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In-situ vehicular antenna integration and design aspects for vehicle-to-vehiclecommunications

Thiel, Andreas; Klemp, Oliver; Paier, Alexander; Bernadó, Laura; Kåredal, Johan; Kwoczek,AndreasPublished in:[Host publication title missing]

2010

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Citation for published version (APA):Thiel, A., Klemp, O., Paier, A., Bernadó, L., Kåredal, J., & Kwoczek, A. (2010). In-situ vehicular antennaintegration and design aspects for vehicle-to-vehicle communications. In [Host publication title missing] (pp. 1-5).IEEE - Institute of Electrical and Electronics Engineers Inc..

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In-Situ Vehicular Antenna Integration and DesignAspects for Vehicle-to-Vehicle CommunicationsAndreas Thiel∗, Oliver Klemp∗, Alexander Paier†, Laura Bernado‡, Johan Karedal§, Andreas Kwoczek¶

∗Delphi Delco Electronics Europe GmbHBad Salzdetfurth, Germany

Contact: {andreas.thiel, oliver.klemp}@delphi.com†Institut fur Nachrichtentechnik und Hochfrequenztechnik, Technische Universitat Wien

Vienna, Austria‡Forschungszentrum Telekommunikation Wien (ftw.)

Vienna, Austria§Department of Electrical and Information Technology, Lund University

Lund, Sweden¶Volkswagen AG

Wolfsburg, Germany

Abstract—Vehicle-to-vehicle (V2V) communications aim toenhance driver safety and traffic efficiency by using the recentlydesignated frequency bands in the 5.9 GHz range in Europe. Dueto the time-frequency selective fading behavior of the vehicularcommunication channel, multi-antenna techniques can provideenhanced link conditions by means of diversity processing. Thispaper highlights the integration of a four-element (N = 4) lineararray antenna into the roof-top compartment of a vehicle to con-duct Multiple-Input Multiple-Output (MIMO) high-resolutionmobile-to-mobile channel measurements.

I. INTRODUCTION

Wireless V2V communication systems are currently beingresearched regarding their potential to reduce traffic congestionand traffic accident rates. An even higher priority of investigat-ing the V2V radio channel in the 5GHz band is caused by therecent allocation of a bandwidth of 30MHz at 5.9GHz whichhas been allocated by the European Commission in August2008. The frequency band from 5875MHz to 5905MHz isespecially intended for safety related intelligent transportationsystems (ITS). The simulation and performance evaluation ofmobile-to-mobile vehicular communication systems dramati-cally depends on the spatiotemporal fading behavior of the un-derlying propagation channels. In contrast to cellular systems,the performance in V2V communications systems is impactedby non-stationary fading conditions of the channel parameters.E. g. [1] and [2] present initial results in the 2.4GHz and5.2GHz domain for V2V- and Vehicle-to-Infrastructure (V2I)channels. [3] provides an overview of recent vehicular channelmeasurement campaigns. Due to the presence of multiplevehicles in heavily loaded V2V communications systems andthe nature of the rapidly varying channel parameters, multipleantenna techniques have gained considerable attention in thefield of V2V communications. Those provide appropriatemeans for flexible network coverage, interference mitigation,

and diversity functionality for safety-related communicationapplications. Based on the experience from a first V2V radiochannel measurement campaign [2] in 2007, we carried outan improved multiple-input multiple-output (MIMO) V2Vchannel measurement campaign in the 5.6GHz domain, calledDRIVEWAY, in June 2009. The difference to the channelmeasurement campaign in 2007 is based on an automotive-grade realization of a MIMO antenna front-end which wenow used for the mobile-to-mobile channel measurements.This paper presents an overview of the design aspects, thevehicular integration and in-situ vehicular measurements ofthe 4-element MIMO antenna module.The paper is structured as follows: Sec. II describes thebaseline of the underlying antenna design whereas III focuseson its vehicular integration. Sec. III-A highlights the resultsfrom an electromagnetic in-situ characterization of the antennamodule on the vehicle and Sec. IV draws a conclusion.

