Design of SPUDT filters on quartz considering waveguide modes

This paper presents an innovative method to achieve maximum performance in SPUDT filters on quartz under particular consideration of waveguide modes. Waveguide modes are known to have a possible strong impact on pass band and transition band performances of SPUDT filters if more than one waveguide mode exists. Consequently, a standard approach is to create a single mode design to prevent it. In some cases, however, it may be advantageous to design a SPUDT filter using several waveguide modes. A patch for the COM theory to analyse the waveguide modes is presented. This method is then used to evaluate possible filter performance degradations caused by parasitic waveguide modes. By means of simulated and experimental results of some filter examples, filter performance is shown which may be achieved by considering or using waveguide modes.