Compact Reflectometers for a Wideband Microwave Breast Cancer Detection System

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1 119 Africn Journl of Informtion nd Communiction Technology, Vol., No. 3, eptemer 006 Compct Reflectometers for Widend Microwve Brest Cncer Detection ystem Mrek E. Bilkowski, Fellow, IEEE, Norhudh emn, tudent Memer, IEEE, Amin Aosh nd Wee Chng Khor, tudent Memer, IEEE chool of Informtion Technology nd Electricl Engineering, The University of Queenslnd, t Luci, QLD, 4067 Austrli Astrct The design of compct widend microwve reflectometers for the purpose of inclusion in rest cncer detection system is presented. In this system, widend frequency source is used to synthesize nrrow pulse vi the step-frequency synthesis method. The reflectometer undertkes mesurements in the frequency domin nd the collected dt is trnsformed to the time/spce domin using IFFT. In order to ccomplish reflection coefficient mesurements over lrge frequency nd, compct widend couplers nd power dividers re used to form the reflectometer. Two compct six-port reflectometer configurtions re investigted. One uses the Lnge coupler nd the Gysel power divider nd the other one employs 3dB slot-coupled microstrip coupler nd -stge Wilkinson power divider. The reflectometer employing the slot-coupled coupler nd the Wilkinson divider provides wider opertionl ndwidth, s shown y simultion results performed with Agilent AD. Index Terms Cncer detection, microwve imging, experimentl verifiction, ner field. I. INTRODUCTION Brest cncer is the most common cncer dignosed in women in vrious prts of the world. In Austrli lone, it is estimted tht one in eleven Austrlin women will develop rest cncer t some stge in their life [1]. Erly detection nd effective tretment is the only wy to reduce the mortlity rte due to rest cncer. Currently the primry method for rest screening is X-ry mmmogrphy [], [3]. X-ry mmmogrphy hs sved mny lives, ut the technology still produces reltivity high numer of flse negtive nd flse positive dignoses. There is lso helth concern relted to exposure to ionizing rdition [3]. These fctors hve generted interest in lterntive pproches of rest cncer detection tht feture vrious degree of success. For exmple ultrsound is used cliniclly to discover whether lesion detected in mmmogrm is liquid cyst or solid tumour []. In ddition, Mgnetic Resonnce Imging hs een shown to e very useful screening tool, ut is very expensive nd not portle [4]. Recently, microwve imging hs een proposed s Mnuscript received April 11, 006. This work ws supported in prt y the Austrlin Reserch Council under Grnts DP nd DP vile lterntive to X-ry mmmogrphy. Microwve imging system is essentilly rest tissue rdr. It involves n ppliction of very low levels (1000 times less thn moile phone) of microwve energy through the rest tissue. The foundtion for tumour detection is difference etween the electricl properties of norml nd mlignnt rest tissue. Norml rest tissue is lrgely trnsprent to microwve rdition while lesions, which contin more wter nd lood, sctters microwves ck towrds the microwve source. The ntenn picks up these reflected signls nd they re nlysed using computer. A three dimensionl imge showing the loction of the cncerous tissue cn e otined s the outcome of this signl processing [3]. everl reserch groups, including the University of Wisconsin-Mdison nd Drtmouth Collge of the U, University of Clgry in Cnd, Technicl University Denmrk nd others re currently doing reserch in this new re [], [3], [5]. imilr ctivities hve lso een undertken t the University of Queenslnd in Austrli. The mjority of the developed microwve rest cncer detection prototypes re sed on the synthesized pulse technique, in which nrrow pulse is generted in the frequency domin [6]. This synthesized signl is lunched nd received y n ntenn which cn e moved in smll steps cross plnr or curved re in front of n imged oject. At ech loction of the proe ntenn, the received signl is processed with Vector Network Anlyser (VNA) which, y using its time domin cpility, provides suitle signl trnsformtion from frequency to time or spce domin. The mesurement system is controlled from PC. The collected dt is gthered nd processed y the PC to otin visul insight. The conventionl VNA with time-domin processing cpility is hndy to test nd proof the concept of the microwve rest cncer detection system. However, ecuse of its lrge size nd high cost it my e precluded in commercil rest cncer detection system. The purpose of the work presented in this pper is to replce the conventionl VNA y low-cost lterntive in the form of widend microwve six-port reflectometer. This pper is orgnised s follows, ection II, descries the experimentl setup required for microwve rest cncer detection system nd provides results otined using the conventionl VNA with time-domin processing cpility. ection III descries the design of widend /$00 - (C) 006 AJICT. All rights reserved.

