paper, a new quadruple-mode stepped-impedance square ring loaded resonator (SI-SRLR) is proposed, and a high-performance dual-band differential bandpass filter (BPF) is developed. Resonant characteristics of the SI-SRLR are investigated by the even-/odd-mode method and simulation techniques. Two differential-modes (DMs) of the SI-SRLR are used to form the dual differential passbands. The admittance ratio K of the SI-SRLR is chosen appropriately to prevent the common-mode (CM) interference with DM operations. Moreover, an open-circuited stub is added to enhance the CM suppression, while a source-load coupling is introduced to produce multiple transmission zeros and improve significantly the frequency selectivity of DM passbands. Finally, a dual-band differential BPF is designed, fabricated, and measured. Good agreement between the simulated and measured results verifies well the proposed structure and design method.

In this letter, a novel compact dual-band filtering power divider (DB-FPD) is proposed. It consists of a U-shaped Wilkinson power divider, two pairs of dual-resonance resonators (DRRs), and a pair of spur lines. With the simultaneous use and appropriate design of the coupled feedlines, mixed electric and magnetic couplings between the DRRs and spur-lines with different lengths, multiple transmission zeros are produced which result in two passbands with desired power division, high-frequency selectivity, good isolation, and an ultrawide stopband. A prototype DB-FPD operating at 2.3 and 3.5 GHz with 3-dB fractional bandwidths of 8% and 6% is designed, fabricated, and measured. The measured responses agree well with the design simulations, exhibiting a stopband up to 13.8 GHz (6f₀) with 20-dB rejection level.