Research Article Two-Element Tapered Slot Antenna Array ...downloads.hindawi.com/journals/ijap/2014/847475.pdf · Research Article Two-Element Tapered Slot Antenna Array for Terahertz

Research ArticleTwo-Element Tapered Slot Antenna Array forTerahertz Resonant Tunneling Diode Oscillators

Jianxiong Li1 Yunxiang Li1 Weiguang Shi1 Haolin Jiang1 and Luhong Mao2

1 School of Electronics and Information Engineering Tianjin Polytechnic University Tianjin 300387 China2 School of Electronic Information Engineering Tianjin University Tianjin 300072 China

Correspondence should be addressed to Jianxiong Li lijianxiongtjpueducn

Received 23 June 2014 Revised 29 August 2014 Accepted 3 September 2014 Published 14 October 2014

Academic Editor Jaume Anguera

Copyright copy 2014 Jianxiong Li 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

Two-element tapered slot antenna (TSA) array for terahertz (THz) resonant tunneling diode (RTD) oscillators is proposed inthis paper The proposed TSA array has the advantages of both the high directivity and high gain at the horizontal directionand hence can facilitate the horizontal communication between the RTD oscillators and other integrated circuit chips A MIM(metal-insulator-metal) stub with a T-shaped slot is used to reduce the mutual coupling between the TSA elements The validityand feasibility of the proposed TSA array have been simulated and analyzed by the ANSYSANSOFTrsquos High Frequency StructureSimulator (HFSS) Detailedmodeling approaches and theoretical analysis of the proposed TSA array have been fully addressedThesimulation results show that themutual coupling between the TSA elements is reduced below minus40 dB Furthermore at 500GHz thedirectivity the gain and the half power beamwidth (HPBW) at theE-plane of the proposedTSA array are 1218 dB 1309 dB and 61∘respectively The proposed analytical method and achieved performance are very promising for the antenna array integrated withthe RTD oscillators at the THz frequency and could pave the way to the design of the THz antenna array for the RTD oscillators

1 Introduction

The terahertz (THz) frequency ranging from 100GHz to10 THz has recently attracted a large number of interestsin lots of applications such as radio astronomy biologicalmonitoring nondestructive evaluation and information andcommunications technology (ICT) [1ndash4] To realize the appli-cations above the resonant tunneling diodes (RTDs) havebeen seen as good candidates for the THz oscillators workingat room temperature [5ndash7] In addition the good antenna isalso considered as the key component for THz oscillatorswhich can improve the sensitivity of the oscillators to one totwo orders of magnitude

Among the various implementations of antennas inte-grated with the RTD oscillators the patch antennas includingthe rectangular patch antenna [8] and the circular patchantenna [9] have the advantage of achieving the oscillationfrequency at the THz band without using the Si lens Besidesthe offset-fed slot antenna introduced by Hinata et al[10] and implemented by having the feeding point deviatedfrom the center of the slot antenna has drawn considerable

attention due to the fact that the oscillator has a high outputpower of 200 uW with the potential of oscillating up to2 THz The antennas above designed in planar structurehave the vertical radiation pattern However in some specialapplications such as the wireless data transmissions anantenna with the horizontal radiation pattern applicableto the horizontal communication is preferable Thus thetapered slot antennas (TSAs) are ideal options since they canmaintain the directivity approximate to horn antennas Atpresent most researches on TSAs are concentrated on themillimeter wave band [11ndash14] Very recently the TSAworkingat 405GHz was reported in [15] whose directivity is 89 dBHowever the main content of [15] is centered on the RTDand there is little information and theoretical analysis abouthow the TSA is designed and matched with the RTD

The output power of the RTD oscillators integrated withthe antenna is usually low (simuW level) [8ndash10 16ndash19] Toimprove the output power designing antennas with highdirectivity and high radiation efficiency is one effective wayFurthermore the design of the antenna array which canachieve the output power combination of the RTD oscillators

Hindawi Publishing CorporationInternational Journal of Antennas and PropagationVolume 2014 Article ID 847475 8 pageshttpdxdoiorg1011552014847475

2 International Journal of Antennas and Propagation

is another effective method Recently the offset-fed slotantenna array for the RTD oscillators is reported in [20]which achieves the individual output powers of 19 uW at329GHz and 26 uW at 332GHz respectively When the twooscillators are driven simultaneously a single peak outputpower of 51 uW is obtained at 321 GHz which is little largerthan the summation of the individual output power Thisoutcome is rather significant in obtaining the high outputpower of the RTD oscillators which illustrates the feasibilityof the design of the oscillators array However there is littleinformation about the modeling approaches and simulationresults of the antenna array

In this paper the detailed modeling approaches andtheoretical analysis of a high directivity and high gainTSA array for THz RTD oscillators are proposed To ourknowledge this is the first time to apply the TSA arrayintegrated with the RTD oscillatorsThematching conditionsbetween the RTD and the TSA element have been fullyconsidered and addressedTheMIM (metal-insulator-metal)stub with a T-shaped slot is used to reduce the mutualcoupling between the TSA elements The validity and feasi-bility of the proposed TSA array have been simulated andanalyzed by ANSYSANSOFTrsquos High Frequency StructureSimulator (HFSS) The simulation results show that thedirectivity and the gain of the TSA array have been greatlyimproved compared with the TSA element Furthermorethe mutual coupling between the TSA elements has beengreatly reduced and the side lobes of the proposed TSAarray have been greatly supressed The proposed analyticalmethod and achieved performance are very promising for theantenna array integrated with the RTD oscillators at the THzfrequency and could pave the way to the design of the THzantenna array for the RTD oscillators

2 Theoretical Analysis of the TSA ElementThe TSAs belong to the class of directional antennas knownas surface-wave antennas which utilize a traveling wavepropagating along the antenna structure with a phase velocityVph lt 119888 The TSAs maintain the advantage of producingsymmetric radiation patterns in the planes which are parallelto the substrate (119864-plane) and perpendicular to the substrate(119867-plane) though their geometries are completely planarTo work as a surface-wave antenna the effective substratethickness (119905eff) of the TSA has to obey the following require-ment [21]

