Optimal Design of Smart Mobile Terminal Antennas for Wireless Communication and Computing Systems

Transcription

1 Optimal Design of Smat Mobile Teminal Antennas fo Wieless Communication and Computing Systems Autho Lu, Junwei, Yang, Shiyou Published 2007 Confeence Title th Intenational Symposium on Electomagnetic Compatibility : Poceeding DOI Copyight Statement 2007 IEEE. Pesonal use of this mateial is pemitted. Howeve, pemission to epint/ epublish this mateial fo advetising o pomotional puposes o fo ceating new collective woks fo esale o edistibution to seves o lists, o to euse any copyighted component of this wok in othe woks must be obtained fom the IEEE. Downloaded fom Giffith Reseach Online

2 Optimal Design of Smat Mobile Teminal Antennas fo Wieless Communication and Computing Systems Junwei Lu and *Shiyou Yang Giffith School of Engineeing, Giffith Univesity, Qld 4111, Austalia * College of Electical Engineeing, Zhejiang Univesity, Zhejiang, P.R.China Abstact The pape pesents an electonically beam switched smat mobile teminal antenna (SMTA) aay used in wieless netwok. SMTA aays wee optimized fo the secued communication pefomance and desied adiation coveage. The adiation beam patten towad desied diection is contolled by switched beam contol algoithm. Fou diffeent configuations of SMTA aays and thei design consideations ae discussed in this pape. wieless communication and computing systems, whee the switched beam only coves the desied diection and aea. Smat Mobile Teminal Antenna, Wieless Communications, Wieless Netwok. I. Intoduction Mobile wieless computing netwok has become a significant aea of gowth ecently. The technology of smat o adaptive antennas fo base station of mobile communications has eceived enomous inteests woldwide in ecent yeas. Howeve, the application of smat antennas fo mobile wieless computing teminals and hand-held mobile devices has eceived little attention due to the smat mobile teminal antenna not being available. The main eason is that the physical size of taditional smat antennas based on linea antenna aay with ½ wavelength sepaation in space is too lage to fit into any mobile wieless computing teminal and handheld mobile equipment. Theefoe, the smat mobile teminal antennas with small size ae despeately needed by wieless communications systems. This pape mainly discusses the seven elements based electonically beam switched antenna aays and its optimal design, and application in wieless communications and computing systems. (a) (b) II. Smat Mobile Teminal Antennas (SMTAs) Unlike taditional antennas, such as omnidiectional and diectional patch antennas applied to cuent wieless communication and computing systems, the poposed SMTA aays using switched beam o adaptive beam-foming technologies can significantly incease the secuity level in wieless netwok [1]. Figue 1 (a) (c) illustates the application of SMTAs in /07/$ IEEE (c ) Fig. 1. SMTA used in wieless communication and computing system, (a) Ceiling mounting SMTA, (b) SMTA fo Desktop o notebook computes in BSS mode, (c) SMTA fo wieless netwok in Ad-Hoc mode.

3 III. Design Consideation of SMTA As mentioned in the above section, the SMTA is not a taditional phase aay antenna, all paasitic element woking togethe with souce element fo a diectional beam. Theefoe the optimal design is necessay duing the antenna design. In this point of view, the antenna configuations as studied in this and the next sections ae all optimized by using a GA algoithm with espect to the following goals: the antenna size, eflection coefficient, and beam bandwidth should be as small as possible; and the antenna gain should be as lage as possible. Moeove, othe consideations about thee basic antenna configuations ae discussed as follows. A. Wie SMTA Figue 2 shows the configuation of wie SMTA which consists of seven elements, gound plan and skit. The cental element is a diven element (No.0) connected to RF souce and othe six elements ae paasitic elements (No.1-6) connected to beam contol cicuit. Unlike the taditional linea antenna aays that have to keep sepaation, the monopole antenna aay based wie SMTA has the element sepaation aound to each othe [2]. The othe majo diffeence compaed with the taditional smat antenna aays is that a wie SMTA only equies a single RF souce. shown in Fig. 3, the wavelength will be 0 / and the eduction facto F fo the height of antenna elements will be expessed as F. Futhe size eduction based on optimised design techniques was achieved by embedding an aay of wie monopoles in a dielectic mateial [3]. Fig. 3. Seven elements based dielectic embedded SMTA. C. Patch SMTA The newly developed electonically beam steeable micostip patch SMTA, as shown in Fig. 4, can be mounted in ceilings fo indoo wieless netwok applications [4]. The cental element is fed by two othogonal feed points with a 90 phase diffeence to geneate left-hand cicula polaization of the cuent distibution. Thus the beam-steeing can be caied out equally though six diections in azimuth. Beamsteeing is achieved by eithe open-cicuiting o shotcicuiting the paasitic antenna elements by switches o eactive loads whee an open-cicuited element acts as diecto while a shot-cicuited element effectively becomes tanspaent. The fields geneated by each element couple togethe to fomulate the total fa field. Due to the induced cicula-polaized cuents in the paasitic elements, two shot-cicuited points ae equied fo each element to effectively teminate any cuent pesence. Fig. 2. Configuation of a seven element based wie SMTA. B. Dielectic Embedded SMTA In mobile teminals the size of antenna is an impotant issue as the potability is always a key equiement. Phased aay antennas equie an inteelement spacing of geate than In wie SMTA, the sepaation distance can be educed to Despite this, antennas designed fo the IEEE standad and Bluetooth at 2.4 GHz ae still consideed too lage to be integated into the compute and potable devices. If the antenna elements ae embedded in the high dielectic medium (non-magnetic mateial) as 1.02 #5 #4 #6 #0 #3 #1 #2 PCB ( a ) Hexagonal patch SMTA

