Millimetre-wave all symmetric edge-coupled bandpass filter

The design of an all symmetric edge-coupled bandpass filter (BPF) at Ka band is presented. Effects of manufacturing tolerances on the design of the edge-coupled bandpass filter are investigated. Consequently, a procedure is devised for a first pass design of such filters. The open-end effect in the half-wavelength resonator section is compensated with the round-ended corners rather than decrementing the lengths in a conventional way. The widths of all the half-wavelength resonators are set equal to avoid discontinuities in the interior of the filter. The fabrication tolerances are compensated in the design prior to manufacturing. The filter is realized on a ceramic filled soft substrate with dielectric constant of 6.2. An in-house customized through-reflect-line (TRL) calibration kit is produced to obtain the de-embedded measured results at the device plane. The measured results are in good agreement with the simulated results. The insertion loss is 3 dB, passband variation is less than 1 dB and the filter exhibits 3dB bandwidth of 3.8 GHz.