Millimeter Wave Microstrip Broadband Bandpass Filters Design and Test

A new design method to achieve, using commercial CAD software, accurately predictable response in microstrip bandpass filters is presented. Filters are based on conventional coupled line microstrip technology and their frequency range is up to 50 GHz. The design method allows to avoid the inaccuracy of electrical models at these frequencies due to the presence of parasitic effects. Limitations of test procedures using coaxial to microstrip transitions are discussed, and an electrical model for this transition has been obtained. Using a very accurate test method, based on coplanar to microstrip transitions and TRL calibration techniques, it is possible to get a very good agreement between simulation and test results.