Space Leaky Waves Propagating along a Pair of CRLH SIW Lines

Transcription

1 RADIOENGINEERING, VOL. 27, NO. 3, SEPTEMBER Space Leaky Waves Popagating along a Pai of CRLH SIW Lines Rihem NOUMI 1, Jan MACHAC 2, Ali GHARSALLAH 1 1 Dept. of Physics, Faculty of Sciences of Tunis, Univesity of Tunis El Mana, 2092, Tunis, Tunisia 2 Dept. of Electomagnetic Field, Faculty of Electical Engineeing, Czech Technical Univesity in Pague, Technicka 2, Pague 6, Czech Republic noumii.ihem@gmail.com Submitted Januay 4, 2018 / Accepted July 17, 2018 Abstact. A space leaky wave excited on composite ightleft handed substate integated waveguide and adiating in a wide fequency band is pesented in this pape. The poposed two line aay is a good candidate fo smat systems of monitoing and tacking applications. The system is composed of two diffeent lines that ae placed in paallel on the same substate. Simulation esults show that the fist line leaks enegy in the band fom 6.9 to 11 GHz with a 7.8 GHz boadside adiation fequency and the second line leaks in the band fom 8.9 to 13.8 GHz; the elated boadside adiation fequency is 10.2 GHz. Complex single/dual scanned beams ae obtained in a wide ange of angles fom 72 to +73. The simulations wee caied out in the CST Micowave Studio and the obtained measuement esults match well with the theoetical analysis descibed in this pape. Keywods Space leaky wave, substate integated waveguide, composite ight-left handed line 1. Intoduction Since the advent of substate integated waveguide (SIW) in the micowave engineeing society, many eseaches have apidly valued the impotance of this technology thanks to its minimal loss, ease of fabication, low cost and small size compaed to the ectangula waveguide [1 4]. In ecent yeas, leakage of enegy fom SIW has been widely studied fo its outstanding advantages elated to the continuous beam steeing of the leaky field distibution. Seveal woks wee focused on the design of dual-beam leaky wave antennas [5 8]. They ae pefeed fo both thei low pofiles and loss and also mainly fo thei scanning flexibility especially fo the systems that equie multiple coveage of spaces. This wok investigates the popagation of space leaky wave along SIW CRLH tansmission line. In the case of a single line, the behavio of the space leaky wave is well known, see e.g. [9], [10]. A complex phenomenon has been evealed in the case of a pai of the CRLH SIW tansmission lines designed on a common substate. These two lines ae tuned to diffeent fequencies. In this case, the two tansmission lines ae fed into opposite teminals. The emaining teminals ae matched. The field adiated by the pai of space leaky waves depends stongly on the phase shift between feeding signals. When the phase shift is equal to 180, the adiated field offes two main beams at most fequencies. The boadside adiation which is pependicula to the lines diection appeas at the oiginal fequencies of the paticula waves. The poposed pai of tansmission lines can scan both single and double beams depending on the fequency ange, coesponding to a beam of the fist antenna (o the second one) and two simultaneous beams fom both lines, espectively. This beam steeing is obtained fom 72 to 73 with eaching boadside adiation at 7.8 and 10.2 GHz. Futhemoe, the cuent design featues an asymmetic dual beam scanning and opeates in a wide fequency bandwidth fom 6.9 GHz to 13.5 GHz. The wok pesented in this pape illustates a complex behavio of leakage fom open tansmission lines. This design can be an attactive featue fo smat potecting systems that ae used in a complex space geomety and fo scanning systems and tacking applications. 2. Theoy: Leakage fom SIW Lines The leaky wave popagates along a tansmission line as the mode with a complex popagation constant k z [10]: kz j. (1) Thee ae two kinds of leaky waves, distinguished by the elation of thei phase constant to the popagation constant in a suounding medium. The substate leaky wave mode fulfills the phase condition fo < k TM (o k TE ) whee k TM o k TE ae phase constants of the coesponding suface wave popagating in a substate. Space leaky wave DOI: /e ELECTROMAGNETICS

