Optimisation of SIW bandpass filter with wide and sharp stopband using space mapping

This work presents a substrate integrated waveguide (SIW) bandpass filter with wide and precipitous stopband, which is different from filters with a direct input/output coupling structure. Higher modes in the SIW cavities are used to generate the finite transmission zeros for improved stopband performance. The design of SIW filters requires full wave electromagnetic simulation and extensive optimisation. If a full wave solver is used for optimisation, the design process is very time consuming. The space mapping (SM) approach has been called upon to alleviate this problem. In this case, the coarse model is optimised using an equivalent circuit model-based representation of the structure for fast computations. On the other hand, the verification of the design is completed with an accurate fine model full wave simulation. A fourth-order filter with a passband of 12.0-12.5GHz is fabricated on a single layer Rogers RT/Duroid 5880 substrate. The return loss is better than 17.4dB in the passband and the rejection is more than 40dB in the stopband. The stopband is from 2 to 11GHz and 13.5 to 17.3GHz, demonstrating a wide bandwidth performance.