Spoof surface plasmon polariton based half-mode substrate integrated waveguide bandpass filter for x

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056

Volume: 13 Issue: 04 | Apr 2026 www.irjet.net p-ISSN: 2395-0072

Spoof surface plasmon polariton based half-mode substrate integrated waveguide bandpass filter for x-band applications

G. Mohan Kumar1 , S. Lakshmi Prasanna2 , M. V. Harsha Bhusanam3, G. M. M. K. Prasad4, K. S. S. S. Jaya Surya5, Punnam Nagaraju6

12345Graduate Student,6Assistant Professor, Department of Electronics and Communication Engineering, Sri Vasavi Engineering College, Tadepalligudem, West Godavari, Andhra Pradesh, India.

Abstract - In this study, two bandpass filters designed forXband applications are introduced, utilizing a combination of hybrid spoof surface plasmon polariton (SSPP) and half-mode substrate integrated waveguide (HMSIW). The transmission properties of these hybrid SSPP-SIW structures are examined, and the impact of changes in their structural parameters is explored. The dumbbell-shaped SSPP demonstrates greater slow-wave effects compared to the rectangle-shaped SSPP when the groove height is the same, making it an ideal option for creating compact, low-loss, and highly integrated microwave and terahertz devices. The lower and upper cut-off frequencies of the hybrid SSPP-HMSIW bandpassfilterscan be independently adjusted by altering the structural parameters of the SIW and SSPP units, respectively. Both proposed filters offer excellent passband performance, operating within the 7.4 to 13.7 GHz frequency range. The simulated results exhibit a low insertion loss of 0.53–0.65 dB and a stable return loss better than 10 dB across the entire operating bandwidth. Furthermore, they provide wide upper-band rejection exceeding 40 dB up to 20 GHz. The physical dimensions are highly compact, measuring approximately 2.1 × 0.5 at the center frequency, ensuring suitability for modern integrated communication systems.

Key Words: Bandpass filter, Spoof surface plasmon polariton, Half-mode substrate integrated waveguide, Xbandapplications.

1.INTRODUCTION

Modern communication systems, including radar and satelliteapplications,increasinglyrequiremicrowavefilters and transmission lines that are high-performing yet compact.Whileconventionalmetallicwaveguidesprovide superior power-handling and minimal loss, their physical bulk and high cost make them difficult for planar circuit integration [1] To address these challenges, Substrate IntegratedWaveguide(SIW)technologyhasemergedasa preferred alternative, combining the benefits of planar transmissionlineswiththeefficiencyofmetallicwaveguides [1]. However, conventional SIW structures still face size limitationsatlowerfrequencies[1],astheytypicallyrequire dimensionsontheorderofaquarterwavelength.

Surface Plasmon Polaritons (SPPs) are electromagnetic excitations capable of confining energy at subwavelength scalesalongmetal-dielectricinterfaces[2].WhileSPPsoccur naturallyatopticalfrequencies[1],metalsbehaveasperfect electrical conductors at microwave frequencies [3], preventingnaturalSPPexistence.Tobridgethisgap,Spoof SurfacePlasmonPolaritons(SSPPs)weredevelopedusing artificialperiodicstructures,suchassubwavelengthgrooves, to mimic the field confinement of natural SPPs. Previous investigationsindicatethatthedispersioncharacteristicsof SSPPs are highly dependent on the periodic structural dimensions[4].

TheHalf-ModeSubstrateIntegratedWaveguide(HMSIW) representsasignificantstepinminiaturizationbybisectinga standardSIWalongaquasi-magneticwall.Thisreducesthe transverse width by approximately50% while preserving theoriginalfieldcharacteristics[1].Toachieveevengreater longitudinalminiaturization,recentresearchhasfocusedon integratingSSPPstructuresintotheHMSIWframeworkto introduce "slow-wave effects" [1]. This hybrid approach combines the low-loss waveguiding of HMSIW with the tunabledispersionandfieldconfinementofSSPPs.