2 634 R. NOUMI, J. MACHAC, A. GHARSALLAH, SPACE LEAKY WAVES PROPAGATING ALONG A PAIR OF CRLH SIW LINES (popagating along open tansmission line) fulfills the phase condition < k 0 whee k 0 is the fee space popagation constant. Space leaky wave adiates powe fom the tansmission line into the space above it. Now contols the adiated beam angle, and is the leakage ate which contols the beam width [11]. Theoetically, the space leaky wave field inceases to infinity in a pependicula diection to the line substate. The eal adiated field must fulfill the adiation condition in infinity. Theefoe, afte eaching its maximum at the appoximate diection detemined by the θ angle, the field deceases again to meet the adiation condition cos max. (2) k The phase constant is positive in the case of a standad tansmission line. In this instance, the field is adiated only in a fowad diection as e.g. in [12]. The composite ightleft handed (CRLH) line substantially impoves the adiation and theefoe the line applicability. The phase constant can be negative as well as positive. Hence, the space leaky wave adiates depending on fequency both in the backwad and fowad diections. The cuent of this wave can be appoximated by a simple function I z I exp jk z I exp z exp j z. (3) 0 z 0 The wave popagates along the line and leaks powe to the space and theefoe its amplitude deceases along the line. Due to the leakage caused by such a wave, the adiation patten can simply be calculated by [11] L j 0 ' ' 1 1 exp j 0 sin exp j z1cos d. 4 0 E I k k z z I 1 is the cuent amplitude at the feeding point at z = 0. Depending on the phase constant sign, a leakage in backwad o fowad diections was obtained. The poposed stuctue is composed of an aay of two CRLH SIW lines positioned along the z-axis as shown in Fig. 1. The two lines have diffeent fequencies of the boadside adiation at which the phase constant is zeo. The lengths of thei unit cells must be equal as the lines must have the same length. Fo analysis puposes, coupling between the two lines is consideed to be negligible. The total adiated field of the two SIW lines is given by 0 (4) E E E exp j, total 1 2 (5) with E 1 detemined by (4), and similaly with E 2 L j0 2 0 z2 4 0 I exp jk exp j sin exp jk cos z dz " " (6) whee thephase shift between the two feeding pots is equal to 180, L is the length of the leaky wave CRLH line stuctue, E 1 is the adiated field of the fist CRLH SIW Fig. 1. Layout of the aay of the two CRLH SIW lines. The dimensions ae: L = 205 mm and W = 29.3 mm: the input pots with opposite phase of φ = 180 ae pot 1 and pot 2. Pot 3 and pot 4 ae matched by 50 Ω loads. Diection chaacteistics (backwad, boadside, fowad) ae shown. line, E 2 is the adiated field of the second CRLH SIW line and k z1 and k z2 ae the complex popagation constants of the fist and the second lines, espectively. The integation of (4) and (6) gives the following adiated field fomulas j0 E 1 I1 expjk0sin 4 (7) exp j Lk ( 0cos )expj L( 1 j 1) 1, j( k0cos ( 1 j 1)) j0 E 2 I2 expjk0sin 4 (8) exp j Lk ( 0cos )expj L( 2 j 2) 1. j( k0cos ( 2 j 2)) 3. Poposed Stuctue of Tansmission Lines The poposed pototype of the two paallel CRLH SIW tansmission lines that ae shown in Fig. 1 has been designed to veify the scanning pocess of the two space leaky wave supeposition. The lines adiate though peiodic inte-digital capacito slots etched on the uppe face of the SIW. Roges substate 5880 with a elative pemittivity of 2.2 and a thickness of mm is used. The lines ae fed via two input pots at opposite ends which ae excited simultaneously with a phase shift, among them = 180. As the fist step of the design, two diffeent SIW CRLH cells opeating in diffeent fequency bands ae consideed. The two lines ae designed to be in the balance case, i.e. without a stop band. The fequencies of boadside adiation ( = 0) ae located at 7.8 GHz and 10.2 GHz fo the fist and second cells, espectively. The coesponding cell layouts ae shown in Fig. 2. The side walls of these models ae made-up by solid PEC walls to simplify the simulation pocess. An inte-digital slot etched on the uppe face of the SIW cells seves as a seies capacito. In addition, two inductance pins ae inseted into the left side of each unit cell. The distance between these two pins is an impotant facto allowing the eduction of the stop band, and a balanced state is obtained by optimizing the value of

