Planar Balanced‐to‐Balanced Dual‐Channel Combiner With Differential‐ and Common‐Mode Reflectionless Characteristics

ABSTRACT This paper presents a planar balanced‐to‐balanced dual‐channel combiner with differential‐ and common‐mode reflectionless characteristics. The proposed combiner consists of two filtering sections with different center frequencies and two corresponding absorptive networks. The filtering section is realized by a dumbbell‐shaped resonator and a spindle‐shaped resonator, and cross‐coupling is introduced to increase transmission zeros. The absorptive network is realized by two λ /4 open‐circuited coupled lines with resistors loaded at both ends. The proposed absorptive network is connected in parallel with the filtering section and requires only a single structure to achieve reflectionless characteristics for both differential‐mode (DM) and common‐mode (CM). To verify the feasibility of this design, a microstrip prototype with dual‐channel center frequencies of 2.01 and 2.46 GHz was manufactured based on the simulation results. Actual measurements show that for the lower channel, the DM reflectionless band is 1.35–2.56 GHz and the CM reflectionless band is 1.42–2.42 GHz. For the higher channel, the DM reflectionless band is 1.66–3.01 GHz and the CM reflectionless band is 1.73–2.84 GHz.