Integratingcorrugatedgroovesonthetopmetallayerof anHMSIWallowsfortherealizationofhybridstructuresthat reduce both transverse and longitudinal dimensions significantly [1]. These hybrid designs naturally support bandpassfilteringbycombiningthehigh-passnatureofthe HMSIW with the low-pass behavior of the SSPP units [5]. Furthermore, adjusting structural parameters allows for independent control of the lower and upper cutoff frequencies[6].Thispaperpresentsthedesignandanalysis of a spoof surface plasmon polariton-based HMSIW optimized for X-band applications, aiming to achieve significant miniaturization compared to conventional approaches[7]

2. DEMONSTRATION OF HYBRID SSPP‐HMSIW BANDPASS FILTERS

2.1

Conventional HMSIW

TheproposedHMSIWstructuresaredesignedusingRogers RT/duroid5880substratewithadielectricconstant of

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2.2,alosstangentof0.0009,andathicknessof0.508mm. Thecoppermetallizationthicknessismaintainedat0.018 mm. As illustrated in Fig. 1a, the conventional HMSIW configuration is implemented based on the optimized parameters detailed in Table 1. By precisely tuning the geometric parameters, particularly the width(a) of the HMSIW,thestructureisconfiguredtooperateasahigh-pass filter.ThesimulatedS-parameters(S11 and S21),aspresented in Fig. 3a, demonstrate the filter's performance with significant insertion and return loss characteristics. This behaviorisattributedtotheefficientconversionofthe TE10 modeoftheHMSIWintothetransitionmode.Itisobserved thatthelowercutofffrequencyisprimarilygovernedbythe HMSIWwidth;hence,forX-bandapplications,thewidthwas optimizedtoachieveaspecificcutofffrequencyof8GHz.

Table -1: Design parameters of rectangle‐shaped hybrid SSPPSIWfilter

from the quasi-TEM mode of the microstrip directly to fundamental TE10 mode of HMSIW. In order to align the momentum of a traditional HMSIW with that of a hybrid SSPP-HMSIW,weproposeusinglinearlygradedrectangular slotstransitioningfromtheregionIboundary(Si)interms oftheirtransversedimensions,asshowninRegionII,thus providing gradient momentum. And also, the rectangular slotsatendaretaperedandtheyallalignedwiththesame slopeasthatofmicrostriptaper.Suchastructureguarantees minimumreflections[14],achievingbroadbandimpedance matching and provides a gradual transition between the lowerTEmodeofHMSIWtoSSPP.Thewidthandlengthof 50Ωmicrostriplinesare W1 =1.6mmand L1 =6.6mm.The initialwidthandlengthoflinearlytaperedmicrostriplines arecalculatedfrom[13].

2.2 HMSIWLoaded withRectangular-shaped SSPP’S

Initially,thehybridSSPP‐HMSIWstructure,asshownin Figure1b,isinvestigatedbyvaryingthegradedrectangular slotsheightsofh(i=1,2,3,4).ThesimulatedS‐parameters are plotted in Figure 3b, It is clear that the value of performance can be improved when the graded slots are linearandmatchedtothemicrostriptaperslopewithagood conversion of the SSPP TE10 mode in the HMSIW to the requiredmode․

The configurations of the hybrid SSPP-HMSIW filters are showninFigure 1b․Theseconfigurationsare dividedinto threeparts:themicrostriptoHMSIWtransitionpart(Region I), the HMSIW to SSPP transition part (Region II), and the hybrid SSPP-HMSIW part (Region III)․ In Region I, the broadband impedance matching element is constructed usingalinearlytaperedmicrostripline[13-15]toallowfor an efficient transition between the 50 Ω input/output feedlineandHMSIW,aswellasenableasmoothtransition

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Figure-1: (a)configuration of conventional HMSIW, (b) Rectangleshaped(topview,filterI),(c)Dumbbell‐shaped (topview,filterII)

