Research Article Novel Hexagonal Dual-Mode...

Research ArticleNovel Hexagonal Dual-Mode Substrate Integrated WaveguideFilter with Source-Load Coupling

Ziqiang Xu Gen Zhang Hong Xia and Meijuan Xu

Research Institute of Electronic Science and Technology University of Electronic Science and Technology of ChinaChengdu 611731 China

Correspondence should be addressed to Ziqiang Xu nanterxuuestceducn

Received 19 August 2013 Accepted 16 October 2013 Published 22 April 2014

Academic Editors G De Mey and G Priebe

Copyright copy 2014 Ziqiang Xu et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Hexagonal dual-mode cavity and its application to substrate integrated waveguide (SIW) filter are presented The hexagonal SIWresonator which can combine flexibility of rectangular cavity and performance of circular cavity is convenient for dual-modebandpass filters design By introducing coupling between source and load the filter not only has good selectivity due to twocontrollable transmission zeros but also has a small size by the virtue of its single-cavity structure A demonstration filter witha center frequency of 10GHz and a 3 dB fractional bandwidth of 4 is designed and fabricated to validate the proposed structureMeasured results are in good agreement with simulated ones

1 Introduction

Dual-mode cavity bandpass filters have been widely used inthe development of various wireless communication systemsThe metal waveguide dual-mode filters have excellent per-formance owing to their high 119876 factor and power-handlingcapability However they cannot be easily integrated withmicrowave planar circuits [1 2] Recently the substrateintegrated waveguide (SIW) which is synthesized in a pla-nar substrate with arrays of metallic via provides a low-profile low-cost and low-weight scheme while maintaininghigh performance [3ndash5] Particularly the application of SIWtechnology makes the implement of dual-mode cavity filterswith compact size and easy integration possible [6]

On the other hand filters with multiple transmissionzeros (119879119885s) are required to meet the increasing demands ofmodern communication systems in regards to compact sizeand high selectivity Commonly no more than one 119879119885 canbe obtained in a conventional single-cavity dual-mode filterIn order to generate more 119879119885s many approaches have beenproposed to design dual-mode SIW filters One approachis cascading two adjacent dual-mode rectangular cavitiesto generate up to two 119879119885s in stop band [7] Similarly a

dual-mode filter using two connecting circular cavities withtwo 119879119885s is introduced in [8] However their physical sizeswill become larger because of cascaded structures Anotherapproach can be fulfilled by marshaling the effect of source-load coupling in single cavity By adding a direct signalpath between the source and the load 119873 finite transmissionzeros can be generated In [9] a dual-mode filter using anonresonating node with indirect source-load coupling isproposed and two 119879119885s are obtained in such a single-cavityfilter

Ordinarily conventional dual-mode SIWfilers are alwaysbuilt based on rectangular and circular cavities In our previ-ous work a novel hexagonal resonator using SIW technologyand its applications to trisection filters are proposed in[10] The hexagonal SIW cavity can combine flexibility ofrectangular cavities and performances of circular cavitiesMeanwhile as any of the six sides of a hexagonal resonatorcan be utilized for coupling the filter configuration is veryflexible to design In this paper we present a SIW filterwith dual-mode hexagonal cavity By introducing couplingbetween source and load the filter not only has two 119879119885s toimprove frequency selectivity but also has a small size byprofit from its single-cavity structure

Hindawi Publishing Corporatione Scientific World JournalVolume 2014 Article ID 915740 5 pageshttpdxdoiorg1011552014915740

2 The Scientific World Journal

R1

R2

S L

Sourceload

Resonator

MS1 M1L

MS2 M2L

MSL

Figure 1 Coupling scheme of proposed dual-mode filter

2 Filter Analysis and Design

Figure 1 shows the coupling topology of the proposed dual-mode filter By adding the coupling between the source andthe load one additional 119879119885 can be obtained In other wordsthe source and the load are directly coupled which can addan extra transmission path Under this circumstance thetopology can generate up to two 119879119885s The coupling matrix119872 of the proposed topology can be written as

119872 =[[[

[

0 1198721198781 1198721198782 1198721198781198711198721198781 11987211 0 11987211198711198721198782 0 11987222 1198722119871119872119878119871 1198721119871 1198722119871 0

]]]

]

(1)

The conventional doublet without source-load couplinghas a 119879119885 in the stopband and an explicit expression relatingthe coupling elements and the transmission zero Ω is pro-vided in a low-pass prototype as follows [11]

Ω =11987211119872

2

1198782minus11987222119872

2

1198781

11987221198781minus11987221198782

(2)