0005 lt

119905eff120582

0

= (radic120576

119903minus 1)

119905

120582

0

lt 003 (1)

where 1205820is the free-space wavelength 120576

119903is the relative dielec-

tric constant of the substrate 119905 is the substrate thickness Thebeam width will get wider by using a thinner substrate Thusit is vital to know the upper limit of the substrate thickness

A standard TSA consists of a tapered radiating slotused as a transformer to the free space Among the vari-ous types of the TSAs the most common are the linearlytapered slot antenna (LTSA) the exponential tapered slotantenna (ETSA) and the constant-width tapered slot antenna(CWSA) [22] Usually the beam width of the CWSA is

Resonator length Waveguide length LTSA length

Heat sink

RTD

MIM reflector

Upper

LowerElectrode

SI-InP

L1 L2 L3

L4w1

w2 120572

x

y

H

SiO2

Figure 1 Schematic structure of the proposed TSA element

the narrowest followed by LTSA and ETSA on the conditionof the same substrate with the same length and aperture sizeHowever the situation described above is opposite for theside lobe level Thus the LTSA is an ideal compromise dueto considering the beam width and the side lobe level

The radiation of the LTSA is restricted into the slotby the metal surface thus the propagation is end-fire Thebandwidth of the LTSA is decided by the maximal andminimal distance of the slot The directivity can be estimatedas

119863 =

4

int

120587

0

(

1003816

1003816

1003816

1003816

119865

119864(120579)

1003816

1003816

1003816

1003816

2

+

1003816

1003816

1003816

1003816

119865

119867(120579)

1003816

1003816

1003816

1003816

2

) sin 120579 119889120579

(2)

where 119865

119864(120579) and 119865

119867(120579) are respectively the directivity

function of the 119864-plane and the119867-planeThe schematic structure of the proposed RTD-integrated

TSA element is demonstrated in Figure 1 which is notthe same proportion as the real size The whole device iscomposed of a resonator a waveguide and an LTSA Adouble-barrier RTD is located in the resonator The upperand lower electrodes of the TSA element are connected tothe correspondent sides of the RTD For heat sink the bridgeconnects the upper edge of the RTD and the upper electrodeis designed much larger than the RTD At one end of theresonator a 100-nm-thick SiO

2is inserted between the upper

and lower electrodes to prevent short The waveguide witha slightly larger width is linked to the other end of theresonator thus the standing wave is formed since the highfrequency electromagnetic waves are reflected at the bothedges of the resonator Finally the THz wave is radiatedhorizontally through the waveguide and the LTSA

The resonator can be equivalent to an offset-fed slotantenna integrated with RTD For the antenna without offsetthe resonant point should satisfy the following conditions[23]

120582

0

2119899

119890

times 119899 = 119897

119899

119890= (

120576

119903+ 1

2

)

minus12

(3)

where 119897 is the length of the offset-fed slot antenna 119899

119890is

the equivalent refractive index and 119899 is a positive integer

International Journal of Antennas and Propagation 3

Emitter

Collector

Resonance level

minusGd

Idc

Vdc

ΔI

ΔV

Figure 2 Potential profile and characteristics of RTD

minusGRTD Cd LTSA GTSA

Figure 3 Equivalent circuit of TSA element integrated with RTDwithout parasitic elements

The impedance of the TSA element increases with theincreasing of the resonator width and the resonant frequencydecreases with the increasing of the resonator length

The potential profile and characteristics of the RTDare shown in Figure 2 we can observe that the RTD iscomposed of two heterobarriers and a quantum well Inthe current-voltage (I-V) characteristics the resonance levelin the quantum well is close to the conduction band edgeof the emitter at the peak current With the increasing ofthe voltage above the peak current a negative differentialconductance (NDC) region exists which corresponds to thenegative differential resistance (NDR) region The oscillationof the RTD integrated with the antenna is obtained in thisregion [24] Therefore because of the NDR of the RTDand the positive resistance of the antenna the conjugateimpedance matching condition between the RTD and theantenna is rather difficult Generally thematching conditionsare analyzed through the equivalent circuit mode

The oscillation of the RTD oscillators integrated with theantenna can be achieved if the following two conditions aremet simultaneously [25]

Re (119884) le 0

Im (119884) = 0

(4)

where 119884 is the total admittance of the antenna and the RTDThe equivalent circuit of the proposed TSA element

integrated with RTD without parasitic elements is expressedas shown in Figure 3 The parasitic elements such as theresistance and capacitance of the upper contact of the RTDthe inductance of the RTD mesa the mesa resistance andthe spreading resistance from the RTD mesa to the lowerelectrode can be neglected here which does not affect the

Table 1 Specifications of the proposed TSA element

Parameters ValueDesign frequency 500GHz10 dB bandwidth gt200GHzPeak directivity gt90 dBRadiation efficiency gt80HPBW gt50∘

Front back to ratio gt10 dB

conclusions of the analysis 119862119889is the inherent capacitance

of the RTD 119871TSA is mainly determined by the TSA elementminus119866RTD is the negative differential conductance (NDC) of theRTD 119866TSA is the conductance of the TSA which representsthe radiation loss of the TSA element Oscillation occurs if119866RTD gt 119866TSA that is the absolute value of the NDC exceedsthe radiation loss of the TSA element

Usually the output power of the RTD oscillators inte-grated with the antenna is low (simuW level) By an approxi-mate analysis the output power is given as [26]

119875 =

119866ANT times (119866RTD minus 119866ANT) Δ1198812

2119866RTD

(5)

where P can be maximized at the condition 119866ANT = 119866RTD2where 119866ANT is equal to the 119866TSA in this paper Furthermoreif the tunneling time and transit time are neglected themaximum value of the output power will be obtained as [27]

