Performance Comparison of Two D-Band E-Plane Cut Waveguide Filters with Complex and Imaginary Transmission Zeros

This paper compares the performance of two eighth-order waveguide filters in D-band. Both filters have a complex pair of transmission zeros, which is used for phase equalization, as well as an imaginary transmission zero pair for blocking improvement in the near passband region. The filters are designed in order to be manufactured in E-plane cut, which reduces the insertion loss compared to H-plane-cut manufacturing. Both filters are designed in a way that a quadruplet section implements the complex transmission zero pair. However, they distinguish each other by the realization of the imaginary transmission zeros. While one filter consists of a second quadruplet section, the other filter has two stub-loaded cavities. The flexibility of both approaches is discussed and a performance comparison of manufactured prototypes takes place.