3 RADIOENGINEERING, VOL. 27, NO. 3, SEPTEMBER As mentioned peviously, the unit cells ae constucted using PEC side walls. In ode to include the SIW vias in the design, the physical paametes of the SIW ae valued as follows: the effective width w siw is calculated fom a good estimation of the w ec / w siw elation defined in [14]. The values of the d diamete of the vias and the s distance between two consecutive vias ae calculated fom (9) and (10) [15], [16]: d /5, (9) g (a) (b) Fig. 2. Unit cell of the poposed CRLH SIW lines: (a) Unit cell of the fist CRLH line. (b) Unit cell of the second CRLH line. Dimensions ae given in Tab. 1. Paametes p l 1 l 2 w 1 w 2 w eff2 Value (mm) Paametes w eff1 l 3 l 4 w 3 w 4 Value (mm) Tab. 1. Dimensions of the poposed unit cell. Fig. 3. Dispesion diagams fo the fist and the second CRLH SIW unit cells shown in Fig. 2. this distance. This type of the SIW CRLH TL single cell and its theoetical backgound have aleady been epoted in [9], [10]. The dimensions of the two diffeent tansmission lines ae listed in Tab. 1. The beam scanning ange and coesponding fequency bands can be estimated fom dispesion elations of the two CRLH SIW unit cells as well as fom the k 0 ailine which defines the leakage egion ( < k 0 ). Obseved esults show that the two cells ae balanced. The LH egion of the fist line is given by the band GHz and the RH egion band is among GHz. Fo the second line, the LH egion band is given fom 8.9 to 10.2 GHz wheeas the RH egion band is set fom 10.2 to 13.8 GHz. The new phenomena pesented by this design show that the space leaky waves can popagate simultaneously along the two lines fom 8.9 until 10.2 GHz with 1 > 0 and 2 < 0 and fom 10.2 to 11 GHz with 1 > 0 and 2 > 0. Howeve, fo the fist line, a naow stop band appeas aound 11.8 GHz. This can be explained by the appeaance of a paasitic esonance attained fom the inte-digital finges [13]. s 2d (10) whee g is the guided wavelength along the SIW. In the final optimum design, the two paallel SIW lines ae located on a common substate, each consisting of 25 unit cells of the same length. Tapeed micostip-to- SIW tansitions ae used to powe the consideed stuctue. In addition, the distance between the two lines was optimized to veify the coupling between the feeding pots. Results show that only one ow of SIW pins is sufficient to neglect the coupling, as illustated in Fig. 1. The final paametes of the pai CRLH SIW lines ae listed in Tab. 2. The influence of the phase diffeence between feeding pot signals to the field distibution is documented in Fig. 4. Hee, the field distibution calculated by (7) and (8) shows that a single beam at 9.2 GHz can be acquied only when = 180. The aim is to get one beam that is naowe than the two beams at othe fequencies. This single beam adiates moe effectively. It is shown by the plot in Fig. 4 calculated at the fequency 9.2 GHz. The field distibution of space leaky waves was calculated by (5), (7), and (8). The values of k z1 and k z2 ae taken fom the dispesion elations of the fist and second SIW CRLH unit cells plotted in Fig. 3. Figue 5 summaizes the analytical development of the steeing behavio ove the fequency of the main beam diections poduced by leaky waves with the phase diffeence equal to 180. The measued esults ae also plotted in Fig. 5. The steeing ange is given fom 72 to +73 in the fequency band Paametes L d s w siw1 w siw2 Value (mm) Tab. 2. Dimensions of the poposed stuctue. Fig. 4. Analytical esults of a nomalized E-field distibution calculated by (7) and (8) in dependence on phase diffeence at 9.2 GHz.