119875max =

3

16

Δ119868Δ119881(6)

where Δ119868 and Δ119881 are the current and voltage of the NDRregion

3 Design of the TSA Element

So far there is no unified standard about the design of theTHz antenna for RTD oscillators Several factors which arerather important for the antenna should be fully consideredFirst the antenna should have high directivity and highradiation efficiency for improving the output power of theRTD oscillators as mentioned above Furthermore antennaswith broadband are also necessary which can broaden therange of the application for the RTD oscillators Other factorssuch as the half power beam width (HPBW) and the frontback to ratio are also crucial for designing the antennas forRTDs oscillators The design specification of the proposedTSA element is shown in Table 1

The proposed TSA is designed on the semi-insulting (SI)InP substrate The equivalent refractive index of SI-InP andSiO2are 348 and 197 and their conductances are neglected

The substrate is thinned in order to reduce the radiation lossof the substrate It is assumed that both electrodes are madeof gold (120590 = 452 times 10

7 Sm) and the frequency dependenceof the conductivity is neglected The mesh area of the RTDis 4 120583m2 which is linked to the RTD and the heat sinkConsidering the design specification the parameters of theproposed TSA element are shown in Table 2


Table 2 Parameters of the proposed TSA element

Parameters Value1198711 35 um1198712 890 um1198713 890 um1198714 6 um1199081 8 um1199082 36 um119867 20 um120572 15∘

minus6000

minus5000

minus4000

minus3000

minus2000

minus1000

Frequency (GHz)

000

30000 35000 40000 45000 50000 55000 60000

m1 m2

Name33700005911000

minus99964minus100067

m1m2

X Y

dB (S

11)

dB (S11)

Figure 4 Return loss of the proposed TSA element

By the circuit simulation the NDC of the RTD isminus652mS at 500GHz and the inherent capacitance Cd is38 fF Thus theoretically the admittance of the proposedTSA element is (326 minus 119895 lowast 1184)mS and the correspondingimpedance is (216 + 119895 lowast 785) ohm at 500GHz

The return loss and the impedance versus frequencyof the proposed TSA element are shown in Figures 4 and5 respectively We can observe that the bandwidth of theproposed TSA is 254GHz (from 337GHz to 591GHz S

11lt

minus10 dB) which yields a rather large relative bandwidth of547 Furthermore the impedance of the proposed TSAelement is (220 + 119895 lowast 798) ohm at 500GHz with thecorresponding admittance of (32minus119895lowast116)mS both ofwhichagree very well with the theoretical values

The radiation pattern and the directivity at the 119864-planeof the proposed TSA element at 500GHz are shown inFigures 6 and 7 respectively We can observe that the gainthe directivity and HPBW at the 119864-plane of the proposedTSA element are 958 dB 1038 dB and 59

∘ respectivelyFurthermore the first side lobersquos gain is minus189 dB at 120579 = 39

∘the front back to ratio is 115 dB and the radiation efficiencyis 832

From the analysis of the proposed TSA element abovewe can obtain that the proposed TSA element enjoys abroadband centered at 500GHz high directivity and highgain at the horizontal direction which satisfies the design

30000 35000 40000 45000 50000 55000 60000Frequency (GHz)

000

2500

5000

7500

10000

12500

15000

Impe

danc

e (O

hm)

Re(Z11)Im(Z11)

m1

m2

Name5000000 2202945000000 798285

m1m2

X Y

Figure 5 Impedance of the proposed TSA element

000

1000

90

60

30

0

150

120

dB (Gain Total)

dB (Gain Total)

m1

m2

minus2000

minus1000minus60

minus90

minus120

minus150

minus180

900000 95817390000m2

Name Ang Magm1

minus18921

Frequency = 500GHz 120601 = 90deg


minus30

Figure 6 Radiation pattern of the proposed TSA element at500GHz

specification of the TSA element and lays a good foundationfor the design of the TSA array The problems of the nextstage work are to reduce the mutual coupling between theTSA elements and suppress the side lobes of the TSA array

4 Design and Theoretical Analysis ofthe TSA Array

Theschematic structure of the proposedTSA array integratedwith the RTDs is demonstrated in Figure 8 Two TSAelements are designed linearly in a planar The MIM stubwith a T-shaped slot is used to reduce the mutual couplingbetween the TSA elements The schematic structure of thecoupling part is shown in Figure 9 The coupling part lengthL5 is 100 120583m which is less than a quarter of the wavelength


000 6000 12000 18000

200

1000

1800

dB (D

ir T

otal

)

dB (Dir Total)

Name900000 103790604340 30000

1195567 30000

m1

m1

m2 m2

m3

m3

X Y

minus3000

minus2200

minus1400

minus600

minus18000 minus12000 minus6000

120579 (deg)


Figure 7 Directivity of the proposed TSA element at the 119864-plane at500GHz

C ou p lin g p a r t

RTD1

RTD2

Upper

Upper

Lower

Lower

Electrode

Electrode

MIM reflector

MIM reflectorSI-InP

SiO2

SiO2

Coupling part

Figure 8 Schematic structure of the proposed TSA array integratedwith RTDs

The slot width w3 is 10 120583m in the lower electrode which isused for bias separation

The oscillationmodes of the two-element RTD oscillatorsarray can be divided into the even mode and the odd modewhen RTD

1and RTD

2are operated simultaneously Two

RTDs are assumed to be the same The oscillation frequencyof the even mode 120596(119890) and the oddmode 120596(119900) can be obtainedas [28]

120596 = 120596

(119890) and 120596

(119900)

= 120596

1

[

[

radic

1 + (

120596

1119871

2

Im (119884

12))

2

∓

120596

1119871

2

Im (119884

12)

]

]

(7)

where 120596

1is the angular frequency when RTD

1is operated

solely L is the inductance mainly determined by the antenna

Lower electrodeL5

MIM stubElectrodeUpper

Lower

w3w3

SiO2

Figure 9 Schematic structure of the coupling part

30000 35000 40000 45000 50000 55000 60000Frequency (GHz)

000

dB(S11)dB(S21)

dB(S22)