Here since the topology exhibits symmetrically therelationships119872

1198781= minus119872

1119871and119872

1198782= minus119872

2119871can be hold

When introducing the source-load coupling into thisdoublet an additional 119879119885 can be obtained To get moreinsight of location of two 119879119885s in this topology an explicitexpression relating119872 and the 119879119885s is given by

Ω = 119886 plusmn (1198872+ 1198882)12

(3a)

where

119886 =1198722

1198781+1198722

1198782

2119872119878119871

minus11987211 +11987222

2

119887 =1198722

1198782minus1198722

1198781

2119872119878119871

minus11987211 minus11987222

2

(3b)

W

Wsl

Wu

Lu

LsWi

Ld

Figure 2 Geometric configuration of the proposed filter

where Ω = (1205961205960minus 1205960120596)FBW is normalized angular

frequencyTo achieve the proposed topology a SIW filter with

hexagonal dual-mode cavity is designed and embedded in aPCB substrate as shown in Figure 2The single cavity operateswith 119879119872

110mode which consists of two intersectant modes

illustrated in Figure 3 Bypass cross-couplings between themodes and sourceload are introduced through symmetricalfeeding structure while source-load coupling is introducedby the up-close input and output ports

As far as we know there is no exacted equation forcalculating the resonant frequencies through geometricalparameters in a dual-mode hexagonal cavity According toconventional resonant frequency formulas of metallic circu-lar waveguide resonators the corresponding resonant fre-quency of 11987911987211 in the hexagonal cavity can be determinedby modified formulas as follows

11989111 =119862

radic120576119903sdot1205831015840

2120587119882 (4)

where 119862 is the speed of light 120576119903is the relative dielectric

constant of dielectric substrate 1205831015840 = 427 is the modified rootcoefficient based on the Bessel function 119891

11is the resonant

frequencies of 11987911987211mode in the hexagonal SIW cavity

Figure 4 shows the relationship between the fitted sizeand the resonant frequency of the hexagonal cavity As can beseen the resonant frequency of 11987911987211 mode decreases whenthe geometrical parameter119882 increases

A feeding technique named current probe is adoptedin the IO SIW design to achieve the transition from SIWto microstrip As the symmetrical inputoutput dominatesthe bypass cross-coupling offset 119871119889 between center line andfeeding structure has obvious influence on the frequencyresponse Figure 5 shows the frequency responses for differ-ent values of 119871

119889 Donate the 119879119885s at the lower and upper

stopbands as 1198791198851and 119879119885

2 respectively 119879119885

2is produced

throughbypass cross coupling thus itmove towards the lowerfrequencieswith increasing values of119871

119889 As119879119885

1is dominated

The Scientific World Journal 3

(a) (b)

Figure 3 The E-field distributions of 119879119872110

degenerated mode (a) left inclined mode and (b) right inclined mode

8

9

10

11

12

13

14

10 11 12 13 14 15 16

Freq

uenc

y (G

Hz)

W (mm)

Figure 4 Resonant frequencies with different values of119882

by source-load coupling its location changes slightly whenvarying the values of 119871119889 The feeding structure is right upon119879119872110

mode hence positions of poles change while varying119871119889 As shown in Figure 5(b) 119875

1and 119875

2shift towards each

other when the value of 119871119889increases

On the other hand the length (119871119906) of inputoutput

current probes in feeding structure determines not only thequality factor (119876 factor) of the filter but also the strength ofsource-load coupling Frequency responses for different val-ues of 119871119906 are illustrated in Figure 6 As shown in Figure 6(a)only 1198791198852 at upper stopband is obtained when the valueof 119871119906 is too small to introduce source-load coupling (eg119871119906 = 50mm) By increasing 119871

119906to implement source-load

coupling 1198791198851 at the lower stopband can be realized Thenthe increase of 119871

119906will result in increasing of source-load

coupling hence 1198791198851moves towards the passband In fact 119871

119906

is a parameter which also influences bypass cross couplingso 119879119885

2shifts away from the center of the passband when the

value of 119871119906increases 119871

119906has impact on 119878

11-parameter similar

to 119871119889 As described in Figure 6(b) 119875

1shifts away from 119875

2and

the passband broadens towards the lower frequencies when119871119906augments To achieve demanded frequency responses

during design process of the proposed dual-mode hexagonalSIWfilter parameter of feed probes should be carefully tuned

