Narrowband Substrate Integrated Waveguide Isolators

In this letter, two types of X-band ferrite-loaded isolators are proposed based on the substrate integrated waveguide (SIW) technology. First, a full-height E-plane ferrite slab is used to construct low-loss and high-isolation SIW isolators. The insertion loss is less than 2.2 dB and the isolation coefficient is larger than 30 dB within 400 MHz bandwidth. Then, a surface ferrite-loaded isolator is developed to simplify machining process. The ferrite slabs are mounted on the top and bottom surfaces of the SIW, but not inserted into rectangular holes within the SIW. The insertion loss is less than 3.2 dB ranging from 9.79 to 10.4 GHz. Both the return loss and isolation coefficient are better than 20 dB over the same frequency range.