S-pa

ram

eter

s (dB

)

minus7000

minus6000

minus5000

minus4000

minus3000

minus2000

minus1000

Figure 10 119878-Parameters versus frequency of the proposed TSAarray

and the coupling part and 119884

12represents the coupling

characteristic If Im(119884

12) gt 0 the frequency of the evenmode

is lower than the other and only this mode is stableThe combined output power of the two-element RTD

oscillators array in the even mode and odd mode is propor-tional to

1003816

1003816

1003816

1003816

119883

1+ 119883

2

1003816

1003816

1003816

1003816

2

=

4 (1 + Re (120581)) even mode0 odd mode

(8)

where 119883

119899is the normalized complex amplitudes which

satisfies |119883119899|

2

= 1 and 120581 is the coupling parameter given as

120581 = minus

119884

12

(119886 minus 119866

119871)

119886 = (

3

2

) (

Δ119868

Δ119881

)

(9)

where 119866119871is the conductance determined by the antenna and

coupling part It can be seen from (8) that the combinedoutput power of the two-element RTD oscillators array isabout four times of a single oscillator in the evenmode whilezero in the odd mode

The S-parameters versus frequency of the proposed arrayis shown in Figure 10 We can observe that 119878

11and 119878

22are

nearly coincident besides the 119878

21is below minus40 dB which


30000 35000 40000 45000 50000 55000 60000Frequency (GHz)

000000

000005

000010

000015

000020

m1

Namem1

X Y

000015000000

Re(Y12)Im(Y12)

minus000015

minus000010

minus000005

Y12(S)

Figure 11 Admittance 119884

12

versus frequency of the proposed TSAarray

dB (Gain Total)

dB (Gain Total)

minus2000

minus1000

900000

000

1000

90

60

30

0

150

120

m1

m2

121814410000 10954m2

Name Ang Magm1

minus30

minus60

minus90

minus120

minus150minus180



Figure 12 Radiation pattern of the proposed TSA array at 500GHz

means that the MIM stub works very well in reducing themutual coupling between the TSA elements

The admittance11988412versus frequency of the proposedTSA

array is shown in Figure 11We can observe that the imaginarypart of 119884

12is positive thus the two-element RTD oscillators

can work in the even mode and achieve the output powercombination

The radiation pattern of the proposed TSA array is shownin Figure 12 We can observe that the gain of the proposedTSA array is 1218 dB at the horizontal direction which is26 dB larger than the gain of the TSA element Furthermorethe first side lobersquos gain is 11 dB at 120579 = 41

∘ and the front backto ratio is 213 dB From the analysis of the radiation patternof the TSA array we can obtain that the TSA array enjoys ahigh gain at the horizontal direction and the side lobes havebeen greatly suppressed

000 6000 12000 18000

200

1000

1800

dB (D

ir T

otal

)

m1

m2 m3

dB (Dir Total)

Name900000 130858589770 30000

1208521 30000

m1m2m3

X Y

minus18000 minus12000 minus6000minus3000

minus2200

minus1400

minus600

120579 (deg)


Figure 13 Directivity of the proposed TSA array at the 119864-plane at500GHz

Thedirectivity of the proposedTSAarray at the119864-plane at500GHz is shown in Figure 13We can see that themaximumhorizontal directivity is 1309 dB which is 271 dB largerthan the directivity of the TSA element Furthermore theHPBW at the 119864-plane is 61∘ which changes little comparedwith the HPBW of the TSA element However the beamwidth of the TSA array becomes narrower at the 119867-planeFinally the radiation efficiency of the TSA array is 812which means that the decrease of the radiation efficiencyis quite little compared with the single TSA element Fromthe analysis of the directivity of the TSA array we canconclude that the proposed TSA array has a very gooddirectivity at the horizontal direction and hence can achievethe horizontal communication between the RTD oscillatorsand other integrated circuit chips

5 Conclusion

The detailed modeling approaches and theoretical analysisof high directivity and high gain TSA array for THz RTDoscillators are presented in this paper The MIM stub with aT-shaped slot is used to reduce the mutual coupling betweenthe TSA elements The simulation results show that thepresented TSA element enjoys high directivity and highgain of 1038 dB and 958 dB at the horizontal directionrespectively When the two TSA elements formed to a lineararray the directivity and gain of the presented TSA arrayare 1309 dB and 1218 dB which are 271 dB and 26 dB largerthan that of the single TSA element respectively The 119878

21

of the TSA array is below minus40 dB which means that themutual coupling between the TSA elements has been greatlyreducedThe first side lobersquos gain is 11 dB thus the side lobesof the TSA array have been greatly suppressed Finally theradiation efficiency of the TSA array is 812 which meansthat the decrease of the radiation efficiency is quite littlecompared with the TSA element Therefore the presentedTSA array has the advantages of both the high directivity andhigh gain at the horizontal direction and hence can achieve


the horizontal communication between the RTD oscillatorsand other integrated circuit chipsThepresented two-elementTSA array can be extended to a multielement array Thepresented analytical method and achieved performance arevery promising for the antenna array integratedwith the RTDoscillators at the THz frequency and could pave theway to thedesign of the THz antenna array for the RTD oscillators

Conflict of Interests

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

Acknowledgments

The authors wish to thank Professor W L Guo School ofElectronic Information Engineering TianJin University forhis continuous encouragement and fruitful discussions Thiswork was supported by the National Natural Science Foun-dation of China (Grants nos 61372011 and No 61331003)

References

[1] M Tonouchi ldquoCutting-edge terahertz technologyrdquoNature Pho-tonics vol 1 no 2 pp 97ndash105 2007

[2] P H Siegel ldquoTerahertz technologyrdquo IEEE Transactions onMicrowave Theory and Techniques vol 50 no 3 pp 910ndash9282002

[3] T Kleine-Ostmann and T Nagatsuma ldquoA review on terahertzcommunications researchrdquo Journal of Infrared Millimeter andTerahertz Waves vol 32 no 2 pp 143ndash171 2011

[4] H-J Song and T Nagatsuma ldquoPresent and future of terahertzcommunicationsrdquo IEEE Transactions on Terahertz Science andTechnology vol 1 no 1 pp 256ndash263 2011

[5] E R Brown J R Soderstrom C D Parker L J Mahoney KM Molvar and T C McGill ldquoOscillations up to 712 GHz inInAsAlSb resonant-tunneling diodesrdquo Applied Physics Lettersvol 58 no 20 pp 2291ndash2293 1991

