Design of Bandpass Transversal Filters Employing a Novel Hybrid Structure

Abstract—A novel structure for the implementation of compact transversal bandpass filters is proposed in this paper. This new proposal consists of a hybrid structure, based on the combination of two different technologies: the waveguide and microstrip. It is shown that the novel hybrid microwave filter is able to implement both a second- and third-order filtering function with up to two or three transmission zeros, respectively. In this way, a practical implementation of a fully canonical transversal filter with a third degree response is for the first time directly achieved. In addition, the way to control the positions of transmission zeros with the new technology is treated in this paper. It is shown that symmetric or asymmetric responses and also filtering functions with a complex pair of transmission zeros can be easily obtained. To demonstrate the validity of this novel structure, several implementation exam-ples are presented. A prototype has been designed, manufactured, and successfully tested, showing the practical validity of the new structure. Index Terms—Bandpass filters, coupling matrices, resonator fil-ters, synthesis techniques, transmission zeros, transversal filters. I