Cross-Coupled Substrate Integrated Waveguide Filters With Improved Stopband Performance

Abstract

In this letter, two <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$K$</tex> </formula> -band cross-coupled substrate integrated waveguide (SIW) filters with improved stopband performance are proposed. To implement the negative coupling, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm TE}_{201}$</tex> </formula> -mode response is used in the first cavity, which is also used to implement cross-coupling with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm TE}_{101}$</tex></formula> mode for generating additional transmission zeros (TZs) in the stopband of the filters. For each filter, two additional TZs are introduced and the stopband performance is then improved. The TZ provided by the first cavity can be introduced either below or above the passband, while the TZ provided by the fourth cavity can only be introduced above the passband. The two novel SIW filters are designed at the same center frequency of 20 GHz with the same bandwidth of 600 MHz. The measured data agree well with the simulated results.