2 10 Africn Journl of Informtion nd Communiction Technology, Vol., No. 3, eptemer 006 reflectometer. ection IV nd V compres two designs of the reflectometer, which use different types of couplers nd power dividers. ection VI concludes the pper. II. EXPERIMENTAL YTEM The configurtion of the prototype UWB rdr system is shown in Fig. 1. The system consists of -Y circulr cylindricl scnning pltform which includes turntle with resolution of.5 to support rest phntom, nd mechnicl scnning pltform in the Y direction hving resolution of 0.1mm. The scnning pltform supports proe ntenn which is in the form of n UWB tpered slot ntenn. This ntenn opertes in the frequency rnge from 3.1 GHz to 10.6 GHz [7]. A coxil cle is used to connect the proe ntenn to microwve Vector Network Anlyser (VNA), which is cple of mesuring the full set of - prmeters of port network. of reflection coefficients re completed, they re converted to the time/spce domin using IFFT. Hving otined the frequency nd time/spce domin dt for given loction, the results re stored in the PC nd the proe is moved to new position nd the mesurement procedure is repeted. The otined dt is then processed y the PC to crete n imge. Using flse colours, the loction of trget is identified in colour distinctive from those representing other prts of the rest phntom. The imging cpilities of the ove-descried UWB rdr system re crried out with respect to the experimentl setup s shown in Fig.. Fig.. Detils of n experimentl setup including n UWB tpered slot ntenn nd plstic continer with trget. Fig. 1. The configurtion of the microwve imging system. In the mesurement procedure descried in this pper, the VNA opertes only in the reflection coefficient mesurement mode. Prior to mesurements, the system is clirted over the frequency nd from 3.1 GHz to 10.6 GHz using modified one-port clirtion procedure. The coxil short nd shielded open circuit re used s in the stndrd clirtion procedure. However the coxil mtch termintion is replced y lod relized y the proe ntenn rditing microwve signl in free spce [8]. We cll this modified clirtion procedure s Method A. By using Method A, undesired signls including internl reflections inside the proe ntenn nd t the ntenn-ir interfce re either reduced or removed completely [8]. The mesurement process is s follows. First, n re to e scnned is specified. The required informtion concerns the step size nd numer of steps in the -Y scnning pltform. At ech -Y proe loction, the PC controller triggers the source in the Vector Network Anlyser nd 50 to 800 (depending on specifictions) mesurement points for reflection coefficient over the frequency nd of interest re performed. After the frequency domin mesurements The rest phntom is formed y circulr cylindricl plstic continer with dimeter of 1.5cm with thickness of 1mm. The continer is filled with vegetle oil with reltive dielectric constnt of 4. The continer nd oil re used to represent the skin lyer nd rest tissue. A smll plstic continer filled with wter (with reltive dielectric constnt of 80) representing the tumour is locted close to the centre of the first plstic continer. This phntom provides quite good pproximtion to the ctul helthy rest tissues nd cncerous tumours, which hve typicl reltive dielectric constnts of 9 nd 50, respectively [9]. Y Loction (cm) Plstic Continer Wter Trget X Loction (cm) Fig. 3. The time domin reflection mesurement result for plstic continer filled with ir, using the modified clirtion technique /$00 - (C) 006 AJICT. All rights reserved.