[6] M Reddy S C Martin A C Molnar et al ldquoMonolithicSchottky-collector resonant tunnel diode oscillator arrays to650 GHzrdquo IEEE Electron Device Letters vol 18 no 5 pp 218ndash221 1997

[7] M Feiginov C Sydlo O Cojocari and P Meissner ldquoResonant-tunnelling-diode oscillators operating at frequencies above 11THzrdquo Applied Physics Letters vol 99 no 23 Article ID 2335062011

[8] R Sekiguchi Y Koyama and T Ouchi ldquoSubterahertz oscil-lations from triple-barrier resonant tunneling diodes withintegrated patch antennasrdquo Applied Physics Letters vol 96 no6 Article ID 0621153 pp 1ndash3 2010

[9] N Sashinaka Y Oguma and M Asada ldquoObservation of tera-hertz photon-assisted tunneling in triple-barrier resonant tun-neling diodes integrated with patch antennardquo Applied PhysicsLetters vol 39 no 8 pp 4899ndash4903 2000

[10] K Hinata M Shiraishi and S Suzuki ldquoSub-terahertz resonanttunneling diode oscillators with high output power (sim200 120583W)using offset-fed slot antenna and high current densityrdquo AppliedPhysics Express vol 3 no 1 Article ID 014001 pp 1ndash3 2010

[11] R Janaswamy and D H Schaubert ldquoAnalysis of the tapered slotantennardquo IEEE Transactions on Antennas and Propagation vol35 no 9 pp 1058ndash1065 1987

[12] I K Kim N Kidera S Pinel et al ldquoLinear tapered cavity-backed slot antenna for millimeter-wave LTCCmodulesrdquo IEEEAntennas andWireless Propagation Letters vol 5 no 1 pp 175ndash178 2006

[13] D S Woo Y G Kim and K W Kim ldquoUltra-widebandmillimeter-wave tapered slot antennasrdquo in Proceedings of theAntennas and Propagation Society International Symposium pp1969ndash1972 IEEE Honolulu Hawaii USA June 2007

[14] I Wood D Dousset J Bornemann and S Claude ldquoLineartapered slot antenna with substrate integrated waveguide feedrdquoin Proceedings of the IEEE Antennas and Propagation SocietyInternational Symposium pp 4761ndash4764 Honolulu HawaiiUSA June 2007

[15] K Urayama S Aoki S Suzuki M Asada H Sugiyama and HYokoyama ldquoSub-terahertz resonant tunneling diode oscillatorsintegrated with tapered slot antennas for horizontal radiationrdquoApplied Physics Express vol 2 no 4 Article ID 044501 pp 1ndash32009

[16] M Asada N Orihashi and S Suzuki ldquoVoltage-controlledharmonic oscillation at about 1 THz in resonant tunnelingdiodes integrated with slot antennasrdquo Japanese Journal ofApplied Physics vol 46 no 5A pp 321ndash324 2007

[17] S Suzuki A Teranishi K Hinata M Asada H Sugiyamaand H Yokoyama ldquoFundamental oscillation of up to 831 GHzin GaInAsAlAs resonant tunneling dioderdquo Applied PhysicsExpress vol 2 no 5 Article ID 054501 pp 1ndash3 2009

[18] M Shiraishi S Suzuki A Teranishi M Asada H Sugiyamaand H Yokoyama ldquoFundamental oscillation up to 915GHz inInGaAsAlAs resonant tunneling diodes integrated with slotantennasrdquo in Proceedings of the 34th International Conference onInfrared Millimeter and Terahertz Waves (IRMMW-THz rsquo09)pp 1ndash2 Busan Republic of Korea September 2009

[19] S Suzuki M Asada A Teranishi H Sugiyama and HYokoyama ldquoFundamental oscillation of resonant tunnelingdiodes above 1 THz at room temperaturerdquo Applied PhysicsLetters vol 97 no 24 Article ID 242102 pp 1ndash3 2010

[20] S Suzuki and M Asada ldquoCoherent power combination inhighly integrated resonant tunneling diode oscillators with slotantennasrdquo Japanese Journal of Applied Physics Part 2 Lettersvol 46 no 45ndash49 pp L1108ndashL1110 2007

[21] K S Yngvesson T L Korzeniowski Y-S Kim E L Kollbergand J F Johansson ldquoTapered slot antenna-new integratedelement for millimeter-wave applicationsrdquo IEEE TransactionsonMicrowaveTheory and Techniques vol 37 no 2 pp 365ndash3741989

[22] K S Yngvesson D H Schaubert T L Korzeniowski E LKollberg T Thungren and J F Johansson ldquoEndfire taperedslot antennas on dielectric substratesrdquo IEEE Transactions onAntennas and Propagation vol 33 no 12 pp 1392ndash1400 1985

[23] S Suzuki and M Asada ldquoProposal of resonant tunneling diodeoscillators with offset-fed slot antennas in terahertz and sub-terahertz rangerdquo Japanese Journal of Applied Physics Part 1 vol46 no 1 pp 119ndash121 2007

[24] N Orihashi S Hattori S Suzuki andM Asada ldquoExperimentaland theoretical characteristics of sub-terahertz and terahertzoscillations of resonant tunneling diodes integrated with slotantennasrdquo Japanese Journal of Applied Physics Part 1 vol 44no 11 pp 7809ndash7815 2005


[25] C S Kim and A Brandli ldquoHigh-frequency high-power opera-tion of tunnel diodesrdquo IRE Transactions on Circuit Theory vol8 no 4 pp 416ndash425 1961

[26] S Suzuki M Shiraishi H Shibayama and M Asada ldquoHigh-power operation of terahertz oscillatorswith resonant tunnelingdiodes using impedance-matched antennas and array configu-rationrdquo IEEE Journal on Selected Topics in Quantum Electronicsvol 19 no 1 Article ID 8500108 2013

[27] M Asada S Suzuki and N Kishimoto ldquoResonant tunnelingdiodes for sub-terahertz and terahertz oscillatorsrdquo JapaneseJournal of Applied Physics vol 47 no 6 pp 4375ndash4384 2008