4 636 R. NOUMI, J. MACHAC, A. GHARSALLAH, SPACE LEAKY WAVES PROPAGATING ALONG A PAIR OF CRLH SIW LINES Fig. 5. Measued and theoetical analysis esults of main beam diections of the two leaky waves excited on the two paallel CRLH SIW lines. fom 7 to 13.5 GHz. Moe pecisely, the obseved esults demonstate that fom 7 GHz to 8.7 GHz only the wave that is tavelling along the fist line adiates. In the band GHz, the pai of tansmission lines adiates togethe two asymmetical beams, and finally, fom 11 until 13.5 GHz, only the wave tavelling along the second tansmission line adiates. 4. Simulated and Expeimental Results and Discussion The pototype of the CRLH SIW two line aay designed in Sec. 2 has been fabicated. Figue 6 shows the photogaph of the fabicated stuctue. The lines ae fed via two input SMA pots at opposite ends excited simultaneously with phase shift between them = 180. The isolation between pots S 21 and S 41 is pesented in Fig. 7. It can be obseved that the coupling between the pots is significant since the isolation is kept bellow 20 db. Scatteing paametes wee measued by the Rohde & Schwaz ZV 67 vecto netwok analyze. Figue 8 shows the simulated and measued esults. As peviously mentioned, the system was designed caefully to get unit cells balanced. Simulation esults show a continuous opeation of the antenna system in the fequency band GHz. Howeve, measued esults show that the pai of the antennas has not been fabicated popely and at Fig. 7. Simulated isolation esults between pot 2 and pot 1 and between pot 4 and pot 3 of the poposed pai of SIW CRLH tansmission lines. both aeas of boadside adiation, they show stop bands [17] that have not been evealed via simulation. The appeaance of the stop band is vey sensitive to the dimensions of the fabicated stuctues. Additionally, the matching of measued S 11 ae slightly high, especially in the left hand egions. This can be attibuted to the mismatch of SMA connectos that ae not consideed in the simulation. The supeposition of the two space leaky waves was measued in an anechoic chambe at diffeent fequencies. The two lines wee simultaneously fed by the ZVA67 analyze with a 180 phase shift. The ZVA40 analyze eceived tansmitted signal fom the system. Moeove, a DHR20 antenna was used fo the test [18]. Figue 9 compaes the simulated and measued nomalized powe pattens at some paticula fequencies: when the fist line is only adiating, when both lines ae adiating and when the second line is only adiating, at f = 7.8 GHz, f = 9.4 GHz and f = 12.5 GHz, espectively. A good ageement between both the measued and simulated data is obtained. This veifies the poposed complex vaiation of the two space leaky wave field. The measued diections of adiation maxima at paticula fequencies wee compaed with the theoetical analysis in Fig. 5 (7) and (8). The fit with angles obtained fom the simplified analysis is vey good. Moe details of the adiation behavio ae illustated in Tab. 3. Figue 10 shows simulated adiation pattens in the H- plane. The angle is hee set at the diection of the maximum adiation at each fequency. Plots show only one main lobe in this plane that is equied. Fig. 6. Photogaph of the fabicated system composed of a pai of CRLH SIW lines. Fig. 8. Simulated and measued S 11 of the poposed stuctue.

5 RADIOENGINEERING, VOL. 27, NO. 3, SEPTEMBER (a) Fig. 10. Simulated H-plane adiation pattens at f = 7.2 GHz, f = 10.5 GHz and f = 13 GHz. (b) Fig. 11. Measued gain and adiation efficiency of the poposed system. (c) Fig. 9. Nomalized powe pattens, measuement vs. simulation at (a) f = 7.8 GHz (when the fist line is only adiating); (b) f = 9.4 GHz (when both lines ae adiating); (c) f = 12.5 GHz (when the second line is only adiating); (blue line: measuement; ed line: simulation). Fig. 12. Measued and simulated Side Lobe Level of the poposed system. Fequency band (GHz) β 1 of the fist CRLH line β 2 of thefist CRLH line Main beam numbes β 1 < 0 Not adiating One beam 7.8 β 1 =0 (θ = 0) Not adiating One beam β 1 > 0 Not adiating One beam β 1 > 0 β 2 < 0 Two beams 9.3 β 1 = β 2 One beam β 1 > 0 β 2 < 0 Two beams 10.2 β 1 > 0 β 2 = 0 (θ = 0) Two beams β 1 > 0 β 2 > 0 Two beams Not adiating β 2 > 0 One beam Tab. 3. Steeing behavio of the pai of SIW CRLH LWA.

