Abstract-In this paper, combline substrate integrated waveguide (SIW) filters using electric and magnetic couplings are thoroughly studied. Thus, a negative coupling scheme consisting on an open-ended coplanar probe is proposed and analyzed in detail. Several in-line 3−pole filters at C-band are designed, manufactured and measured showing how the presented approach can be used for implementing direct couplings while enabling an important size reduction and improved spurious-free band compared to conventional magnetic irises. A fully-packaged quasi-elliptic 4−pole filter is also designed at 5.75 GHz showing how the negative coupling structure can be used for introducing transmission zeros by means of cross-couplings between nonadjacent resonators. Finally, average and peak power handling capabilities of these filters have been also analyzed from a multiphysics point of view. Measured results validate the theoretical predictions confirming that combline SIW filters can handle significant levels of continuous and peak power, providing at the same time easy integration, compact size and advanced filtering responses.Index Terms-Cross-coupled filters, electric and magnetic mixed couplings, multiphysics analysis, power handling capabilities, quasi-elliptic filter, substrate integrated waveguide.
In this paper, a novel electric coupling for Sub strate Integrated Waveguide (SIW) bandpass filter is proposed, designed and applied in combline SIW structure. The electric coupling is obtained by means of an open-ended coplanar transmission line which couples comb line SIW resonators. The proposed coupling structure can introduce mixed electric and magnetic coupling thus helping to enhance the filter selectivity. To prove the concept, a quasi-elliptic cross-coupled 4-pole SIW filter is designed including transmission zeros (TZs) at both sides of the pass-band. The filter is centred at 5.75 GHz with absolute bandwidth of 114 MHz (2%). The TZs are set at 5.63 GHz and 5.87 GHz. The measured results confirm the performances of the proposed structure, showing the advantages of wider upper stop-band, higher compactness and easy integration with planar structures.Index Terms-Cross coupling, electric and magnetic mixed coupling, quasi-elliptic filter, substrate integrated waveguide.
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