II. ANTENNA MODULE DESIGN ASPECTS

An automotive-grade antenna module including four indi-vidual antenna elements for V2V- /V2I- communications hasbeen developed for a mobile-to-mobile channel measurementcampaign DRIVEWAY in the specific frequency band from5480MHz to 5720MHz. This frequency band limitation isdetermined by the applied RUSK LUND channel sounder thathas been used for this measurement campaign. The measure-ment frequencies are very close to the allocated 5.9GHz fre-quency band for ITS in Europe and we assume the variationsin the conditions of the radio channel to be negligible between5.6GHz and 5.9GHz.A conventional Volkswagen roof-top antenna module wasused as the baseline for the antenna integration. Due to thelimited mounting space inside the module and especiallywith respect to its limited height, the antenna design was

based on a low-profile antenna prototype. With the require-ment of a monopole-like radiation pattern for almost omni-directional, terrestrial coverage, the design is based on acircular patch antenna driven in a higher operational-mode.Feeding concepts and terrestrial operational modes of theintegrated patch antenna element are inline with e. g. [4]. Thetypical antenna layout (top-view and side-view) including anexcentric feeding pin and a centered, metallic post is shownin Fig. 1. The antenna prototype is manufactured on Rohacelldielectric material with a sheet thickness of tPatch = 1mmand a relative permittivity of εr,Patch � 1.0. The outerdiameter of the circular patch and the shorting post amount todPatch = 10.0mm and dsp = 1.0mm. For the arrangement

���������

���������

ϕ

dsp

dPatch

z

x

shorting post

x

feeding pin

y

dielectric

copper layer

tPatch

Fig. 1. Geometry of the circular patch antenna driven in a higher operationalmode with feeding pin and metallic shorting post.

of the four antennas within the roof-top compound, a uniformlinear array (ULA) configuration was chosen. The individualantenna elements within the ULA are separated by λ/2 at5.6GHz in order to reduce impedance-based mutual couplingeffects and to compensate for a deterioration of the antenna ra-diation patterns, mainly in the xy-plane. Fig. 2 depicts a blockdiagram of the ULA including the principal location of V2Vantennas within the roof-top compound. Scattering parametermeasurements of the antenna module were taken when theroof-top module was mounted on a small electric ground plane(GP) featuring a diameter of 200mm. Impedance matching at50Ω provides low values of the associated return loss valuesS1,1 through S4,4 for all antenna elements V2V#1 throughV2V#4 in the order of magnitude of approx. 10 dB within theconsidered frequency band from 5.48GHz to 5.72GHz. Therespective transmission coefficients S21, S32, S43, etc. betweenall four individual antenna elements range below −12 dB in

ϕ

y

x

� 130 mm

�50

mm V

2V#2

V2V

#1

λ/2 λ/2 λ/2

V2V

#4

V2V

#3

feeding pin

Fig. 2. Block diagram of the ULA including N = 4 elementsV2V#1 through V2V#4 with feeding pins and metallic shorting posts. The−y-axis denotes vehicle driving direction.

the entire frequency range of operation. This is considered tobe an acceptable value yielding a sufficient degree of powerdecoupling between all antennas.Calibrated radiation pattern measurements of each individ-ual V2V antenna were taken in a spherical nearfield testchamber at Delphi Delco Electronics Europe GmbH in BadSalzdetfurth, Germany. The ULA itself and, at a later stage,the ULA integrated into the Volkswagen roof-top antennamodule as sketched in Fig.2 were mounted on a sophisticatedcustom-made ground plane with diameter dGP = 1m androlled edges in order to reduce diffraction effects of theelectromagnetic field. The far-field antenna gain patterns ofeach individual antenna element are shown in Fig. 3, whenthe ULA is directly mounted on the GP. Tab. I presents asummary of measured vertical antenna gains including therespective angular positions ϑmax and ϕmax of their obser-vation. As can be seen from Fig. 3, each V2V antenna ischaracterized by an individual beam pattern coverage. Thisbehavior is attributed by mutual coupling effects betweenthe elements. Following Fig. 3(a) and Fig. 3(d), the relevantantenna elements V2V#1 and V2V#4 predominantly cover theleft- and also the right halfspace centered around ϕ = 0◦ andϕ = 180◦ in the azimuth plane. In contrast to this radiationbehavior, the two elements V2V#2 and V2V#3, located in thecenter of the ULA point into the opposite azimuth directionsof ϕ = 90◦ and ϕ = 270◦. The absolute ϕmax-positionsof vertical antenna gain are given in Tab. I. As can be alsoseen from Tab. I, mounting the ULA on a groundplane offinite size leads to a certain beam tilt in elevation ϑ. Withthe circular GP, a distinct beam tilt of ϑmax � 75◦ isobserved for each individual antenna element and is attributedby a respective reduction of directive antenna gain in the xy-plane. The elements V2V#1 and V2V#2 are characterized byalmost identical antenna gain values of GV2V#1 = 7.1 dBiland GV2V#1 = 7.5 dBil. V2V#3 and V2V#4 exhibit lowerantenna gains of GV2V#1 = 5.7 dBil and GV2V#1 = 4.8 dBil.