6 638 R. NOUMI, J. MACHAC, A. GHARSALLAH, SPACE LEAKY WAVES PROPAGATING ALONG A PAIR OF CRLH SIW LINES Antenna type Impedance fequency band (GHz) Maximum Gain (db) Boadside adiation (θ= 0) [6] Micostip LWA no [7] Active LWA Not epoted no [8] Tiple peiodic micostip LWA This wok CRLH SIW LWA system 3-8: with two stong stop band at 4 and (with two stop bands aound 7.8 and 10.2) 0.8 no 15.2 yes Scanning type Symmetical dual beams at φ diection Asymmetical dual beams Symmetical and asymmetical dual beams Single beam and asymmetical dual beams Beam scanning ange (75 ; 48 ) to (38 ;60 ) (24 ; 46 ) (128 ; 150 ) (36 ; 72 ) ( 34 ; 46 ) ( 50 ; 72 ) ( 73 ; 62 ) Tab. 4. Compaison between poposed and in the liteatue epoted dual beam antennas. The measued gain and adiation efficiency of the system ae plotted in Fig. 11. The obseved esults show that a high gain value is obtained in the entie impedance bandwidth and a maximum of 15.8 db is detected at 11.4 GHz. In addition, high adiation efficiency is calculated with an aveage value of 90%. Those esults pove the eliability of the poposed system. Simulated and measued esults of side lobe level (SLL) in some paticula fequencies ove the adiating fequency band ae shown in Fig. 12. It can be noticed that low SLL is obtained in the aeas whee only one main beam is steeed and it inceases with the appeaance of the second adiating beam. Moeove, simulated esults coespond well to the measued ones. Table 4 povides the pefomance compaison between the poposed wok and othe designs taken fom liteatue. It is vey obvious that the wok pesented in this pape has a wide band of opeation and scanning ange as well as a highe maximum gain value than most pevious studies. 5. Conclusion In this pape, the supeposition of space leaky waves that ae excited on the CRLH SIW line system is oiginally pesented. The poposed stuctue exhibits a complex beam steeing behavio ove a wide fequency band. A bief theoetical analysis is conducted to pove the idea of the design. The theoetical and measuement esults wee compaed and a good ageement has been evealed. An asymmetical dual beam steeing behavio of leakage field distibution ove the fequency band fom 6.9 to 13.5 GHz has been obtained with a wide band of scanning ange fom 72 to +73. The poposed stuctue is suitable fo smat systems which can be used to monito a space with a complex geomety and fo beam tacking systems as well. Acknowledgments This wok was suppoted by the Gant Agency of the Czech Republic unde Poject S. Refeences [1] LIU, J., JACKSON, D., LONG, Y. Substate integated waveguide (SIW) leaky-wave antenna with tansvese slots. IEEE Tansactions on Antennas and Popagation, 2012, vol. 60, no. 1, p DOI: /TAP [2] CASSIVI, Y. PERREGRINI, L., ARCIONI, P., et al. Dispesion chaacteistics of substate integated ectangula waveguide. IEEE Micowave and Wieless Components Lettes, 2002, vol. 12, no. 9, p DOI: /LMWC [3] XU, F., WU, K. Numeical multimode calibation technique fo extaction of complex popagation constants of substate integated waveguide. In IEEE MTT-S Intenational Micowave Symposium Digest, 2004, vol. 2, p DOI: /MWSYM [4] RABAANI, K., BOULEJFEN, N. Chaacteistic impedance and popagation constant assessment of substate integated waveguide tansmission line. In th Intenational Design & Test Symposium (IDT). Hammamet (Tunisia), DOI: /IDT [5] LI, Y., XUE, Q., YUNG, E. K.