They are optimized using EM simulations, and the parameters are set as W2= 2.32 mm and L2=3.4mm.The lengthoftheHMSIWsection L3 is28mm.Thevariationin the width of HMSIW of a rectangle‐shaped SSPP‐HMSIW structure with the groove height of 3.5mm is depicted in Figure2a,Itisclearthatthelowercut-offfrequencyofthe passbandcanbeadjustedindependentlywithminimalorno effect on the upper cut-off frequency. Figure 2b demonstrates that the upper cut-off frequency can be modifiedindependentlybychangingtheperiodicityofthe rectangulargrooveswhilemaintainingtheHMSIWwidthat 7.2mm,althoughthishasaslightimpactonthelowercut-off frequency,primarilyduetothereducedcouplingbetween theHMSIWandSSPPunits.

2.3 HMSIW Loaded with Dumbbell-shaped SSPP’S

TheconsistentfeaturesfordifferentHMSIWwidthsandthe grooves periodicity in a dumbbell-shaped SSPP-HMSIW scenario can be determined. Figure 2c illustrates the transmission coefficients for various radii of a dumbbellshaped hybrid SSPP-HMSIW structure, maintaining a constantgrooveheightof3.5mm.Increasingtheradiusof thedumbbellallowstheuppercut-offfrequencytoshiftto therightindependently,withoutaffectingthelowercut-off frequency. The material parameters for the filters are the same as mentioned above. The design parameters of the rectangle shaped hybrid SSPP‐HMSIW filter are given in Table1.Fordumbbell‐shapedhybridSSPP‐HMSIWfilter,the design parameters are the same as for rectangle‐shaped case,onlytheheightofgroovehischangedto3.2mmand theradiusofdumbbellrischosenas0.3mm.

Figure-2: Simulated transmission coefficients of the proposed hybrid SSPP‐HMSIW structures. (a) Different widthsofHMSIWwithrectangularshapedSSPP,(b)Different periodicitiesofrectangular‐shapedSSPP,(c)Differentradiiof dumbbell‐shapedSSPPwithfixedh=3.5mm

The simulated and measured S‐parameters of the rectangle‐shaped hybrid SSPP‐HMSIW bandpass filter are plottedinFigure3b.TheBWrangesfrom7.4to13.7GHzfor |S 11| < −10 dB and |S 21 | > −1 dB, covering the whole X‐bandof8–12GHz.Averygoodreturnloss(RL)ofmore than10dBinthe wholepassbandhasbeenachieved.The upperout‐of‐bandrejectionisbetterthan42.5dBfrom15.6 to 20 GHz. Figure 3c shows the simulated and measured S‐parametersofthedumbbell‐shapedSSPP‐HMSIWfilter.Its 10‐dBpassbandrangesfrom7.4to13.7GHzwithareturn lossofgreaterthan10dBandinsertionloss(IL)lessthan1 dBinthewholepassband.Theupperstopbandattenuation ismorethan41dBfrom15.6to20GHz.Theroll‐offrateof thefiltersisalsoveryhigh.

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Table -2: Performance comparison with the existing hybrid SSPP‐HMSIWfilters

Figure-3: (a) S‐parameters of the conventional HMSIW, (b)S‐parameters of the rectangle‐shaped SSPP‐HMSIW bandpass filter, (c) S‐parameters of the dumbbell‐ shaped SSPP‐HMSIWbandpassfilter

This work

Table2illustratesacomparisonoftheperformancebetween the newly developed hybrid SSPP‐HMSIW filters and the existing models. The newly designed filters exhibit remarkable efficiency both in the pass band and beyond. Theyexcelinnearlyallparameterswhencomparedtothe current hybrid SSPP‐HMSIW filters. By incorporating the fewestpossibleSSPPunits(onlythree)andimplementing linearlygradedslotsfortheoptimaltransitionfromHMSIW toSSPPmode,theresultingdesignsarenotablycompact.

