In this paper, a direct synthesis method is proposed for design and exploration of wideband filtering balun based on a compact triple-mode stacked composite resonators. Accordingly, an equivalent physics-based non-redundant network is developed for interpreting its working mechanism and facilitating the whole design process. Based on the derived non-redundant model, a synthesis approach is then established and described to the efficient design of the proposed filtering balun according to the design specifications. As a result, all the circuit element values and dimensions are directly determined. A wideband filtering balun is then designed to confirm its performance and validate the effectiveness of the proposed synthesis method. In this aspect, a triple-mode wideband filtering balun prototype has been designed, fabricated, and measured. The synthesized, simulated, and measured results are found in good agreement with each other over a wide operating band range, and they have demonstrated the attractive performances of the proposed wideband filtering balun, such as wide bandwidth of operation, sharpened frequency selectivity, good magnitude imbalance, and phase difference.