Benjillali, Mustapha

Fady, Brahim

Joseph, Wout

Martens, Luc

Tanghe, Emmeric

Tribak, Abdelwahed

Vermeeren, Günter

English

Ghent University Academic Bibliography

1Miniaturized 2.4 GHz Antenna and Path LossInvestigations for Metal Containers MonitoringBrahim Fady, Gunter Vermeeren, Wout Joseph, Senior Member, IEEE, Mustapha Benjillali, Senior Member, IEEE,Abdelwahed Tribak, Member, IEEE, Emmeric Tanghe, Luc Martens, Member, IEEEAbstract—This paper presents a future terminal antenna to en-hance the performance of wireless container monitoring systems.It first introduces an optimized design that is experimentallyvalidated for Wireless Personal Area Network (WPAN) technol-ogy taking into account the harsh environment of containers.The proposed antenna exhibits excellent performance next to thecontainer in terms of return loss, gain, and bandwidth. Further,deterministic and stochastic path loss models for inter-containerlink budget calculations are used to illustrate the impact of theoptimized antenna on path loss and attainable maximum ranges.Index Terms—Container, path loss, link budget, optimizedantenna, ISM band, Internet of things.I. INTRODUCTIONThe evolving trend in industry chain process is to improvedistribution services. Sensor networks, low-power micro-controllers and optimized antennas are increasingly used insupply chain. The clients need accurate information (e.g,location, arriving time, temperature) on the whereabouts oftheir containers, anywhere enroute to ensure the integrity andthe security of the transported goods. The port and the shippresents difficult radio frequency issues (attenuation, reflexion,interference) caused by the metallic structure of the containerwhich impacts the antenna reflection, gain and propagation(e.g., shielding and interference of signals [1]). However, thecommunication still can be improved using optimal antennas.Path loss models for container environments have beenproposed in [1] and [2], but they are based on non-optimizedantennas next containers. Propagation for container environ-ments has been investigated scarcely up to now. Based on mea-surements, path models in a container terminal are proposedfor the frequency band [1 GHz, 4 GHz] using different antennaheights [2]. In [1], intra- and inter-container path loss forshipping container monitoring systems is investigated for IEEE802.15.4 (433, 868, and 2400 MHz) and extra-container pathloss is examined at GSM/UMTS (900, 1850, and 2100 MHz).The iMinds-COMACOD project is co-funded by iMinds, a research institutefounded by the Flemish Government and Companies. This research is alsopartly funded by the Fund for Scientific Research - Flanders (FWO-V,Belgium) project G.0325.11N. W. Joseph and E. Tanghe are Post-DoctoralFellow of the FWO-V (Research Foundation - Flanders).B. Fady, G. Vermeeren, W. Joseph, E. Tanghe, L. Martens are with iMinds-INTEC-Ugent (Department of Information Technology - Ghent University),Gaston Crommenlaan 8 box 201, B-9050 Ghent, Belgium.M. Benjillali is with the Communication Systems Department, INPT, Rabat,Morocco.A. Tribak is with the Microwave and Communication Antenna SubsystemsDepartment, INPT, Rabat, Morocco.E-mail: Wout.joseph@intec.ugent.beThe objective is to design an optimal antenna attached toa metal container for operation in the 2.4 GHz industrial,scientific and medical (ISM) wireless communication band.Based on the proposed design, the link budget is considerablyimproved. This will enable connecting containers to the inter-net and reducing the costs of containers monitoring systems.II. PROPOSED ANTENNA DESIGNA. Optimization SetupWe started from a planar off-the-shelf antenna (RHEA dualband antenna 2.4 GHz/5.8 GHz), in order to obtain a low-costantenna (q.v Figure 2). The substrate of the RHEA antennasizes 50x16x1 mm3 and modeled as a dielectric with a relativepermittivity εr = 5. The dipole is fed asymmetrically withone arm sized 2x21 mm2 and the other 2x22 mm2. Botharms are modeled as perfect electric conductors (PECs). Weoptimized this antenna near the container, modeled as PEC andsized 2377x5682x2377 mm3, using the full genetic algorithm(GA) optimization routine on top of the 3D finite-differencetime-domain (FDTD) method as implemented in the softwareplatform SEMCAD-X (SPEAG, Zurich, Switzerland).Figure 1 shows the antenna mounted on the inner rail ofthe container. The antenna is placed at 23 mm from the metalsurface of the container. For safety reasons, and to avoidvandalism, the antenna is located inside the housing of thecircuitry, called the air-ventilator box. Besides the antenna,the air-ventilator box contains two printed circuit boards(PCBs), a GPS and a GPRS/GSM board. Each board measures38x75x1.6 mm3 and modeled as PEC. The GPRS/GSM boarddenoted as ”Bottom PCB” is placed at the bottom of the air-ventilator whereas the GPS Board, denoted as ”Top PCB”, isplaced on top of the GPRS/GSM board with a separation of4 