3 Experimental Results

To validate the above-mentioned concept a 10GHz hexago-nal SIW filter with a 3 dB fractional bandwidth of 4 is fabri-cated on a PCB substrate with dielectric constant of 22 Thecomplete parameters are finely tuned by using commercialfull wave electromagnetic (EM) simulation software HFSSDetailed dimensions of the proposed filter are illustrated inTable 1 The photograph of the fabricated filter is shown inFigure 7 By virtue of the single hexagonal cavity and flexiblesource-load coupling manner the overall size of the filter is286mm times 286mm times 0508mm

An Agilent E8363B vector network analyzer is usedfor measurement The measured and simulated frequency


111051095

Mag

nitu

de (d

B)

Frequency (GHz)9

0

minus60

minus50

minus40

minus30

minus20

minus10

Ld = 27mmLd = 25mmLd = 23mm

TZ1

TZ2

(a)

1051095

Mag

nitu

de (d

B)

Frequency (GHz)

0

minus40

minus30

minus20

minus10


P2

P1

(b)

Figure 5 Frequency response for different values of 119871119889 (a) 119878

21and (b) 119878

11

9585 11105109

Mag

nitu

de (d

B)

Frequency (GHz)8

0

minus60

minus40

minus20

Lu = 104mm

Lu = 10mmLu = 96mmLu = 5mm

TZ1

TZ2

(a)

1051095

Mag

nitu

de (d

B)

Frequency (GHz)

0


minus40

minus30

minus20

minus10

P2P1

(b)


21and (b) 119878

11

Table 1 Parameters of the proposed filter

Parameter 119882 119882119894119871119889119871119904119882119906119871119906119882119904119897

Value (mm) 139 156 25 416 216 101 91

responses are plotted in Figure 8 The measured result showsa central frequency of 999GHz with a fractional bandwidthof 39 minimum passband insertion loss of 166 dB and in-band return loss greater than 17 dB In addition there are twotransmission zeros located at 96GHz with 356 dB rejectionand 1075GHz with 425 dB rejection respectively The mea-sured results are in good agreement with the simulated ones

except a small frequency shift of 119879119885s and a little discrepancyin the in-band insertion lossThe degeneration of the in-bandinsertion loss may be caused by the test fixture as well as theabrasion on the surfaceOverall themeasured results validatethe feasibility of the proposed design with its high selectivitybeing demonstrated

4 Conclusion

A novel compact hexagonal dual-mode SIW filter with highselectivity is proposed Two 119879119885s are produced to improve thefrequency selectivity by introducing source-load coupling tothe proposed single-cavity filter A filter sample is fabricated


Abrasion

Figure 7 Photograph of the fabricated filter

SimulatedMeasured

Frequency (GHz)9 10 11

0

Mag

nitu

de (d

B)

S21

S11

minus40

minus60

minus20

Figure 8 Simulated and measured results of the fabricated filter

and the measurement results agree well with EM full wavesimulation Its compact size and high selectivity make itsuitable for microwave communication application

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the National Natural ScienceFoundation of China (Grants Nos 61101030 61201001 and61301052) and Fundamental Research Funds for the CentralUniversities of China (Grant no ZYGX2011J132)

References

[1] W-Y Park and S Lim ldquoBandwidth tunable and compact band-pass filter (BPF) using complementary split ring resonators(CSRRS) on substrate integrated waveguide (SIW)rdquo Journal ofElectromagnetic Waves and Applications vol 24 no 17-18 pp2407ndash2417 2010

[2] X-P Chen K Wu and D Drolet ldquoSubstrate integrated waveg-uide filter with improved stopband performance for satelliteground terminalrdquo IEEE Transactions on Microwave Theory andTechniques vol 57 no 3 pp 674ndash683 2009

[3] Z Q Xu P Wang J X Liao and Y Shi ldquoSubstrate integratedwaveguide filter with mixed coupled modified trisectionsrdquoElectronics Letters vol 49 no 7 pp 482ndash483 2013

[4] W Y Park and S Lim ldquoMiniaturized half-mode substrate inte-grated waveguide bandpass filter loaded with double-sidedcomplementary split-ring resonatorsrdquo Electromagnetics vol 32no 4 pp 200ndash208 2012

[5] W Shen W-Y Yin and X-W Sun ldquoMiniaturized dual-bandsubstrate integrated waveguide filter with controllable band-widthsrdquo IEEE Microwave and Wireless Components Letters vol21 no 8 pp 418ndash420 2011

[6] Z Q Xu and H Xia ldquoMiniaturized multilayer dual-modesubstrate integratedwaveguide filter withmultiple transmissionzerosrdquo Progress in Electromagnetics Research vol 139 pp 627ndash642 2013