III. VEHICULAR INTEGRATION

Since the DRIVEWAY measurement campaign focuses onthe characterization of the vehicular communication channelwith application-specific antenna equipment, the integrationof the ULA is based on an antenna module that is ready for

0◦

ϕ = 90◦

30 ◦

60 ◦

ϑ=

90 ◦

vertical gain / dBil

-15 -10 -5 0 4 8

(a) Antenna V2V#1

0◦

ϕ = 90◦

30 ◦

60 ◦

ϑ=

90 ◦

vertical gain / dBil

-15 -10 -5 0 4 8

(b) Antenna V2V#2

0◦

ϕ = 90◦

30 ◦

60 ◦

ϑ=

90 ◦

vertical gain / dBil

-15 -10 -5 0 4 8

(c) Antenna V2V#3

0◦

ϕ = 90◦

30 ◦

60 ◦

ϑ=

90 ◦

vertical gain / dBil

-15 -10 -5 0 4 8

(d) Antenna V2V#4

Fig. 3. ULA mounted directly on GP, calibrated far-field antenna gain patternV2V#1 to V2V#4.

TABLE IANTENNA GAIN SUMMARY FOR ELEMENTS V2V#1 TO V2V#4 IF THE

ULA IS DIRECTLY MOUNTED TO THE GP.

Antenna element # G / dBil ϑmax / ◦ ϕmax / ◦V2V#1 7.1 75 50V2V#2 7.5 75 95V2V#3 5.7 75 280V2V#4 4.8 75 95

series production and which is located at a realistic mountingposition on the vehicle. From the perspective of an automotive-compliant antenna integration, a relevant position for V2Vantenna equipage is determined by the usual roof-top antennamodule. This one is centered and -located at the back of themetallic vehicle roof. Usually, the roof-top antenna moduleprovides functionality for a couple of different broadcastingand telecommunications services. Those typically include an-tennas for cellular communications, and Global PositioningSystem (GPS), and additional service coverage that interactwith the V2V antenna front-end [5]. Fig. 4 shows the Volk-

swagen Touran measurement vehicles that were used withinthe DRIVEWAY measurement campaign. Each vehicle (one isused as a transmitter (TX), the other one is used as a receiver(RX)) is equipped as indicated with an identical antenna front-end which is installed on the conventional mounting positionfor roof-top antennas. Clearly, integrating the ULAs into the

RX vehicle TX vehicle

measurement range

roof−top antenna

Fig. 4. TX- and RX measurement vehicles in front of the in-situ vehicularmeasurement facility.

roof-top antenna module causes a significant impact on theantenna radiation patterns. The applied die-cast as well as theshape of the printed circuit board and the dielectric designcover of the roof-top module lead to a significant deteriorationof the related antenna far-field gain patterns. In addition tothose more near-field related effects, it is also the vehicle-specific roof-top dimensions that impact on the performanceof the antennas. In order to keep control of the individualdegradations of the radiation behavior, M = 6 parasitic wireelements were integrated into the roof-top module, addition-ally. The geometrical length of those passive elements waschosen to be approximately λ/4 at 5.6GHz in a way that theyare able to scatter electromagnetic energy. The elements wereshort circuited in their respective root-points such that they actas discrete scatterers in the antenna compartment, directingelectromagnetic energy into a predestined angular direction.Depending on the electrical length and distance relative tothe four actively-fed antennas within the ULA, those elementscan be effectively applied to achieve a distinct - but limited- degree of beam shaping. Fig. 5 depicts the location of thepassive directors relative to the N = 4 individual antennaelements of the ULA in the xy-plane.

