This paper proposes novel dual-mode substrate integrated waveguide (SIW) filter and diplexer with circular cavities, in which a pair of symmetrical metallic via perturbations is placed at different positions in a single cavity combining different angle of feeding lines to obtain flexible transmission response. So that multiple transmission zeros can be obtained on one or both sides of the passband. Compared with traditional structure, the proposed dual-mode circular cavity filter and diplexer not only reduce the number of resonators and the volume of filters, but also realize the transmission in higher frequency with the existing machining precision. For verify the structure mentioned above, the dual-mode SIW filter and diplexer are designed, fabricated, and measured in a standard printed circuit board (PCB) process at Q-band. The filter is measured at a central frequency(CF) of 44.86 GHz with a 3 dB fractional bandwidth (FBW) of 10.2%, insertion loss (IL) is 1.9 dB, meanwhile the measured diplexer insertion losses (IL) are 2.1 and 2.4 dB in the lower and upper passbands centered at 38.3 and 44.8 GHz with the fractional bandwidths of 10.7% and 10.1%.The isolation is lower than -40 dB. The measured results show good agreements with the simulated ones.
In this paper, a novel substrate integrated waveguide quasi‐elliptic bandpass filter is proposed by combining single‐ and dual‐mode cavities. Two single‐mode cavities with TE101 mode are directly coupled to the dual‐mode resonance cavity which employs a pair of disturbing metallic via‐holes to make the resonant points of TE101 and TE102 mode in one passband. Based on the conventional box‐like topology, two additional single cavities are used to achieve wider bandwidth and simplify the design difficulty. In addition to two transmission zeros (TZs) realized by the cross‐coupling technology, nonreasoning node will generate an additional TZ at a higher frequency to improve the upper stopband performance. Finally, a sixth‐order filter, having the passband frequency of 24.25–27.5 GHz for 5G application, with three TZs, is simulated, fabricated and measured to demonstrate and verify the proposed structure. The test results show the insertion loss is 1.7 and 3 dB bandwidth is 3.37 GHz. The three TZs improve out of band rejection of the filter.
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