[28] M Asada and S Suzuki ldquoTheoretical analysis of coupledoscillator array using resonant tunneling diodes in subterahertzand terahertz rangerdquo Journal of Applied Physics vol 103 no 12Article ID 124514 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Active and Passive Electronic Components

Control Scienceand Engineering

Journal of



RotatingMachinery


Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

Acoustics and VibrationAdvances in



Electrical and Computer Engineering

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



is another effective method Recently the offset-fed slotantenna array for the RTD oscillators is reported in [20]which achieves the individual output powers of 19 uW at329GHz and 26 uW at 332GHz respectively When the twooscillators are driven simultaneously a single peak outputpower of 51 uW is obtained at 321 GHz which is little largerthan the summation of the individual output power Thisoutcome is rather significant in obtaining the high outputpower of the RTD oscillators which illustrates the feasibilityof the design of the oscillators array However there is littleinformation about the modeling approaches and simulationresults of the antenna array

In this paper the detailed modeling approaches andtheoretical analysis of a high directivity and high gainTSA array for THz RTD oscillators are proposed To ourknowledge this is the first time to apply the TSA arrayintegrated with the RTD oscillatorsThematching conditionsbetween the RTD and the TSA element have been fullyconsidered and addressedTheMIM (metal-insulator-metal)stub with a T-shaped slot is used to reduce the mutualcoupling between the TSA elements The validity and feasi-bility of the proposed TSA array have been simulated andanalyzed by ANSYSANSOFTrsquos High Frequency StructureSimulator (HFSS) The simulation results show that thedirectivity and the gain of the TSA array have been greatlyimproved compared with the TSA element Furthermorethe mutual coupling between the TSA elements has beengreatly reduced and the side lobes of the proposed TSAarray have been greatly supressed The proposed analyticalmethod and achieved performance are very promising for theantenna array integrated with the RTD oscillators at the THzfrequency and could pave the way to the design of the THzantenna array for the RTD oscillators

2 Theoretical Analysis of the TSA ElementThe TSAs belong to the class of directional antennas knownas surface-wave antennas which utilize a traveling wavepropagating along the antenna structure with a phase velocityVph lt 119888 The TSAs maintain the advantage of producingsymmetric radiation patterns in the planes which are parallelto the substrate (119864-plane) and perpendicular to the substrate(119867-plane) though their geometries are completely planarTo work as a surface-wave antenna the effective substratethickness (119905eff) of the TSA has to obey the following require-ment [21]

0005 lt

119905eff120582

0

= (radic120576

119903minus 1)

119905

120582

0

lt 003 (1)

where 1205820is the free-space wavelength 120576

119903is the relative dielec-

tric constant of the substrate 119905 is the substrate thickness Thebeam width will get wider by using a thinner substrate Thusit is vital to know the upper limit of the substrate thickness

A standard TSA consists of a tapered radiating slotused as a transformer to the free space Among the vari-ous types of the TSAs the most common are the linearlytapered slot antenna (LTSA) the exponential tapered slotantenna (ETSA) and the constant-width tapered slot antenna(CWSA) [22] Usually the beam width of the CWSA is

Resonator length Waveguide length LTSA length

Heat sink

RTD

MIM reflector

Upper

LowerElectrode

SI-InP

L1 L2 L3

L4w1

w2 120572

x

y

H

SiO2

Figure 1 Schematic structure of the proposed TSA element

the narrowest followed by LTSA and ETSA on the conditionof the same substrate with the same length and aperture sizeHowever the situation described above is opposite for theside lobe level Thus the LTSA is an ideal compromise dueto considering the beam width and the side lobe level

The radiation of the LTSA is restricted into the slotby the metal surface thus the propagation is end-fire Thebandwidth of the LTSA is decided by the maximal andminimal distance of the slot The directivity can be estimatedas

119863 =

4

int

120587

0

(

1003816

1003816

1003816

1003816

119865

119864(120579)

1003816

1003816

1003816

1003816

2

+

1003816

1003816

1003816

1003816

119865

119867(120579)

1003816

1003816

1003816

1003816

2

) sin 120579 119889120579

(2)

where 119865

119864(120579) and 119865

119867(120579) are respectively the directivity

function of the 119864-plane and the119867-planeThe schematic structure of the proposed RTD-integrated

TSA element is demonstrated in Figure 1 which is notthe same proportion as the real size The whole device iscomposed of a resonator a waveguide and an LTSA Adouble-barrier RTD is located in the resonator The upperand lower electrodes of the TSA element are connected tothe correspondent sides of the RTD For heat sink the bridgeconnects the upper edge of the RTD and the upper electrodeis designed much larger than the RTD At one end of theresonator a 100-nm-thick SiO

2is inserted between the upper

and lower electrodes to prevent short The waveguide witha slightly larger width is linked to the other end of theresonator thus the standing wave is formed since the highfrequency electromagnetic waves are reflected at the bothedges of the resonator Finally the THz wave is radiatedhorizontally through the waveguide and the LTSA

The resonator can be equivalent to an offset-fed slotantenna integrated with RTD For the antenna without offsetthe resonant point should satisfy the following conditions[23]

120582

0

2119899

119890

times 119899 = 119897

119899

119890= (

120576

119903+ 1

2

)

minus12

(3)

where 119897 is the length of the offset-fed slot antenna 119899

119890is

the equivalent refractive index and 119899 is a positive integer


Emitter

Collector

Resonance level

minusGd

Idc

Vdc

ΔI

ΔV







Re (119884) le 0

Im (119884) = 0

(4)









119875 =


2119866RTD

(5)


119875max =

3

16

Δ119868Δ119881(6)










minus6000

minus5000

minus4000

minus3000

minus2000

minus1000

Frequency (GHz)

000

30000 35000 40000 45000 50000 55000 60000

m1 m2

Name33700005911000


m1m2

X Y

dB (S

11)

dB (S11)




11lt






30000 35000 40000 45000 50000 55000 60000Frequency (GHz)

