Automated design of balanced wideband bandpass filters based on mirrored stepped impedance resonators (SIRs) and interdigital capacitors

This paper presents small balanced bandpass filters exhibiting wide differential-mode pass bands and high common-mode suppression. The filters are implemented in microstrip technology and their topology consists of multisection mirrored stepped impedance resonators (SIRs) alternating with mirrored interdigital capacitors. The mirrored SIRs provide the required common-mode transmission zeros to achieve effective rejection of that mode in the region of interest, i.e. the differential-mode pass band. An automated design method for such filters, based on aggressive space mapping, is reported. The method uses the equivalent circuit model of both the mirrored SIRs and the interdigital capacitors, and filter synthesis is based on a quasi-Newton iterative algorithm where parameter extraction is the key aspect. The automated design approach is illustrated through an order-3 filter, where it is demonstrated that the filter topology is generated from the specifications. As compared with previous balanced filters based on mirrored SIRs coupled through admittance inverters, the proposed filters of this work are smaller and the design method is simplified, since bandwidth compensation due to the narrowband functionality of the inverters is avoided.This work was supported by MINECO-Spain (projects no. TEC2013-47037-C5-1-R, TEC2013-40600-R, and TEC2013-49221-EXP), Generalitat de Catalunya (project no. 2014SGR-157), and Institucio Catalana de Recerca i Estudis Avancats (who has awarded Ferran Martin).Sans, M.; Selga, J.; Vélez, P.; Rodriguez Perez, AM.; Bonache, J.; Boria Esbert, VE.; Martin, F. (2016). Automated design of balanced wideband bandpass filters based on mirrored stepped impedance resonators (SIRs) and interdigital capacitors. International Journal of Microwave and Wireless Technologies. 8(4-5):731-740. https://doi.org/10.1017/S1759078716000672S73174084-

Compact Wideband Balanced Bandpass Filters With Very Broad Common-Mode and Differential-Mode Stopbands

[EN] Compact balanced bandpass filters based on a combination of multisection mirrored stepped-impedance resonators and interdigital capacitors are presented in this paper. The considered filter topology is useful to achieve wide bandwidths for the differential mode, with broad stop bands for that mode, as well as very efficient common-mode suppression. By conveniently adjusting the transmission zeros for both operation modes, the differential- and common-mode stopbands can be extended up to significantly high frequencies. Filter size and this differential- and common-mode stopband performance are the main relevant characteristics of the proposed balanced filters. The potential of the approach is illustrated by the design of a prototype order-5 balanced bandpass filter, with central frequency $f_{0} = 1.8$ GHz, 48% fractional bandwidth (corresponding to 55.4% ¿3-dB bandwidth), and 0.04-dB ripple level. The filter is automatically synthesized by means of an aggressive space-mapping software tool, specifically developed, and two (pre- and post-) optimization algorithms, necessary to determine the transmission-zero frequencies. The designed filter is as small as $0.48lambda _{g} times 0.51lambda _{g}$ , where $lambda _{g}$ is the guided wavelength at the central filter frequency, and the differential-mode stopband extends up to at least 6.5 GHz with more than 22-dB rejection. The common-mode suppression is better than 28 dB from dc up to at least 6.5 GHz.This work was supported in part by MINECO-Spain under Project TEC2013-40600-R, Project TEC2016-75650-R, and Project TEC2016-75934-C4-1-R, in part by the Generalitat de Catalunya under Project 2014SGR-157, in part by the Institucio Catalana de Recerca i Estudis Avancats (who awarded F. Martin), and in part by by FEDER funds.Sans, M.; Selga, J.; Vélez, P.; Bonache, J.; Rodríguez Pérez, AM.; Boria Esbert, VE.; Martin Antonlin, F. (2018). Compact Wideband Balanced Bandpass Filters With Very Broad Common-Mode and Differential-Mode Stopbands. IEEE Transactions on Microwave Theory and Techniques. 66(2):737-750. https://doi.org/10.1109/TMTT.2017.2785246S73775066

Design of Capacitively Loaded Coupled-Line Bandpass Filters With Compact Size and Spurious Suppression

[EN] This paper is focused on the synthesis of capacitively loaded coupled lines for the design of bandpass filters with compact size and spurious suppression. The filters consist of cascaded pairs of coupled lines periodically loaded with patch capacitors. The loading capacitances provide a slow-wave effect to the coupled lines useful for filter miniaturization, whereas periodicity introduces bandgaps that can be controlled in order to achieve spurious suppression. Filter design is achieved following an automated process based on aggressive space mapping (ASM) optimization. The two reported examples, a third-order filter with central frequency f0=1.0 GHz, 8% fractional bandwidth, and 0.1-dB ripple level and a fifth-order filter with central frequency f0=1.8 GHz, 8% fractional bandwidth, and 0.1-dB ripple level, demonstrate the potential of the proposed ASM-based design approach, as well as the effectiveness of the loading capacitances to reduce filter size and reject the spurious bands. Significant size reduction in both filters is achieved, whereas the out-of-band rejection is better than 30 and 45 dB in the third-order and fifth-order filters, respectively, up to at least 4f0 .This work was supported in part by MINECO-Spain under Project TEC2013-47037-C5-1-R, Project TEC2013-40600-R, and Project TEC2013-49221-EXP, in part by the Generalitat de Catalunya under Project 2014SGR-157, and in part by FEDER funds. The work of F. Martin was supported by the Institucio Catalana de Recerca i Estudis Avancats. The work of M. Orellana was supported in part by the Universidad de Costa Rica, in part by MICITT, and in part by CONICITOrellana, M.; Selga, J.; Vélez, P.; Sans, M.; Rodríguez Pérez, AM.; Bonache, J.; Boria Esbert, VE.... (2017). Design of Capacitively Loaded Coupled-Line Bandpass Filters With Compact Size and Spurious Suppression. IEEE Transactions on Microwave Theory and Techniques. 65(4):1235-1248. https://doi.org/10.1109/TMTT.2016.2638843S1235124865