A dual-band filtering crossover with large frequency ratio for microwave and millimeter-wave applications

Modern wireless communication systems require components that can support microwave and millimeter-wave bands simultaneously. However, it is difficult for the existing dual-band crossover configurations to achieve a frequency ratio larger than 5. In this letter, a dual-band filtering crossover with a frequency ratio larger than 10 is presented for the first time. To implement such a large frequency ratio, a microstrip filtering crossover operating at microwave band and a substrate integrated waveguide filtering crossover operating at millimeter-wave band are combined through the aperture coupling mechanism. As the two elements almost have no influence on each other, a high degree of design freedom over two bands can be obtained. For demonstration, a dual-band filtering crossover operating at 2.4 and 28 GHz was designed, fabricated, and measured. Measured results are in good agreement with simulated ones, which validates the proposed structure.