[7] P-Y Qin C-H Liang B Wu and T Su ldquoNovel dual-modebandpass filter with transmission zeros using substrate inte-grated waveguide cavityrdquo Journal of Electromagnetic Waves andApplications vol 22 no 5-6 pp 723ndash730 2008

[8] Y DongW Hong H Tang and KWu ldquoMillimeter-wave dual-mode filter using circular high-ordermode cavitiesrdquoMicrowaveandOptical Technology Letters vol 51 no 7 pp 1743ndash1745 2009

[9] W Shen X-W SunW-Y Yin J-FMao andQ-FWei ldquoA novelsingle-cavity dual mode substrate integrated waveguide filterwith non-resonating noderdquo IEEEMicrowave andWireless Com-ponents Letters vol 19 no 6 pp 368ndash370 2009

[10] Z Q Xu Y Shi P Wang J X Liao and X B Wei ldquoSubstrateIntegrated Waveguide (SIW) filter with hexagonal resonatorrdquoJournal of Electromagnetic Waves and Applications vol 26 no11-12 pp 1521ndash1527 2012

[11] C-K Liao P-L Chi andC-YChang ldquoMicrostrip realization ofgeneralized Chebyshev filters with box-like coupling schemesrdquoIEEE Transactions onMicrowaveTheory and Techniques vol 55no 1 pp 147ndash153 2007

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Active and Passive Electronic Components

Control Scienceand Engineering

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Hindawi Publishing Corporation httpwwwhindawicom

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Submit your manuscripts athttpwwwhindawicom

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

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Journal of

Advances inOptoElectronics


Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of


Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



R1

R2

S L

Sourceload

Resonator

MS1 M1L

MS2 M2L

MSL

Figure 1 Coupling scheme of proposed dual-mode filter

2 Filter Analysis and Design

Figure 1 shows the coupling topology of the proposed dual-mode filter By adding the coupling between the source andthe load one additional 119879119885 can be obtained In other wordsthe source and the load are directly coupled which can addan extra transmission path Under this circumstance thetopology can generate up to two 119879119885s The coupling matrix119872 of the proposed topology can be written as

119872 =[[[

[

0 1198721198781 1198721198782 1198721198781198711198721198781 11987211 0 11987211198711198721198782 0 11987222 1198722119871119872119878119871 1198721119871 1198722119871 0

]]]

]

(1)

The conventional doublet without source-load couplinghas a 119879119885 in the stopband and an explicit expression relatingthe coupling elements and the transmission zero Ω is pro-vided in a low-pass prototype as follows [11]

Ω =11987211119872

2

1198782minus11987222119872

2

1198781

11987221198781minus11987221198782

(2)

Here since the topology exhibits symmetrically therelationships119872

1198781= minus119872

1119871and119872

1198782= minus119872

2119871can be hold

When introducing the source-load coupling into thisdoublet an additional 119879119885 can be obtained To get moreinsight of location of two 119879119885s in this topology an explicitexpression relating119872 and the 119879119885s is given by

Ω = 119886 plusmn (1198872+ 1198882)12

(3a)

where

119886 =1198722

1198781+1198722

1198782

2119872119878119871

minus11987211 +11987222

2

119887 =1198722

1198782minus1198722

1198781

2119872119878119871

minus11987211 minus11987222

2

(3b)

W

Wsl

Wu

Lu

LsWi

Ld

Figure 2 Geometric configuration of the proposed filter

where Ω = (1205961205960minus 1205960120596)FBW is normalized angular

frequencyTo achieve the proposed topology a SIW filter with

hexagonal dual-mode cavity is designed and embedded in aPCB substrate as shown in Figure 2The single cavity operateswith 119879119872

110mode which consists of two intersectant modes

illustrated in Figure 3 Bypass cross-couplings between themodes and sourceload are introduced through symmetricalfeeding structure while source-load coupling is introducedby the up-close input and output ports

As far as we know there is no exacted equation forcalculating the resonant frequencies through geometricalparameters in a dual-mode hexagonal cavity According toconventional resonant frequency formulas of metallic circu-lar waveguide resonators the corresponding resonant fre-quency of 11987911987211 in the hexagonal cavity can be determinedby modified formulas as follows

11989111 =119862

radic120576119903sdot1205831015840

2120587119882 (4)

where 119862 is the speed of light 120576119903is the relative dielectric

constant of dielectric substrate 1205831015840 = 427 is the modified rootcoefficient based on the Bessel function 119891