000

2500

5000

7500

10000

12500

15000

Impe

danc

e (O

hm)

Re(Z11)Im(Z11)

m1

m2

Name5000000 2202945000000 798285

m1m2

X Y


000

1000

90

60

30

0

150

120

dB (Gain Total)

dB (Gain Total)

m1

m2

minus2000

minus1000minus60

minus90

minus120

minus150

minus180

900000 95817390000m2

Name Ang Magm1

minus18921



minus30






000 6000 12000 18000

200

1000

1800

dB (D

ir T

otal

)

dB (Dir Total)

Name900000 103790604340 30000

1195567 30000

m1

m1

m2 m2

m3

m3

X Y

minus3000

minus2200

minus1400

minus600


120579 (deg)




RTD1

RTD2

Upper

Upper

Lower

Lower

Electrode

Electrode

MIM reflector

MIM reflectorSI-InP

SiO2

SiO2

Coupling part




1and RTD



120596 = 120596

(119890) and 120596

(119900)

= 120596

1

[

[

radic

1 + (

120596

1119871

2

Im (119884

12))

2

∓

120596

1119871

2

Im (119884

12)

]

]

(7)

where 120596


1is operated


Lower electrodeL5


Lower

w3w3

SiO2


30000 35000 40000 45000 50000 55000 60000Frequency (GHz)

000

dB(S11)dB(S21)

dB(S22)

S-pa

ram

eter

s (dB

)

minus7000

minus6000

minus5000

minus4000

minus3000

minus2000

minus1000








1003816

1003816

1003816

1003816

119883

1+ 119883

2

1003816

1003816

1003816

1003816

2

=


(8)

where 119883


satisfies |119883119899|

2


120581 = minus

119884

12

(119886 minus 119866

119871)

119886 = (

3

2

) (

Δ119868

Δ119881

)

(9)




11and 119878

22are




30000 35000 40000 45000 50000 55000 60000Frequency (GHz)

000000

000005

000010

000015

000020

m1

Namem1

X Y

000015000000

Re(Y12)Im(Y12)

minus000015

minus000010

minus000005

Y12(S)


12


dB (Gain Total)

dB (Gain Total)

minus2000

minus1000

900000

000

1000

90

60

30

0

150

120

m1

m2

121814410000 10954m2

Name Ang Magm1

minus30

minus60

minus90

minus120

minus150minus180











000 6000 12000 18000

200

1000

1800

dB (D

ir T

otal

)

m1

m2 m3

dB (Dir Total)

Name900000 130858589770 30000

1208521 30000

m1m2m3

X Y


minus2200

minus1400

minus600

120579 (deg)




5 Conclusion


21






Acknowledgments


References
































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










Emitter

Collector

Resonance level

minusGd

Idc

Vdc

ΔI

ΔV







Re (119884) le 0

Im (119884) = 0

(4)









119875 =


2119866RTD

(5)


119875max =

3

16

Δ119868Δ119881(6)










minus6000

minus5000

minus4000

minus3000

minus2000

minus1000

Frequency (GHz)

000

30000 35000 40000 45000 50000 55000 60000

m1 m2

Name33700005911000


m1m2

X Y

dB (S

11)

dB (S11)




11lt






30000 35000 40000 45000 50000 55000 60000Frequency (GHz)

000

2500

5000

7500

10000

12500

15000

Impe

danc

e (O

hm)

Re(Z11)Im(Z11)

m1

m2

Name5000000 2202945000000 798285

m1m2

X Y


000

1000

90

60

30

0

150

120

dB (Gain Total)

dB (Gain Total)

m1

m2

minus2000

minus1000minus60

minus90

minus120

minus150

minus180

900000 95817390000m2

Name Ang Magm1

minus18921



minus30






000 6000 12000 18000

200

1000

1800

dB (D

ir T

otal

)

dB (Dir Total)

Name900000 103790604340 30000

1195567 30000

m1

m1

m2 m2

m3

m3

X Y

minus3000

minus2200

minus1400

minus600


120579 (deg)




RTD1

RTD2

Upper

Upper

Lower

Lower

Electrode

Electrode

MIM reflector

MIM reflectorSI-InP

SiO2

SiO2

Coupling part




1and RTD



120596 = 120596

(119890) and 120596

(119900)

= 120596

1

[

[

radic

1 + (

120596

1119871

2

Im (119884

12))

2

∓

120596

1119871

2

Im (119884

12)

]

]

(7)

where 120596


1is operated


Lower electrodeL5


Lower

w3w3

SiO2


30000 35000 40000 45000 50000 55000 60000Frequency (GHz)

000

dB(S11)dB(S21)

dB(S22)

S-pa

ram

eter

s (dB

)

minus7000

minus6000

minus5000

minus4000

minus3000

minus2000

minus1000








1003816

1003816

1003816

1003816

119883

1+ 119883

2

1003816

1003816

1003816

1003816

2

=


(8)

where 119883


satisfies |119883119899|

2


120581 = minus

119884

12

(119886 minus 119866

119871)

119886 = (

3

2

) (

Δ119868

Δ119881

)

(9)




11and 119878

22are




30000 35000 40000 45000 50000 55000 60000Frequency (GHz)

000000

000005

000010

000015

000020

m1

Namem1

X Y

000015000000

Re(Y12)Im(Y12)

minus000015

minus000010

minus000005

Y12(S)


12


dB (Gain Total)

dB (Gain Total)

minus2000

minus1000

900000

000

1000

90

60

30

0

150

120

m1

m2

121814410000 10954m2

Name Ang Magm1

minus30

minus60

minus90

minus120

minus150minus180











000 6000 12000 18000

200

1000

1800

dB (D

ir T

otal

)

m1

m2 m3

dB (Dir Total)

Name900000 130858589770 30000

1208521 30000

m1m2m3

X Y


minus2200

minus1400

minus600

120579 (deg)




5 Conclusion


21






Acknowledgments


References
































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation












minus6000

minus5000

minus4000

minus3000

minus2000

minus1000

Frequency (GHz)

000

30000 35000 40000 45000 50000 55000 60000

m1 m2

Name33700005911000


m1m2

X Y

dB (S

11)

dB (S11)




