Bandpass filters with 2N+1 transmission zeros at real frequencies

Sergii Litvintsev; Alexander Zakharov

doi:10.3103/S0735272723100035

Authors

Sergii Litvintsev Igor Sikorsky Kyiv Polytechnic Institute, Kyiv, Ukraine https://orcid.org/0000-0002-6171-0036
Alexander Zakharov Igor Sikorsky Kyiv Polytechnic Institute, Kyiv, Ukraine https://orcid.org/0000-0002-1222-1623

DOI:

https://doi.org/10.3103/S0735272723100035

Keywords:

bandpass filter, cross-coupling, frequency response, resonant frequency, transmission zero

Abstract

This paper discusses N-order bandpass filter (BPF) with all mixed couplings between adjacent resonators, and between end resonators and loads. It has (2N +1) transmission zeros (TZ) at real frequencies. To the existing (N +1) TZs generated by mixed couplings, another N TZs are added, which generated by resonators with special properties. Each such resonator is a λ/4 resonator, in which the connection point is located relatively close to the short-circuited end. In this case, the input admittance of the resonator Y(jω) has a pole ω_p, which is located to the right and at a small distance from the main resonant frequency ω₀. This pole ω_p of the Y(jω) function leads to the appearance of a right-handed TZ in a BPF characteristic. If we use N resonators with different connection points, then N additional TZs will appear. The design of that BPF is considered. The measured and simulated frequency responses of the second-order BPF with 5 TZs are presented.

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