The Design Of Planar Multiband Bandpass Filters Based On The Multi-mode Resonators

With the rapid development of the wireless communication industry, more and morecommunication systems are required to work at several frequency channels to reducethe costs. As the crucial device of the transceiver, the frequency selectivity of themultiband filter directly affects the signal quality of the entire communication system.In addition, the dimension of the filter is a very important indicator for the mobilecommunication device. Therefore, the study of the high-performance, miniaturizedplanar multiband filter is a research focus. In this paper, based on the resonantcharacteristic analyses of the stub-loaded mutli-mode resonators and the dual-modesubstrate integrated waveguide (SIW) resonator, several dual-band or tri-band bandpassfilters with different coupling schemes are designed, fabricated, and measured.Firstly, based on the frequency-selective characteristic of the0feeding structure, thesecond passband can be designed by two even-modes, which are introduced by theopen-ended stubs loading on the central of the split ring resonators. The dual-bandbandpass filter designed in this paper possesses three transmission zeros, and the centralfrequency of the second passband can be controlled independently by tuning thedimensions of the open-ended stubs.Secondly, a novel dual-mode SIW resonator was implemented by the slot line on thetop metal surface of the SIW cavity. The initial dimension parameters of the Chebyshevdual-band filter can be extracted by the classic Chebyshev filter design methods. Withthe optimization of the electromagnetic simulator, a dual-passband SIW filter isimplemented, and the central frequency of the second passband can be controlledindependently.In addition, based on the resonant characteristics of the stub loaded dual-moderesonators, two dual-band bandpass filters with different coupling schemes are designed.On this basis, two triple passband responses are introduced by adding one dual-moderesonator or loading two open-ended stubs. Measured results agree with the simulatedresults well, and show good performances.Finally, based on the previous analyses of the stub-loaded resonators, a novel quadruple mode resonator is designed by loading two open-ended stubs and oneshort-ended stub on the half-wavelength resonator. According to the characteristics ofthe resonator, with the cross-coupling of the source and load, a compact dual-passbandfilter with four transmission zeros is fabricated.