Dual-Band Microstrip Filtering Balun with Flexible Frequency Ratio

In this letter, a design method of dual-band filtering baluns is presented. The filtering balun operating in 2 bands have the characteristic with flexible frequency ratio in this approach. By properly introducing dual-mode resonators, the filtering balun can work at 2 bands and the frequency ratio of these 2 bands could be flexibly controlled. To prove the effectiveness of the proposed design principle, a dual-band filtering balun working at 3.5 and 4.7 GHz is designed and simulated. Eventually, the results of simulation exhibit favorable performance.