This paper presents a novel miniaturized E plane multiband bandstop waveguide filter. Quarter‐wave resonators (QWRs) are printed on a thin dielectric substrate to form an insert that is positioned in the E plane of a rectangular waveguide. Stopbands are designed by simple adjustment of length of the QWRs. QWRs for different stopbands are spaced on the insert to eliminate the unwanted coupling between them. Proposed design exhibits independent tuning of the center frequency and bandwidth of each stopband. Miniaturization is achieved by attaching the QWRs for different stopbands to the opposite waveguide walls. As a proof of concept, dual‐band, and triple‐band E plane waveguide bandstop filters with independent control of designed stopbands (ICDSs) are designed. Further size reduction is made by changing dimensions of the dual‐band filter, leading to the proposed ultracompact filter when designed stopbands are not independently controllable. Next, influence of the individual parameters on the filter response is thoroughly investigated. Novel equivalent electrical circuit is presented for fast filter design. Equivalent circuit of the multiband bandstop filter is a cascade of the equivalent networks of the single‐band bandstop filters. Utilization of the proposed circuit enables design fine‐tuning, thus reducing the number of repeated time and memory‐consuming three‐dimensional electromagnetic (3‐D EM) simulations. To verify the proposed design, an E plane dual‐band ICDS bandstop waveguide filter is fabricated, operating at f01 = 9 GHz with fractional bandwidth (FBW) of 5.77% and f02 = 11 GHz with FBW of 5.27%. Measured results are in good agreement with the 3‐D EM simulation.

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This paper presents results of a study on a bandpass and bandstop waveguide filter design using printed-circuit discontinuities, representing resonating elements. These inserts may be implemented using relatively simple types of resonators, and the amplitude response may be controlled by tuning the parameters of the resonators. The proper layout of the resonators on the insert may lead to a single or multiple resonant frequencies, using single resonating insert. The inserts may be placed in the E-plane or the H-plane of the standard rectangular waveguide. Various solutions using quarter-wave resonators and splitring resonators for bandstop filters, and complementary split-ring resonators for bandpass filters are proposed, including multi-band filters and compact filters. They are designed to operate in the X-frequency band and standard rectangular waveguide (WR-90) is used. Besides three dimensional electromagnetic models and equivalent microwave circuits, experimental results are also provided to verify proposed design. Another aspect of the research represents a study of imperfections demonstrated on a bandpass waveguide filter. Fabrication side effects and implementation imperfections are analyzed in details, providing relevant results regarding the most critical parameters affecting filter performance. The analysis is primarily based on software simulations, to shorten and improve design procedure. However, measurement results represent additional contribution to validate the approach and confirm conclusions regarding crucial phenomena affecting filter response.

U radu se prikazuje nova realizacija mikrotalasnog filtra sa dva nepropusna opsega učestanosti u talasovodnoj tehnici. Četvrttalasni rezonatori realizovani su u planarnoj tehnici, a prilikom istraživanja korišćeni su kao rezonantne prepreke postavljene unutar talasovoda. Razmatraju se rezonatori sa jednom rezonantnom učestanosti i njihove ekvivalentne šeme. Izvršena je detaljna analiza odziva posmatranih rezonatora u cilju projektovanja filtra drugog reda sa jednim nepropusnim opsegom. Ispituje se sprega između dva rezonatora postavljena na istoj štampanoj pločici. Realizovan je filtar drugog reda sa dva nepropusna opsega primenom navedenih rezonatora i predloženog metoda projektovanja. Predloženi metod projektovanja filtara otvara mogućnost za realizaciju filtra višeg reda sa više nepropusnh opsega. Ključne reči: četvrttalasni rezonator, filtar nepropusnik opsega učestanosti, filtar sa dva nepropusna opsega, rezonantna prepreka, talasovodna tehnika SUMMARY NOVEL IMPLEMENTATION OF DUAL-BAND BANDSTOP WAVEGUIDE FILTER USING QUARTER-WAVE RESONATORS Novel implementation of microwave waveguide filter with two rejection bands is presented in this paper. Quarter-wave resonators are implemented in planar technology, and in the research, they are used as resonant septa inserted in the waveguide. Resonators with single resonant frequency are considered, as well as their equivalent circuits. The observed resonator responses are analyzed in details, in order to design second-order filter with a single rejection band. Mutual coupling between the resonators on the same printed-circuit insert is investigated. The second-order filter with two stopbands is implemented using observed resonators and the proposed method for filter design. The proposed method for filter design opens possibility for realization of higher order filters with multi-stopbands.

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