λ/2

ϕx

� 130 mm

�50

mm

parasitics

feeding pin

V2V

#4

V2V

#1

λ/4

y

Fig. 5. Block diagram of the ULA including M = 6 parasitics for beamshaping.

The calibrated and measured far-field antenna gain pat-

terns for the N = 4 individual antennas V2V#1 throughV2V#4 within the ULA given in Fig. 5 are shown in Fig. 6.Tab. II includes a gain summary for the ULA configuration

0◦

ϕ = 90◦

30 ◦

60 ◦

ϑ=

90 ◦

vertical gain / dBil

-15 -10 -5 0 4 8

(a) Antenna V2V#1

0◦

ϕ = 90◦

30 ◦

60 ◦

ϑ=

90 ◦

vertical gain / dBil

-15 -10 -5 0 4 8

(b) Antenna V2V#2

0◦

ϕ = 90◦

30 ◦

60 ◦

ϑ=

90 ◦

vertical gain / dBil

-15 -10 -5 0 4 8

(c) Antenna V2V#3

0◦

ϕ = 90◦

30 ◦

60 ◦

ϑ=

90 ◦

vertical gain / dBil

-15 -10 -5 0 4 8

(d) Antenna V2V#4

Fig. 6. ULA integrated into VW rooftop module, calibrated far-field antennagain patterns V2V#1 to V2V#4.

which is embedded in the roof-top antenna module. Dueto the mounting position on a rolled-edge ground planeof finite size, a distinct beam tilt towards ϑmax � 75◦

is observed. As a consequence from the dielectric loadingeffects of the roof-top antenna cover, the integration of theULA into the die-cast and the additional mounting of theaforementioned M = 6 parasitics, the values of antenna gaindiffer from the results as indicated in Tab. I for the ULAitself. V2V#1 to V2V#3 provide almost identical antennagain yielding GV2V#1 = 9.1 dBil, GV2V#2 = 9.6 dBil andGV2V#3 = 9.5 dBil, respectively. The azimuthal positions ofmaximum antenna gain are observed at ϕmax,V2V#1 = 5◦,ϕmax,V2V#2 = 75◦ and ϕmax,V2V#3 = 235◦. V2V#4 exhibitsa reduced antenna gain of GV2V#4 = 7.8 dBil which isobserved at ϑmax = 75◦ and ϕmax = 130◦. This gainreduction can also be derived from Fig. 6(d) that clearlyindicates a more uniform gain distribution for V2V#4 in the

azimuth plane ϕ centered around ϑmax � 75◦.

TABLE IIGAIN SUMMARY FOR ELEMENTS V2V#1 TO V2V#4 IF THE ULA IS

INTEGRATED INTO THE ROOF-TOP ANTENNA MODULE.

Antenna element # G / dBil ϑmax / ◦ ϕmax / ◦V2V#1 9.1 75 5V2V#2 9.6 75 75V2V#3 9.5 75 235V2V#4 7.8 75 130

A. Results

Following the presented measurements of the ULA locatedon a GP with diameter dGP = 1m and rolled edges as inthe preceding Section II and for the modified module as inSection III , this section highlights the effects of realisticvehicular antenna integration and presents measurement resultson vehicle level. This implies integrating the ULA into theautomotive antenna module as depicted in Fig. 2 and mountingthe module on the vehicle roof-top as shown on Fig. 4.The ULAs as described in Sec. III are integrated into the roof-top modules and placed on the back of the roof-top of theTX- and RX car as shown in Fig. 4. The Volkswagen antennahousings are oriented perpendicular to driving direction ina way that the ULA is also oriented perpendicular to thedriving direction. Considering the antenna positions as shownin Fig. 5, antenna element V2V#1 is oriented to the left of themeasurement vehicle and antenna element V2V#4 is orientedto the right. Both directions are defined with respect to thedriving direction of the vehicle that is assumed along the −y-axis as depicted in Fig. 5.Calibrated radiation pattern measurements of the V2V an-tenna modules mounted on the measurement vehicles weretaken in an automated 3D nearfield measurement facility atDelphi Delco Electronics Europe GmbH in Bad Salzdetfurth,Germany. The vehicle was placed on a conductive turntable(diameter d = 6m) which is embedded in a circular con-ductive floor with d = 24m in diameter. Fig. 7 depicts thecalibrated far-field antenna gain patterns of the individualelements V2V#1 to V2V#4. Tab. III includes a summary ofantenna gains for the in-situ vehicular antenna measurements.Following the design flow as described in Sec. III, the M = 6passive wire elements effectively improve the shape of therelated antenna beam patterns. Element V2V#1 which is

TABLE IIIGAIN SUMMARY FOR CALIBRATED IN-SITU VEHICULAR MEASUREMENTS

OF V2V#1 THROUGH V2V#4 .