3 11 Africn Journl of Informtion nd Communiction Technology, Vol., No. 3, eptemer 006 Fig.3 shows the imging result when the system is clirted using Method A. In these figure the oundries of the plstic continer nd the loction, size nd shpe of the wter trget re clerly oserved. The mesured dimeter of the wter trget is pproximtely 3.3cm nd is quite close to the ctul one of 3cm III. IX PORT DEIGN Our next gol is to replce the VNA (of Fig. 1) y six-port reflectometer composed of widend couplers, dividers nd sclr detectors. The configurtion of the sixport which is investigted here is shown in Fig Γ = / = Γ + jγ (1) Q 1 D () 1 j j 1 Fig. 5. The sic rules for the opertion of Qudrture hyrid () In-phse two-wy power divider. By considering the sic rule for opertion of Q hyrid nd D hyrid, s shown in the Fig. 5, the output signls t Port 3 to Port 7 of the reflectometer of Fig.4 re given s shown in equtions ()-(6). Fig. 4. Configurtion of six-port reflectometer with the reltime disply cpility. This configurtion, introduced in [10], offers rel-time disply of the mesured complex reflection coefficient [11-13]. It includes qudrture hyrids (Q), nd two-wy power dividers (D). Also shown in Fig. 4 re sclr power detectors connected to ports 3-7, microwve source connected to port 1 nd Device Under Test (DUT) connected to port. The prt of the reflectometer enclosed y roken line is clled Complex Rtio Mesuring Unit (CRMU) or correltor. The Q hyrid outside the CRMU is employed to redirect reflected signl, nd n incident signl, t DUT to perform reflection-type mesurements. Other circuits outside the CRMU cn e used to redirect signls, to perform trnsmission-type mesurements. The divider D, outside the CRMU, terminted y sclr detector t P3 is used to monitor the signl source power level. This signl cn e treted s reference signl. It cn e used in feedck loop to mintin constnt power level from the source. Eqution (1) defines the complex reflection coefficient s the rtio of the reflected signl from DUT, nd the incident signl t DUT,. 3 = j () 4 = ( Γ1 + j( Γ + 1) ) (3) 5 = j ( Γ1 + j( Γ 1) ) (4) 6 = (( Γ1 + 1) + jγ ) (5) 7 = j (( Γ1 1) + jγ ) (6) Assuming tht the power detectors re identicl nd operte in the squre-lw region, the power vlues P 3, P 4, P 5, P 6, P 7 s mesured y the detectors re given y (7): i i P = where i=3,4,5,6 nd 7 (7) Using (7) in conjunction with (-6), it cn e proved tht the complex reflection coefficient (1) is relted to the mesured powers t Port 3 to 7 (P 3, P 4, P 5, P 6, P 7 ) y the following expression (8): P P P P Γ = = Γ1 + jγ = + j (8) P3 P3 This expression indictes tht for the reflectometer configurtion of Fig. 4, the complex reflection coefficient,, cn e otined y mesuring voltges t the output of the squre-lw detectors. In the system controlled vi PC, /$00 - (C) 006 AJICT. All rights reserved.

4 1 Africn Journl of Informtion nd Communiction Technology, Vol., No. 3, eptemer 006 this tsk cn e ccomplished using precision ADC crd connected to the detectors. The PC monitor cn e used to disply in the polr or other formts. IV. TWO REFLECTOMETER CONFIGURATION The six-port reflectometer of Fig. 4 cn e relized in microstrip or stripline technology. Its performnce will depend on the opertion of the chosen Q nd D hyrids. Two types of couplers nd two types of power dividers in microstrip technology to construct Q nd D hyrids re chosen to design two widend reflectometers. In the first design, the 3dB Lnge coupler [14] nd the Gysel power splitter [15] re selected s the Q nd D hyrids. In the lterntive design, 3dB slot-coupled microstrip coupler nd -wy Wilkinson power divider re chosen s the reflectometer s components. Although the lterntive im is to hve the two designs for the GHz nd, we hve found tht the first configurtion hs difficulty to meet this gol. Becuse of these resons, the presented results for the first reflectometer re limited to the 4-8 GHz nd. A. Lnge Coupler nd Gysel Power plitter The configurtions of the Lnge coupler (consisting of 8 prllel strips with vrying width, spcing nd length) nd the Gysel power splitter to form widend 6-port reflectometer (of Fig. 4) re presented in Fig. 6. The performnce of individul components is optimized y strting the design t the centre frequency of 6 GHz. The initil prmeters re worked out using the design guidelines