4 0.96 B. Results of Dielectic Embedded SMTA #6 #5 #0 #4 #3 The simulation esults compaed with measued esults fo an optimized dielectic embedded SMTA ae shown in Fig. 7 and Fig. 8. #1 #2 PCB (b) Cicula patch SMTA Fig. 4. Seven elements based Patch SMTAs. IV. Simulation and Expeiment Results A. Results of Wie SMTA As explained peciously, the Wie SMTA was designed and optimized by using a GA in which the FEM based full wave simulato, HFSS in fequency domain, is used. Figue 5 and Figue 6 show the eflection coefficient and adiation patten of Wie SMTA at opeating fequency espectively. Fig. 7. Measued eflection coefficient S 11 fo a 7-Element Dielectic Embedded SMTA, measued (solid line); simulated (dot line). Fig. 5. Measued eflection coefficient S 11 fo a 7-Element Wie SMTA. Fig. 6. Measued H-Plane adiation patten fo a 7-Element Wie SMTA at 2.3GHz, 2.45 GHz and 2.36 GHz. Fig. 8. Measued 2.4GHz H-Plane adiation patten fo a 7- Element Dielectic Embedded SMTA at beam pointing diection, 90 (Blue); 60 (Red); 130 (Black); Simulated 90 (Cyan --) ; -3dB Beamwidth (Geen--). The decision paametes in the stuctual optimization fo this case study include the element heights, element aay adius as well as the dielectic adius and height. To educe optimization time, the element stuctual vaiables wee kept within limits that wee detemined by available mateial and the oveall size of the antenna. C. Results of Patch SMTA Figue 9 and Figue 10 illustate simulated and measued eflection coefficients and adiation patten of an optimized patch antenna aay with seven cicula elements (PASCE) and patch antenna aay with seven hexagonal elements (PASHE), espectively, when the paasitic element No. 6 is open-cicuited while the emaining shot-cicuited to gound.

5 Fig.9 Simulated and measued eflection coefficients of PASHE and PASCE, whee Measued S 11 of PASHE, Simulated S 11 of PASHE, Measued S 11 of PASCE and Simulated S 11 of PASCE. Radiation patten of PASHE in elevation plane Radiation patten of PASCE in elevation plane Fig.10. Simulated adiation patten of PASHE and PASCE in elevation plane when the main beam lobe is steeed in diffeent diections in azimuth plane. D. Result compaison of SMTAs Table 1 pesents the compaison of expeiment esults of SMTAs at the esonant fequency. The pototype SMTAs with fou diffeent stuctue configuations ae shown in Fig. 11. Table 1. Measued SMTA esults SMTA Reflection Fequency Gain (max.) coefficients Bandwidth (dbi) (S 11) db at -10dB Wie SMTA dbi 150 MHz DE SMTA dbi 320MHz Patch SMTA (PASHE ) dbi 140 MHz Patch SMTA (PASCE ) dbi 85 MHz Fig.11. Pototype SMTAs with fou diffeent stuctue configuations. V. Conclusion The pape pesented fou diffeent optimal designed low pofile SMTA aays. Wie SMTA and Patch SMTA can be used fo Access Point (AP), while DE-SMTA is suitable fo desktop o laptop compute in wieless netwok. The SMTA aays with switched beam-foming cicuit and algoithm can povide an ideal communication pefomance in the wieless communication and computing netwok, and futhe incease wieless secuity pefomances. Moeove, the pefomances of a low pofile SMTA aays can be impoved significantly if some compehensive multiobjective optimal methodology is implemented successfully, which is unde the way of investigating of the authos. Refeences [1] J. Sun, J. Lu and D. Ieland, Inceased Secuity Level using Space-division Appoval in Wieless Computing Netwok, Poceedings of APMC-2005, vol. 3, [2] R. Schlub, J. Lu and T. Ohia, Seven element gound skit monopole ESPAR antenna design fom a genetic algoithm and the finite element method, IEEE Tansactions on Antennas and Popagation, vol. 51, no. 11, pp , Nov [3] J. Lu, D. Ieland and R. Schlub: Dielectic Embedded ESPAR Antenna fo Wieless Communications Systems, IEEE Tans. on Antenna and Popagation, Vol. 52, No. 8, Aug. 2005, pp [4] M. Shi, J. Lu and D. Ieland, Smat Patch Antenna fo Indoo Mobile Wieless Computing, Poceedings of APMC-2005, vol. 3, pp , Dec