Realization of Even Transmission Zeros for Filter Without Cross-Couplings

A new method is proposed to produce even finite transmission zeros without any cross-coupling between the resonators of filter, by loading the second-order extracted-pole unit (EPU) composed of two mutual coupled resonators at the input or output port of the filter. An arbitrary distribution of finite transmission zeros on the imaginary axis can be achieved by adjusting the resonant frequencies of resonators in the EPUs and the coupling strength between them. The finite transmission zeros can be symmetrically or asymmetrically distributed about the center frequency of the filter, even all on the same side outside the passband of the filter. And the topological structures of these filters are given in this paper. Besides, Cauchy method is adopted to analyze the proposed EPU configuration filter as well. This paper not only discusses how to implement a pair and two pairs of finite transmission zeros, and how to control the distribution of finite transmission zeros, but also gives multiple sets of computer-aided synthesized normalized coupling matrices. Based on this, an eighth-order quasi-elliptic function high-temperature superconducting filter with two pairs of finite transmission zeros was designed on a double-sided YBCO/LaAlO3/YBCO films to verify the feasibility of this new structure.