Waveguide planar E-plane filter with ultra-wide stopband
Keywords:bandpass filter, millimeter wave, RF hybrid integrated circuit, stopband, evanescent mode waveguide
A waveguide planar bandpass filter for 2-cm wavelength range (13.5–14.5 GHz) with an ultra-wide stopband (up to the 6th harmonic of the central frequency of the bandwidth) is proposed, developed and experimentally investigated in this article. The filter with a bandwidth is designed on the basis of the antipodal fin-line (AFL) with an extremely high overlap of ridges, which has an overlap size to a waveguide height ratio is equal to 0.773. It allows to significantly reduce the cross-section of the filter waveguide chamber. The compact waveguide planar transformers located on the same substrate are used as the input and output transformers of the filter. It excludes the influence of inaccuracy in the filter structure adjustment relative to the joints with the supply waveguides. Despite the smallness of the resonators longitudinal dimensions in comparison with the half-wavelength in a AFL, the filter synthesis with an acceptable for practice accuracy can be carried out according to Cohn method, modified for its specified feature. At the same time, the decrease in the filter resonators’ intrinsic Q-factor, associated with a strong overlap of the AFL ridges, leads to dimension correction. However, this correction is performed in one of the common program packages of electrodynamic analysis based on the measuring results of the filter resonators’ intrinsic Q-factor.
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