ville from [14], [15]. It is worthwhile to mention tht the selected Lnge coupler needs wire crossover etween very nrrow strips (usully in the order of micro millimetre). In turn, the Gysel power divider is incple of providing the required ( GHz) multi-octve ndwidth performnce. In order to otin the reflectometer with improved opertionl ndwidth new components re considered to form the second 6-port reflectometer. B. 3dB lot-coupled Microstrip Coupler nd Wilkinson Power Divider In the lterntive design, -stge Wilkinson power divider, s shown in Fig. 7 [16] nd slot-coupled microstrip coupler, s shown in Fig. 7(), re selected to form the reflectometer of Fig. 4. Port 1 Port Port 3 Port 4 Fig. 6. () Configurtions of Lnge nd () Gysel hyrids. Fig. 7. Configurtions of Wilkinson power divider nd () 3dB slot-coupled microstrip coupler. An explntion is required for the microstrip slotcoupled coupler. It is new component, which hs een recently proposed in [17]. The coupler hs 3 conductor lyers with sustrtes etween ech lyer. Upper nd lower lyer consist of identicl ellipticl shped conductor ptches with microstrip Ports 1- nd 3-4, respectively. These two ptches re coupled y n ellipticl slot, which is in the middle conducting lyer forming common ground plne. The very importnt ttriute of this coupler is its ility to offer very widend performnce while preserving its very compct size. () /$00 - (C) 006 AJICT. All rights reserved.

5 13 Africn Journl of Informtion nd Communiction Technology, Vol., No. 3, eptemer 006 V. PERFORMANCE COMPARION Using two sets of Q nd D hyrids, two 6-port designs re ccomplished. Their performnce is ssessed using Agilent AD [18]. A. First Reflectometer The first 6-port reflectometer uses the Lnge coupler nd the Gysel power splitter. Fig. 8 nd 9 show the simultion results for specific DUTs such s short, open nd mtch. Assuming the use of idel squre-lw detectors, the reflection coefficient,, ws clculted using expression (9) tht is nlogous to (8): = = Γ1 + jγ = j Γ (9) Fig. 8. Reflection coefficient determined y the first reflectometer for DUT in the form of mtched lod. As oserved in Fig. 8, the six-port reflectometer gives reflection coefficient, of 0.1±0.07 cross the 4 GHz ndwidth when mtched lod represent DUT. The oserved devition from the idel cse of zero is due to the non-idel performnces of individul components forming the reflectometer. Fig. 9-() show the simultion results when DUT represents either short or open circuit. The reflection coefficient, hs mgnitude of 1±0.5. The overll results in Fig. 8 nd 9 indicte resonle performnce of the six-port reflectometer over one octve (4-8 GHz) frequency nd. B. econd Reflectometer The next simultions concern the performnce of the second six-port reflectometer, which is formed y the 3 db slot-coupled microstrip coupler nd the Wilkinson power divider representing the Q nd D hyrids in Fig. 4. As in the cse of the first reflectometer, we ssume the idel squre lw opertion of the detectors. The simultion results re shown in Fig. 10 nd 11. Fig. 10 presents the reflection coefficient,, of the sixport reflectometer when the DUT is mtched lod. Mgnitude of 0.1±0.1 is otined from 3GHz to 10.6GHZ. () Fig. 9. Reflection coefficient determined y the first reflectometer for DUT in the form of open, nd () short circuit. Fig. 10. Reflection coefficient determined y the second reflectometer for DUT in the form of mtched lod. In turn, in Fig. 11 the reflection coefficient,, with mgnitude of 0.88±0.13 is oserved when DUT is in the form of either short or open circuit. The oserved devitions re due to the non-idel response of the components forming the reflectometer. When compring the two reflectometer configurtions, one finds tht the use of the 3 db slot-coupled microstrip coupler nd the - stge Wilkinson power divider results in the wider opertionl ndwidth, which is now 7.6 GHz. The non-idel opertion of the two configurtions of the reflectometer cn e corrected y suitle clirtion procedure. For the investigted 6-port configurtions, this tsk cn e ccomplished using the procedure involving 5 or 6 clirtion stndrds, s descried in [10-13]. Note tht s the results for the DUT reflection coefficient otined in the frequency domin need to e trnsformed to the time domin, the oserved in Fig /$00 - (C) 006 AJICT. All rights reserved.