11is the resonant

frequencies of 11987911987211mode in the hexagonal SIW cavity

Figure 4 shows the relationship between the fitted sizeand the resonant frequency of the hexagonal cavity As can beseen the resonant frequency of 11987911987211 mode decreases whenthe geometrical parameter119882 increases

A feeding technique named current probe is adoptedin the IO SIW design to achieve the transition from SIWto microstrip As the symmetrical inputoutput dominatesthe bypass cross-coupling offset 119871119889 between center line andfeeding structure has obvious influence on the frequencyresponse Figure 5 shows the frequency responses for differ-ent values of 119871

119889 Donate the 119879119885s at the lower and upper

stopbands as 1198791198851and 119879119885

2 respectively 119879119885

2is produced

throughbypass cross coupling thus itmove towards the lowerfrequencieswith increasing values of119871

119889 As119879119885

1is dominated


(a) (b)



8

9

10

11

12

13

14

10 11 12 13 14 15 16

Freq

uenc

y (G

Hz)

W (mm)




1and 119875

2shift towards each








119906








2and







111051095

Mag

nitu

de (d

B)

Frequency (GHz)9

0

minus60

minus50

minus40

minus30

minus20

minus10


TZ1

TZ2

(a)

1051095

Mag

nitu

de (d

B)

Frequency (GHz)

0

minus40

minus30

minus20

minus10


P2

P1

(b)


21and (b) 119878

11

9585 11105109

Mag

nitu

de (d

B)

Frequency (GHz)8

0

minus60

minus40

minus20

Lu = 104mm


TZ1

TZ2

(a)

1051095

Mag

nitu

de (d

B)

Frequency (GHz)

0


minus40

minus30

minus20

minus10

P2P1

(b)


21and (b) 119878

11


Parameter 119882 119882119894119871119889119871119904119882119906119871119906119882119904119897

Value (mm) 139 156 25 416 216 101 91



4 Conclusion



Abrasion


SimulatedMeasured


0

Mag

nitu

de (d

B)

S21

S11

minus40

minus60

minus20





Acknowledgments


References














RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










(a) (b)



8

9

10

11

12

13

14

10 11 12 13 14 15 16

Freq

uenc

y (G

Hz)

W (mm)




1and 119875

2shift towards each








119906








2and







111051095

Mag

nitu

de (d

B)

Frequency (GHz)9

0

minus60

minus50

minus40

minus30

minus20

minus10


TZ1

TZ2

(a)

1051095

Mag

nitu

de (d

B)

Frequency (GHz)

0

minus40

minus30

minus20

minus10


P2

P1

(b)


21and (b) 119878

11

9585 11105109

Mag

nitu

de (d

B)

Frequency (GHz)8

0

minus60

minus40

minus20

Lu = 104mm


TZ1

TZ2

(a)

1051095

Mag

nitu

de (d

B)

Frequency (GHz)

0


minus40

minus30

minus20

minus10

P2P1

(b)


21and (b) 119878

11


Parameter 119882 119882119894119871119889119871119904119882119906119871119906119882119904119897

Value (mm) 139 156 25 416 216 101 91



4 Conclusion



Abrasion


SimulatedMeasured


0

Mag

nitu

de (d

B)

S21

S11

minus40

minus60

minus20





Acknowledgments


References














RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










111051095

Mag

nitu

de (d

B)

Frequency (GHz)9

0

minus60

minus50

minus40

minus30

minus20

minus10


TZ1

TZ2

(a)

1051095

Mag

nitu

de (d

B)

Frequency (GHz)

0

minus40

minus30

minus20

minus10


P2

P1

(b)


21and (b) 119878

11

9585 11105109

Mag

nitu

de (d

B)

Frequency (GHz)8

0

minus60

minus40

minus20

Lu = 104mm


TZ1

TZ2

(a)

1051095

Mag

nitu

de (d

B)

Frequency (GHz)

0


minus40

minus30

minus20

minus10

P2P1

(b)


21and (b) 119878

11


Parameter 119882 119882119894119871119889119871119904119882119906119871119906119882119904119897

Value (mm) 139 156 25 416 216 101 91



4 Conclusion



Abrasion


SimulatedMeasured


0

Mag

nitu

de (d

B)

S21

S11

minus40

minus60

minus20





Acknowledgments


References














RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










Abrasion


SimulatedMeasured


0

Mag

nitu

de (d

B)

S21

S11

minus40

minus60

minus20





Acknowledgments


References














RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









Research Article Novel Hexagonal Dual-Mode...

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