mm.The parameters of the optimization are the length of thedipole arms, the width of the arms and the separation (stepof 2 mm) between the antenna and the container surface. Inthe optimization process, we took into account the containeras well as the PCBs and the ventilator box.B. Final DesignFigure 2 shows the manufactured design, tuned taking intoaccount the estimated relative permittivity of the substrate, theholder and the cover. The resulting dimensions of the planardipole are 22x2 mm2 for each arm. The gap between the armsis 1 mm. The substrate made of FR4 material has a relativepermittivity of 4.4, and sizes 8x53x0.8 mm3. The solderingspaces are modeled as PEC surfaces sizing 2x4 mm.2Figure 1. Configuration of the antenna on the container. A: antenna placedupside-down, B: Top PCB and Bottom PCB, C: inner rail of container, D:air-ventilator box, E: a part of the container.Figure 2. The final design tuned near container.C. Measurement and Simulation Results1) Comparison in Free Space : Figure 3 describes andcompares the results of simulations to measurements in freespace in terms of S11 with respect to 50 Ω. We observe that infree space, the measurements correspond to simulations witha small offset in the resonant frequency up to 0.1 GHz. Wenote also that the bandwidth measured is 0.2 GHz less thansimulation results.2) Next to Metal Plate: Figure 4 shows the measuredS11 near a metal plate. We observe that both simulatedand measured S11 cover the ISM radio band at 2.4 GHz.The measurements show that the bandwidth increases withdecreasing width of the dipole arms. We have to remark thatthe measurements were performed in our testlab where fadingcould not be avoided. Figure 4 also shows that the optimizedantennas performs up to 15 dB better in terms of S11 in the2.4 GHz band compared with the off-the-shelf antenna (RHEAdual band antenna 2.4 GHz/5.8 GHz), which is clearly detuned(to 2.15 GHz) when operated next to the metal plate.Figure 3. Free space comparison between simulation and measurements ofthe S11 parameter.Figure 4. S11 measurements on a metal plate and influence of the width ofthe dipole arms on the reflection.3) Antenna Mounted on The Container: Finally, we alsomeasured reflection and transmission of the optimized antennaon the container. Figure 6 shows the measured reflection ona container. Both dipole antennas cover the ISM band at2.4 GHz.4) Estimation of The Relative Permittivity of The Substrate,Holder and Cover: The dielectric properties of the plastics ofthe cover and the holder were unknown in advance, whereaswe selected for the substrate of the antenna a typical value ofFR4 εr = 4.9.To estimate the relative permittivity of the holder, wemeasured on a metal plate in our testlab, the reflection ofthe antenna mounted on the holder as shown in Figure 7 (b),and compared it with simulations (same configuration) whilevarying the relative permittivity of the holder in simulations(cf. Figure 8). We obtained a resonance frequency same as themeasurement for εr = 1.5. In the same way we evaluated therelative permittivity of the cover. The configuration is shownin Figure 7 (a), the antenna is mounted on the holder andceiled with the cover. The simulations fit to measurements, interm of resonance frequency, for εr = 1.8.3Figure 5. Metal impact on the RHEA antenna reflection at 2.4 GHz.Figure 6. S11 of the optimized antennas on the container.5) Investigating the Influence of External Factors on TheAntenna: Figure 8 shows the influence of the holder and thecover on S11, and compares it with the simulation results.The measured S11 of the antenna attached to the holder onthe metal plate, Figure 7 (a), shows a resonance frequency of2.95 GHz, but the simulated S11, with the same configurationwith selected permittivity, resonate at 2.7 GHz. In the samefigure, we observe that when adding the cover, the measuredS11 of the antenna resonates at 2.7 GHz, otherwise the S11simulation result, using the selected permittivities, resonate at2.4 GHz. This comparison allowed us to estimate the relativepermittivity of the holder and the cover (q.v in the previoussubsection).6) Investigating the Influence of the PCBs: After investi-gating the influence of the cover, we shed light in this part onthe influence of the PCBs. The lower PCB is located at thesurface of the metal plate (inner rail of the container), thus ithas no additional effect on the antenna besides the influenceof metal plate in terms of reflection. Hence, we describe inthis part only the influence of the Top PCB, which is 5.6 mmseparated from the surface of the inner rail.The Figure 9 shows a comparison between the S11 result ofthe model without the top PCB and the result when includingthe Top PCB Module. We observe that in the absence of thetop PCB, the antenna radiates in the ISM band at 2.4 GHz witha S11 up to -30 dB. On the other hand, when adding the topPCB, the value of resonance frequency nearby changes (a shiftof 0.2 MHz), otherwise the reflection coefficient increases to -14 dB. This means that the top PCB degrades the quality of theantenna (increases the reflection) and makes the optimizationof the new design more difficult.III. CHANNEL MODEL AND LINK BUDGETAfter designing an optimized antenna near container ac-counting for external factors, we characterize in this sectionthe path loss in order to provide a channel model that can beused, for further research, in a container environment. FinallyFigure 7. Influence of the holder and the cover of the Track4C node on thereflection of the planar dipole antennaFigure 8. (a) : Antenna attached to the holder. (b) : The antenna is ceiledwith cover of the air-ventilator.we will calculate the coverage range,based on the link budget,of the tuned antenna.A. Path Loss1) Excluding Antenna Gain: Path loss (PL) is the reductionin power density of the transmitted signal (wave) [8]. Path lossPL is used for the link budget calculations of a telecommuni-cation system. The power at the receiver input terminals, Pr,can be expressed as :Pr =PtGrGtPLLtLr⇒ PL =PtGrGtPrLtLr(1)Where Pr is the received power and Pt is the emittedpower. Gt, Gr are the gains of the receiver and the transmitterantennas, respectively. Lt,Lr are feeders losses.2) Including Antenna Gain: Similarly to a Wireless BodyArea Network (WBAN), where the human body affects theantenna radiation pattern, the metallic structure of the con-tainer makes the dipole antenna not omnidirective. Thereby,the antenna effect cannot be removed from the propagationpath loss [1][7]. By this way, the path loss used in WBANstudies PLincl includes the antenna effect and differs thusfrom PL:PLincl =PLLtLrGrGt=PtPr(2)Henceforth, we refer by path loss to PLincl.4Figure 9. S11 result and comparison between Top PCB included and notincludedB. Propagation Result of The Optimized DesignWe investigate in this part the transmission in terms of S21along a metal plate and a container using the optimized design.First, we compare the measurements to simulations of thepropagation, and we end comparing the non-optimized designwith tuned design in terms of transmission.The measurement of the path loss, in terms of the scatteringparameter S21, along a single container consisted of theantenna placed on the holder which was attached to the innerrail of the container (Figure 10). The transmitter and thereceiver antennas were both connected to the vector networkanalyzer (VNA) which is a Rohde Schwarz ZNB20. Duringthese measurements, we had to remove the cover to be ableto connect the antenna to the VNA.Figure 10. configuration of the S21 measurement on the containerFigure 11 shows the S21 measurements performed on thecontainer. We selected the two antennas with the best S11performance on the container. We placed the Tx antenna inthe second inner rail of the container, and we moved the Rxantenna through the rest of inner rails of the container. InFigure 11, we observe that the S21 result of the measurement ismuch better than the simulation result where the S21 decreasesswiftly and monotonically. This is due to the absence of themultipath effect in the simulation compared to the environmentof measurements where the multipath is ensured by the objectaround the container. With respect to the simulation result thefluctuations are not prominent but the S21 decreases rapidly.We observe that the measured S21 decreases slowly but under-goes fluctuations. One of the main reasons of these fluctuationsis the obstruction caused by the rails of the container. For bothsimulation and measurement we can notice the influence of thecontainer which degrades the propagation performance of theantenna (decreasing the S21 and shadowing effect).Figure 11. The measured S21 along a single container using the optimizedantenna.Figure 12. Comparison of measured PL on the container between the non-optimized antenna and the final design.Figure 12 compares the non-optimized design(RHEA an-tenna) and the final design in term of measured transmission(path loss) between two nodes along the container for aseparation step of up to 280 mm. For both designs, we clearlyobserve the fading of the environment resulting in a non-monotonic decrease of S21 with separation between the twonodes. For a distance lower than 4 meters, the RHEA designexhibits better transmission (about 6 dB in average) than the5optimized antennas (optimized design). However, the path lossexpressed by the first run design increases rapidly (alreadyup 60 dB at 4 m) for separations (between transmitter andreceiver) higher than 4 meters.C. Link Budget1) General: The container path loss model [1] consist of apower decreasing term and of two stochastic terms.PLincl = b0 + b1d+ χs + χf (3)Where b0 and b1 are regression parameters from the deter-ministic part of the model and (χs,χf ) represent the stochasticpart. The random variable χs expresses the random fluctua-tions of