Design of a broadband diplexer based on substrate integrated plasmonic waveguide

Abstract

In this article, a new wideband diplexer for microwave frequencies is proposed. This diplexer is designed based on the combination of spoof surface plasmon polariton structures with substrate integrated waveguide (SIW) structures. In the proposed diplexer, bandpass filters were designed within a frequency range of 6–9.2 GHz (bandwidth of 40%) and 11.7–16.2 Hz (bandwidth of 29%) by creating rectangular grooves on the top and bottom of the metallic layers of the SIW. These grooves generate surface plasmon waves in the SIW structure that limit the dispersion curve to an asymptotic frequency and cause a high cut‐off frequency. The low cut‐off frequency of the filters is determined by the SIW dimensions. Moreover, the two filters were fed using a microstrip T‐junction with stepped impedance transformation. By optimizing the feed lines, the electromagnetic waves in each working band are directed to the filter of that band, and finally, the filters create a proper attenuation outside the band. A sample of the diplexer is fabricated and tested to verify the design. The simulation results are in good agreement with the experimental results. This diplexer can be a good candidate in microwave frequencies for telecommunication systems.

Substrate Integrated Waveguide Multiband Bandpass Filters and Multiplexers: Current Status and Future Outlook

“…6. As can be seen, various matching networks can be exploited and combined with diverse SIW single-band BPFs to develop SIW multiband BPFs and multiplexers based on this scheme, embracing multiport wideband T-junctions based on SIW [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38] or microstrip [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49], [50], [51], [52], [53] technologies, circulators [31], manifolds [32], coupling apertures [54], [55], switches [56], shared feeding ports [57],…”

“…Microstrip T-junctions are the other type of frequently used matching circuits in the development of SIW multiband BPFs and multiplexers [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49], [50], [51], [52], [53] thanks to their wideband matching characteristics and significant flexibilities. The representative works using microstrip T-junctions have been described in Fig.…”

“…8(b). For a further circuit miniaturization, SIW loading techniques including CSRRs-loaded SIW [49], composite right/left-handed (CRLH) cells-loaded SIW [50], spoof surface plasmon polariton (SSPP) [51] and SSPPs-loaded SIW [52], [53] schemes were applied to realize at least one channel of the diplexers or triplexers, as the two prototypes shown in Fig. 8(c).…”

“…18. Some of these schemes have also been applied to design miniaturized SIW multiband BPFs and multiplexers, such as using LTCCbased multilayered configurations [40], [62], [69], [73], [75], [111], [131], partial-mode techniques [53], [64], [82], [90], [94], [105]- [107], [128], folded [25] and ridged [32] schemes, and metamaterial cells-based solutions [33], [34], [35], [36], [37], [49], [50], [51], [52], [53]. It is worthwhile mentioning that these miniaturization schemes would usually lead to the increasing of transmission loss of an SIW transmission structure or the lowering Q u of an SIW resonant cavity.…”

“…Because all the multiple passbands operate below the cut-off frequency of SIW transmission structure, miniaturization can be achieved for this kind of loading solutions. Nevertheless, it is usually difficult to realize cross-coupled topologies except conventional inline topologies, and the self-packaged characteristic of SIW structures would be destroyed due to the radiation property of CSRRs, needless to say lowering their unloaded quality factors Q u s.Microstrip T-junctions are the other type of frequently used matching circuits in the development of SIW multiband BPFs and multiplexers[39],[40],[41],[42],[43],[44],[45],[46],[47],[48],[49],[50],[51],[52],[53] thanks to their wideband matching characteristics and significant flexibilities. The representative works using microstrip T-junctions have been described in Fig.8.…”