6 14 Africn Journl of Informtion nd Communiction Technology, Vol., No. 3, eptemer 006 devitions from ctul vlues my e found tolerle. reflectometer is cple to operte over n ultr wide frequency nd, which is from 3.1 to 10.6GHz. ACKNOWLEDGEMENT The uthors cknowledge the finncil support of the Austrlin Reserch Council vi Grnts DP nd DP () Fig. 11. Reflection coefficient determined y the second reflectometer for DUT in the form of open or () short circuit. As result, one my find no need for strict clirtion of the presented reflectometers. imple clirtion procedures to remove smll devitions etween the ctul nd simulted vlues of the DUT reflection coefficient re currently investigted y our reserch tem. VI. CONCLUION The design of two widend microwve reflectometers for the purpose of inclusion in microwve rest cncer detection system hs een presented. In this system, widend frequency source is used to synthesize nrrow pulse vi the step-frequency synthesis method to illuminte n imged ody. The reflectometer undertkes mesurements in the frequency domin nd the collected dt is trnsformed into the time/spce domin using n IFFT. A specil configurtion of six-port reflectometer, which enles the mesurement nd disply of the complex reflection coefficient in rel-time y pplying simple mthemticl trnsformtions of the mesured voltges t the outputs of sclr (power) detectors hs een descried. One of the designed reflectometers uses the Lnge coupler nd the Gysel power splitter s its uilding locks. The other one employs slot-coupled microstrip coupler nd -stge Wilkinson divider, s its constituting components. The opertion of the two reflectometers hs een investigted with the use of Agilent AD. It hs een shown tht the second REFERENCE [1] Austrlin Institute of Helth nd Welfre & Austrlsin Assocition of Cncer Registries (AACR), Cncer in Austrli 001, AIHW ct. No.CAN3. Cnerr: AIHW (Cncer eries no. 8), pp , 004. [] E.C. Fer,.C. Hgness, P.M. Meney, M. Okoniewski nd M.A. tuchly, Enhncing rest tumor detection with ner-field imging, IEEE Micro, pp , Mrch 00. [3] E.C. Fer P.M. Meney nd M.A. tuchly, Microwve for rest cncer detection, IEEE Potentils, pp. 1-18, 003. [4] MARIB study group, creening with mgnetic resonnce imging nd mmmogrphy of UK popultion t high fmilil risk of rest cncer: A prospective multicentre cohort study, The Lncet, vol. 365, pp , 005. [5] Title: Microwve imging for rest-cncer screening Aville t: ng.html [6] D.A. Noon nd M.E. Bilkowski., "An inexpensive microwve distnce mesuring system," Microwve nd Opticl Technology Letters, vol. 6, no. 5, pp. 87-9, April [7] A. Aosh, H.K. Kn nd M.E. Bilkowski A Compct UWB plnr tpered slot ntenn For use in microwve imging system Microwve nd Opticl Techn. Letters, vol. 48, no.11, pp. 1-16, Nov [8] W.C. Khor nd M.E. Bilkowski, Investigtions into cylindricl nd plnr configurtions of microwve imging system for rest cncer detection Proc. IEEE Antenns nd Propgtion ociety Interntionl ymposium, pp , Aluquerque, New Mexico, UA, Jul 006. [9] E. J. Bond, X. Li,. C. Hgness, nd B. D. Vn Veen, Microwve imging vi spce-time emforming for erly detection of rest cncer, IEEE Trns. Antenns Propg., vol. 51, no. 8, pp [10] C.A. Hoer, A microwve network nlyzer using two 6-port reflectometers, Microwve ymposium Digest, MTT- Interntionl, vol. 77, issue 1, pp , June [11]. tuchly, M.E. Bilkowski, K. Cput, nd W. Guo, Microwve level guging system, Proc.10th Int. Microwve Conference, MIKON 94, Ksiz, Polnd, pp , My 30-June, [1] M.E. Bilkowski nd A.P. Dimitrios, "A step-frequency six-port network nlyser with rel-time disply", AEU Intl. Journl of Electronics nd Communictions, vol. 47, no. 3, pp , [13] G.F. Engen, An improved circuit for implementing the six-port technique of microwve mesurements, IEEE Trns. Microwve Theory Tech., vol. MTT-5, no.1, pp , Dec [14] J. Lnge, Interdigitted stripline qudrture hyrid, IEEE Trns. Microwve Theory Techn., pp , Dec [15] U. Gysel, A new N-wy power divider/cominer suitle for high-power pplictions, Microwve ymposium Digest, MTT- Interntionl, vol. 75, no. 1, pp , [16] M. L. Edwrds, Microwve & RF circuits: nlysis, design, friction, & mesurement, ept [17] M.E. Bilkowski nd A. M. Aosh, Design of compct UWB 3dB coupler sumitted for puliction, 006. [18] Agilent Technologies Advnced Design ystem 00 - Pssive Circuit Design Guide, Fe /$00 - (C) 006 AJICT. All rights reserved.