path loss originating from the shadowing of physicalobjects in the wireless channel (called shadow fading). Therandom variable χf , so-called fast fading margin, results fromthe random fluctuations of the path loss due to changes overtime in the layout of the container channel. The measurementstep was higher than the wavelength, thus we will not accountfor the fast fading margin in the link budget calculation(χf = 0dB).2) Calculation of Regression Parameters and Shadow Fad-ing Margin: To calculate the shadow fading margin, weconsider a 2.4 GHz WPAN system for communication betweencontainers [2], Data transmission rates vary around 250 kilo-bits/second in the 2.4 GHz frequency band. WPAN nodes cansleep most of the time, thus the average power consumptioncan be low. Transmission distances range from 10 to 100 mline-of-sight, depending on power output and environmentalcharacteristics. The system sensitivity is -108 dBm with amaximum transmission power of up to 24 dBm. As discussedbefore, the measurements were carried on the container usingidentical antennas (optimized design), cf. Figure 10. Thetransmitter is placed inside the air-ventilation box and thereceivers are moved in steps of 282 mm along the inner-rails of the container. Based on sample data resulting in 16records, and thus considering that the random data fluctuationis T-distributed, the shadowing margin calculated at the 95%confidence bounds is 3.02 dB.3) Calculation of Maximum Range: In this part, we inves-tigate the attainable range for the tuned antenna and compareit to the attainable range allowed by the first run design (nottuned). The tracking devices/sensors, used for containers mon-itoring, have minimum accepted received power of −94 dBmat 2.4 GHz. The extracted gain of the first run antenna at thedirection of measurement is 1.2 dBi, and it is of up to 2 dBi forthe design. Taking into account the fade margin (2.45 dB), weextract the maximum range using the following link budget:PL = b0 + b1d+ χs + χf ≤ PLmax, PLmax = 94 dB. (4)In Table 1 we compare the maximum ranges of the non-optimized and the optimized design. The maximum range ofthe optimized design is 30 m higher than the non-optimizeddesign. This enables us to obtain larger ranges and thus lessdevices are needed; resulting in a reduced cost (accounting formillions of container).Terminal antenna freq. [GHz] Gain [dBi] Max. Range [m]Non-optimized antenna 2.4 2 11Optimized antenna 2.4 11 41Table IMAXIMUM RANGE COMPARISON BETWEEN THE NON-OPTIMIZED DESIGNAND THE OPTIMIZED ANTENNAIV. CONCLUSIONSIn this paper, we have designed an optimal WPAN antennanext to the metal container that takes into account the impact ofthe ventilator box, the tracking circuit, and the feeding cable.We investigated the most adequate orientation and position inwhich the antenna can be deployed. The optimized model,with a return loss equal to -22 dB and a gain of up to11 dBi, produces a path loss of up to 18 dB lower thanfor non-optimized design. The ranges increase from 18 m to41 m using the optimized system, which reduces the cost ofdeployment.REFERENCES[1] E. Tanghe, W. Joseph, P. Ruckebusch, L. Martens, and I. Moerman,”Intra-, Inter-, and Extra-Container Path Loss for Shipping ContainerMonitoring Systems”, IEEE Antennas and Wireless Propag. Letters, Vol.11, 2012, pp 2–3.[2] R. J. Katulski, J. Sadowski, and J. Stefanski, ”Propagation path lossmodeling in container terminal environment”. in Proc. 68th IEEE Veh.Technol. Conf. (VTC-Fall), Calgary, AB, Canada, Sep. 2008, pp 1–4.[3] S. J. Ambroziak, R. J. Katulski, ”On the usefulness of selected radiowaves propagation models for designing mobile wireless systems incontainer terminal environment”, in Proc 30th URSI Gen. Assembly Sci.Symp., Istanbul, Turkey, Aug. 2011, pp. 3–4.[4] F. Molisch, ”Ultrawideband Propagation Channels-Theory, Measure-ment, and Modeling”, IEEE Trans. on Vehi. Tech., vol. 54, September2005, pp 1–5[5] C. Xiaohua and X. Hanbin, ”Propagation prediction model and per-formance analysis of RFID system under metallic container productioncircumstance”, Microelectron. J., vol. 42, pp 247–252, 2011.[6] A. Balanis, ”Advanced engineering electromagnetics”, John WileyMonth Sons, Inc., New York, 1989.[7] Parini, M. R. Kamarudin, T. Z. Salim, D. T. M. Hee, R. Dubrovka, A.S. Owadally, W. Song, A. Serra, P. Nepa, M. Gallo, and M. Bozzetti,”Antennas and propagation for on-body communication systems” IEEE,Antennas Propag. Mag., vol. 49, no. 3, pp 41–58, Jun. 2007.[8] S. Stavrou, S. Saunders, ”Factors influencing outdoor to indoor radiowave propagation” in Proc. 12th Int. Conf. Antennas Propag., London,U.K., Mar. 2003, pp 581–585.

Miniaturized 2.4 GHz antenna and path loss investigations for metal containers monitoring

Miniaturized 2.4 GHz antenna and path loss investigations for metal containers monitoring

Abstract

Similar works

Full text

Available Versions

Ghent University Academic Bibliography

Crossref