Compact Dual-Band Bandpass Waveguide Filter with H-Plane Inserts

Abstract

A novel compact dual-band bandpass waveguide filter is presented in this paper. H-plane metal inserts with complementary split-ring resonators are implemented as resonating elements in the standard (WR-90) rectangular waveguide. Design starts from the models of the waveguide resonators with two resonant frequencies (9[Formula: see text]GHz and 11[Formula: see text]GHz) using a single flat or folded metal insert. Further, folded inserts are used for the second-order dual-band filter design. The equivalent circuits are proposed for the considered waveguide resonators and filter. A good agreement of the amplitude responses obtained for three-dimensional electromagnetic models and microwave circuits is achieved. Finally, compact dual-band bandpass waveguide filter is proposed as a novel solution using miniaturized inverters for both central frequencies. Compact filter model is further modified in order to obtain solution customized for easier fabrication. For the compact filter model, amplitude response is experimentally verified. The required filter response is preserved, as verified by a good agreement of the results obtained for the original dual-band filter and for the compact filter solutions.

Design of microwave waveguide filters with effects of fabrication imperfections

“…This is an important property for the multi-band filter design. Some of the previously reported printed-circuit discontinuities with multiple resonant frequencies can be found in [3,6,24,[26][27][28].…”

“…This means that each waveguide section representing inverter has to be of the proper length equal to λ g /4 (λ g is guided wavelength in the waveguide), for each center frequency. Therefore, the folded inserts have been introduced as an adequate solution [3,6,25,27,28], being a novel solution at the same time, compared to the available open literature.…”

“…Since dimensions of the CSRRs have not been tuned for the I2 insert, the discrepancy between the parameters of the frequency bands is notable; however, the idea is to present the design possibilities and to point at their influence. The previous model may be simplified by using metal inserts [27,28], instead of the multi-layer planar ones (Fig. 18a).…”

“…The inverter is represented by a waveguide section of length equal to λ g 9GHz /4, inserted between these networks. The details regarding equivalent microwave circuit and the equations used for calculation of the lumped elements parameters can be found in [3,6,25,27,28].…”

“…This way of miniaturization assumes that the normalized lengths of the inverters are the same for both center frequencies, but the resonating inserts are still folded. For the sake of easier fabrication, a solution with flat inserts has been proposed, as more optimal one [3,6,25,28] (Fig. 19a).…”