Antenna element # G / dBil ϑmax / ◦ ϕmax / ◦V2V#1 7.8 75 10V2V#2 6.8 80 100V2V#3 7.5 80 280V2V#4 3.4 75 165

pointing at ϑmax = 75◦, ϕmax = 10◦ comprises a directivegain in the order of magnitude of GV2V#1 = 7.8 dBil for the

0◦

ϕ = 90◦

30 ◦

60 ◦

ϑ=

90 ◦

vertical gain / dBil

-15 -10 -5 0 4 8

(a) Antenna V2V#1

0◦

ϕ = 90◦

30 ◦

60 ◦

ϑ=

90 ◦

vertical gain / dBil

-15 -10 -5 0 4 8

(b) Antenna V2V#2

0◦

ϕ = 90◦

30 ◦

60 ◦

ϑ=

90 ◦

vertical gain / dBil

-15 -10 -5 0 4 8

(c) Antenna V2V#3

0◦

ϕ = 90◦

30 ◦

60 ◦

ϑ=

90 ◦

vertical gain / dBil

-15 -10 -5 0 4 8

(d) Antenna V2V#4

Fig. 7. In-situ vehicle measurement results, calibrated far-field antenna gainpatterns V2V#1 to V2V#4.

vertical component of the antenna far-field. The vertical far-field gain of V2V#4 amounts to GV2V#4 = 3.4 dBil and isobserved at ϑmax = 75◦, ϕmax = 165◦. The antenna elementsV2V#2 and V2V#3 that are located close to the center of theULA provide vertical antenna gains of GV2V#2 = 6.8 dBiland GV2V#3 = 7.5 dBil. The latter two antennas are bothpointing bi-directional into the half-spaces centered aroundϕ = 90◦ and ϕ = 270◦. V2V#2 provides its maximum gainat ϑmax = 80◦, ϕmax = 100◦ whereas V2V#3 is pointing toϑmax = 80◦, ϑmax = 280◦. The slightly increased beam tiltof ϑmax = 80◦ for V2V#2 and V2V#3 is attributed by thedistinct roof-top curvature of the measurement vehicles.

IV. CONCLUSION

This paper focuses on the design of an automotive-gradefour-element (N = 4) uniform linear antenna (ULA) arraywhich is integrated into a realistic roof-top antenna module fora high-resolution vehicle-to-vehicle measurement campaign.The antenna elements are based on the concept of a circularpatch which is driven in a higher operational mode, thus

leading a terrestrial radiation pattern. M = 6 passive andresonant metallic wire elements were integrated into the roof-top module in order to compensate for mutual-coupling baseddeteriorations of the antenna radiation patterns and vehicularintegration effects. Calibrated radiation pattern measurementswere taken for the ULA on module level in a spherical near-field test chamber as well as on the vehicle level in a vehicularin-situ measurement facility.

REFERENCES

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[2] A. Paier, J. Karedal, N. Czink, H. Hofstetter, C. Dumard, T. Zemen,F. Tufvesson, A. F. Molisch, and C. F. Mecklenbrauker, “Car-to-Car RadioChannel Measurements at 5 GHz: Pathloss, Power-Delay Profile, andDelay-Doppler Spectrum,” Proceedings of the 4th IEEE InternationalSymposium on Wireless Communication Systems, vol. 1, pp. 224–228,17-19 October 2007.

[3] A. F. Molisch, F. Tufvesson, J. Karedal, and C. F. Mecklenbrauker, “Prop-agation aspects of vehicle-to-vehicle communications - an overview,”Proceedings of the 2009 IEEE Radio and Wireless Symposium, vol. 1,pp. 179–182, 18-20 January 2009.

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