Design of dual-band substrate integrated waveguide filter using frequency transformation method

A dual-band substrate integrated waveguide (SIW) filter is designed in this paper. This design is based on the frequency transformation from the normalized frequency domain to the actual frequency domain, which can calculate the coupling coefficients and the external quality factors analytically. In the realization, the dual-band resonator is utilized to replace each capacitance in the low-pass prototype circuit as the building block of the dual-band filter. To validate the method, a practical SIW dual-band filter is designed and fabricated with passbands at 5.85-5.95 GHz and 6.05-6.15 GHz, respectively, which has a maximum return loss of 15 dB in each passband.