11lt






30000 35000 40000 45000 50000 55000 60000Frequency (GHz)

000

2500

5000

7500

10000

12500

15000

Impe

danc

e (O

hm)

Re(Z11)Im(Z11)

m1

m2

Name5000000 2202945000000 798285

m1m2

X Y


000

1000

90

60

30

0

150

120

dB (Gain Total)

dB (Gain Total)

m1

m2

minus2000

minus1000minus60

minus90

minus120

minus150

minus180

900000 95817390000m2

Name Ang Magm1

minus18921



minus30






000 6000 12000 18000

200

1000

1800

dB (D

ir T

otal

)

dB (Dir Total)

Name900000 103790604340 30000

1195567 30000

m1

m1

m2 m2

m3

m3

X Y

minus3000

minus2200

minus1400

minus600


120579 (deg)




RTD1

RTD2

Upper

Upper

Lower

Lower

Electrode

Electrode

MIM reflector

MIM reflectorSI-InP

SiO2

SiO2

Coupling part




1and RTD



120596 = 120596

(119890) and 120596

(119900)

= 120596

1

[

[

radic

1 + (

120596

1119871

2

Im (119884

12))

2

∓

120596

1119871

2

Im (119884

12)

]

]

(7)

where 120596


1is operated


Lower electrodeL5


Lower

w3w3

SiO2


30000 35000 40000 45000 50000 55000 60000Frequency (GHz)

000

dB(S11)dB(S21)

dB(S22)

S-pa

ram

eter

s (dB

)

minus7000

minus6000

minus5000

minus4000

minus3000

minus2000

minus1000








1003816

1003816

1003816

1003816

119883

1+ 119883

2

1003816

1003816

1003816

1003816

2

=


(8)

where 119883


satisfies |119883119899|

2


120581 = minus

119884

12

(119886 minus 119866

119871)

119886 = (

3

2

) (

Δ119868

Δ119881

)

(9)




11and 119878

22are




30000 35000 40000 45000 50000 55000 60000Frequency (GHz)

000000

000005

000010

000015

000020

m1

Namem1

X Y

000015000000

Re(Y12)Im(Y12)

minus000015

minus000010

minus000005

Y12(S)


12


dB (Gain Total)

dB (Gain Total)

minus2000

minus1000

900000

000

1000

90

60

30

0

150

120

m1

m2

121814410000 10954m2

Name Ang Magm1

minus30

minus60

minus90

minus120

minus150minus180











000 6000 12000 18000

200

1000

1800

dB (D

ir T

otal

)

m1

m2 m3

dB (Dir Total)

Name900000 130858589770 30000

1208521 30000

m1m2m3

X Y


minus2200

minus1400

minus600

120579 (deg)




5 Conclusion


21






Acknowledgments


References
































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










000 6000 12000 18000

200

1000

1800

dB (D

ir T

otal

)

dB (Dir Total)

Name900000 103790604340 30000

1195567 30000

m1

m1

m2 m2

m3

m3

X Y

minus3000

minus2200

minus1400

minus600


120579 (deg)




RTD1

RTD2

Upper

Upper

Lower

Lower

Electrode

Electrode

MIM reflector

MIM reflectorSI-InP

SiO2

SiO2

Coupling part




1and RTD



120596 = 120596

(119890) and 120596

(119900)

= 120596

1

[

[

radic

1 + (

120596

1119871

2

Im (119884

12))

2

∓

120596

1119871

2

Im (119884

12)

]

]

(7)

where 120596


1is operated


Lower electrodeL5


Lower

w3w3

SiO2


30000 35000 40000 45000 50000 55000 60000Frequency (GHz)

000

dB(S11)dB(S21)

dB(S22)

S-pa

ram

eter

s (dB

)

minus7000

minus6000

minus5000

minus4000

minus3000

minus2000

minus1000








1003816

1003816

1003816

1003816

119883

1+ 119883

2

1003816

1003816

1003816

1003816

2

=


(8)

where 119883


satisfies |119883119899|

2


120581 = minus

119884

12

(119886 minus 119866

119871)

119886 = (

3

2

) (

Δ119868

Δ119881

)

(9)




11and 119878

22are




30000 35000 40000 45000 50000 55000 60000Frequency (GHz)

000000

000005

000010

000015

000020

m1

Namem1

X Y

000015000000

Re(Y12)Im(Y12)

minus000015

minus000010

minus000005

Y12(S)


12


dB (Gain Total)

dB (Gain Total)

minus2000

minus1000

900000

000

1000

90

60

30

0

150

120

m1

m2

121814410000 10954m2

Name Ang Magm1

minus30

minus60

minus90

minus120

minus150minus180











000 6000 12000 18000

200

1000

1800

dB (D

ir T

otal

)

m1

m2 m3

dB (Dir Total)

Name900000 130858589770 30000

1208521 30000

m1m2m3

X Y


minus2200

minus1400

minus600

120579 (deg)




5 Conclusion


21






Acknowledgments


References
































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










30000 35000 40000 45000 50000 55000 60000Frequency (GHz)

000000

000005

000010

000015

000020

m1

Namem1

X Y

000015000000

Re(Y12)Im(Y12)

minus000015

minus000010

minus000005

Y12(S)


12


dB (Gain Total)

dB (Gain Total)

minus2000

minus1000

900000

000

1000

90

60

30

0

150

120

m1

m2

121814410000 10954m2

Name Ang Magm1

minus30

minus60

minus90

minus120

minus150minus180











000 6000 12000 18000

200

1000

1800

dB (D

ir T

otal

)

m1

m2 m3

dB (Dir Total)

Name900000 130858589770 30000

1208521 30000

m1m2m3

X Y


minus2200

minus1400

minus600

120579 (deg)




5 Conclusion


21






Acknowledgments


References
































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation













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











RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









Documents

Research Article Two-Element Tapered Slot Antenna Array ...downloads.hindawi.com/journals/ijap/2014/847475.pdf · Research Article Two-Element Tapered Slot Antenna Array for Terahertz