7 15 Africn Journl of Informtion nd Communiction Technology, Vol., No. 3, eptemer 006 Mrek E. Bilkowski (M 88 F 03) ws orn in ochczew, Polnd. He received the M.Eng.c. degree (1974) in pplied mthemtics nd the Ph.D degree (1979) in electricl engineering oth from the Wrsw University of Technology nd higher doctorte (D.c. Eng.) in computer science nd electricl engineering from the University of Queenslnd (000). He held teching nd reserch ppointments t universities in Polnd, Irelnd, Austrli, UK, Cnd, ingpore, Hong Kong nd witzerlnd. At present he is Professor in the chool of Informtion Technology nd Electricl Engineering t the University of Queenslnd. His reserch interests include ntenns for moile cellulr nd stellite communictions, signl processing techniques for smrt ntenns, low profile ntenns for reception of stellite rodcst TV progrms, nerfield/fr-field ntenn mesurements, electromgnetic modelling of wveguide feeds nd trnsitions, conventionl nd sptil power comining techniques, six-port vector network nlysers, nd medicl nd industril pplictions of microwves. He hs pulished over 450 technicl ppers, severl ook chpters nd one ook. Prof. Bilkowski ws Co-recipient of 000 Hrold A. Wheeler Applictions Prize Honourle Mention for pper pulished in the IEEE TRANACTION ON ANTENNA AND PROPAGATION in In 00, he ws elected n IEEE Fellow for contriutions to the modelling, design, nd testing of microwve guiding nd rditing structures. Norhudh emn ( 06) ws orn in Johore, Mlysi. he received BEng degree (003) in Electricl Engineering (Telecommuniction) from the University Technology of Mlysi, Mlysi nd M.Eng degree (005) in Rdio Frequency / Microwve Communictions from The University of Queenslnd, Austrli. In 003, she ws employed s n engineer in Motorol Technology, Penng, Mlysi where she worked on RF nd microwve components design nd testing. Currently, she is PhD student t The University of Queenslnd. Her reserch interests concern the design of microwve circuits for iomedicl nd industril pplictions, ultr widend technologies nd moile communictions. Amin M. Aosh ws orn in Mosul, Irq. He received the Mc in communictions systems nd PhD in microwve engineering in 1991 nd 1996 respectively oth from Mosul University. He worked s Hed of Computer & Informtion Engineering Deprtment, Mosul University, until 003. In 004, he joined the Griffith University nd then the University of Queenslnd, Austrli, s Reserch Fellow. His reserch interests include ntenns, rdio wve propgtion nd microwve devices. Wee Chng Khor ( 05) ws orn in ingpore. He received the B.Eng. degree in Electricl Engineering with Honours Clss I from the University of Queenslnd in 003. ince 004, he hs een Ph.D. student nd Reserch Assistnt in the chool of Informtion Technology nd Electricl Engineering t the University of Queenslnd. His reserch interests include medicl nd industril pplictions of microwves /$00 - (C) 006 AJICT. All rights reserved.