3. CONCLUSION

Inthisstudy,twoadvancedhybridSSPP-HMSIWbandpass filters,incorporatingrectangle-anddumbbell-shapedSSPPs, have been successfully designed and analyzed for X-band applications. The investigation reveals that the dumbbell-

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shaped SSPP exhibits more significant slow-wave effects compared to the rectangle-shaped SSPP for an identical grooveheight,makingitanidealcandidateforcompact,lowloss,andhighlyintegratedmicrowaveandTHzdevices.The proposeddesignallowsfortheindependentadjustmentof loweranduppercut-offfrequenciesbytuningthestructural parametersoftheHMSIWandSSPPunits,respectively.By employinglinearlygradedslots,anoptimalmodeconversion fromHMSIWtoSSPPwasachieved.Bothfiltersdemonstrate superior passband performance within the 7.4–13.7 GHz range,characterizedbyaremarkablylowinsertionlossof 0.53–0.65dBandaconsistentreturnlossexceeding10dB. Furthermore, the filters provide substantial upper-band rejection(over42.5dBforFilterIand41dBforFilterII)up to20GHz.Withahighlycompactfootprintofapproximately 2.1 × 0.5 , these filters are significantly shorter than existing hybrid SSPP-HMSIW designs, ensuring their suitability for modern communication systems. Future researchwillfocusontheBlochanalysisoftheseSSPP-SIW structurestofurtherexploretheirperiodicproperties.

REFERENCES

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[3] J. Y. Yin, J. Ren, H. C. Zhang, B. C. Pan, and T. J. Cui, “Broadbandfrequency-selectivespoofsurfaceplasmon polaritons on ultrathin metallic structure,” Scientific Reports,2015.

[4] S. A. Maier, S. R. Andrews, L. Martín-Moreno, and F. J. García-Vidal, “Terahertz surface plasmon-polariton propagation and focusing on periodically corrugated metalwires,” Physical Review Letters,2006.

[5] D.-F. Guan, P. You, Q. Zhang, K. Xiao, and S.-W. Yong, “Hybridspoofsurfaceplasmonpolaritonandsubstrate integrated waveguide transmission line and its application in filter,” IEEE Transactions on Microwave Theory and Techniques,2017.

[6] P.Chen,L.Li,K.Yang,andQ.Chen,“Hybridspoofsurface plasmonpolaritonandsubstrateintegratedwaveguide broadband bandpass filter with wide out-of-band rejection,” IEEE Microwave and Wireless Components Letters,2018.

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BIOGRAPHIES

Mr. Mohan Kumar G FinalYearB. Tech student in the Electronics & Communication Engineering Department,SriVasavi EngineeringCollege, Tadepalligudem, West Godavari, AndhraPradesh,India

Ms. Lakshmi Prasanna S Final Year B. Tech student in the Electronics & Communication EngineeringDepartment,SriVasavi EngineeringCollege, Tadepalligudem, West Godavari, AndhraPradesh,India

Mr. V. Harsha Bhusanam M Final Year B. Tech student in the Electronics & Communication EngineeringDepartment,SriVasavi EngineeringCollege, Tadepalligudem, West Godavari, AndhraPradesh,India

Mr. M. M. K. Prasad G FinalYearB. Tech student in the Electronics & Communication Engineering Department,SriVasavi EngineeringCollege, Tadepalligudem, West Godavari, AndhraPradesh,India

Mr. S. S. S. Jaya Surya K FinalYear B.TechstudentintheElectronics& Communication Engineering Department,SriVasavi EngineeringCollege, Tadepalligudem, West Godavari, AndhraPradesh,India

Mr. Punnam Nagaraju Completed his M. Tech in 2013 from JNTUK, Hyderabad.Hehastotally11Years ofteachingexperience.Presentlyhe isworkingasAssistantProfessorin theDepartment,SriVasavi EngineeringCollege, Tadepalligudem, West Godavari, Andhra Pradesh, India. His interested Research area is Microwaveandmmwavefilters.