-N., et al. Dual-beam steeing micostip leaky wave antenna with fixed opeating fequency. IEEE Tansactions on Antennas and Popagation, 2008, vol. 56, no. 1, p DOI: /TAP [6] KARMAKAR, D. K., ESSELLE, K. P., BIRD, T. S. Wideband micostip leaky-wave antennas with two symmetical side beams fo simultaneous dual-beam scanning. IEEE Tansactions on Antennas and Popagation, 2016, vol. 64, no. 4, p DOI: /TAP [7] WANG, C. J., JOU, C. F., WU, J. J. A novel two-beam scanning active leaky-wave antenna. IEEE Tansactions on Antennas and Popagation, 1999, vol. 47, no. 8, p DOI: / [8] MA, Z. L., JIANG, L. J. One-dimensional tiple peiodic dualbeam micostip leaky-wave antenna. IEEE Antennas and Wieless Popagation Lettes, 2015, vol. 14, p DOI: /LAWP [9] MACHAC, J., POLIVKA, M., ZEMLYAKOV, K. A dual band leaky wave antenna on a CRLH substate integated waveguide. IEEE Tansactions on Antennas and Popagation, 2013, vol. 61, no. 7, p DOI: /TAP [10] DONG, Y., ITOH, T. Substate integated composite ight/lefthanded leaky-wave stuctue fo polaization flexible antenna application. IEEE Tansactions on Antennas and Popagation, 2012, vol. 60, no. 2, p DOI: /TAP [11] JACKSON, D. R., OLINER, A. A., BALANIS, C. (eds.) Moden Antenna Handbook. Hoboken, NJ, USA: Wiley, ISBN-13:

7 RADIOENGINEERING, VOL. 27, NO. 3, SEPTEMBER [12] MACHAC, J., LORENZ, P., SAGLAM, M., et al. Substate integated waveguide leaky wave antenna adiating fom a slot in the boad wall. In 2010 IEEE MTT-S Intenational Micowave Symposium. Anaheim (CA, USA), May 2010, p DOI: /MWSYM [13] POZAR, D. M. Micowave Engineeing. 3 d ed. Hoboken, NJ: Wiley, Ch. 8: Micowave filtes. ISBN: [14] DONG, Y., ITOH, T. Composite ight/left-handed substate integated waveguide and half-mode substate integated waveguide. In 2009 IEEE MTT-S Intenational Micowave Symposium Digest. Boston (USA), 2009, p DOI: /MWSYM [15] WU, K., DESLANDES, D., CASSIVI, Y. The substate integated cicuits a new concept fo high fequency electonics and optoelectonics. In 6th Intenational Confeence on Telecommunications in Moden Satellite, Cable and Boadcasting Sevice TELSKS Nis (Yugoslavia), 2003, vol. 1, p DOI: /TELSKS [16] DONG, Y., ITOH, T. Composite ight/left-handed substate integated waveguide and half mode substate integated waveguide leaky-wave stuctues. IEEE Tansactions on Antennas and Popagation, 2011, vol. 59, no. 3, p DOI: /TAP [17] DESLANDES, D. Design equations fo tapeed micostip to substate integated waveguide tansitions. In 2010 IEEE MTT-S Intenational Micowave Symposium. Anaheim (CA, USA), May 2010, p DOI: /MWSYM [18] About the Authos Rihem NOUMI was bon in Zaghouan, Tunisia. She eceived the degee in Electical Engineeing fom the Faculty of Sciences of Tunis, Tunisia in She is cuently woking towad the Ph.D. degee in Electical Engineeing at the same faculty. He main eseach inteests lie in the LWA antenna designs and SIW technology. Jan MACHAC was bon in Hanice, Czechoslovakia, in He gaduated fom the CTU in Pague in He eceived his CSc. (Ph.D. equivalent) in Electonics in 1982 at the Institution of Radio Engineeing and Electonics of the Czechoslovak Academy of Science in Pague. He eceived his DSc. degee in Radio Electonics in 1996 and was named a pofesso of Electical Engineeing in His main scientific inteests cove investigation of plana passive elements and subsystems of micowave technology, popagation of electomagnetic waves in peiodic stuctues and metamateials. He is the autho o co-autho of moe than 250 publications in scientific jounals, including intenational ones as well as national confeences. Ali GHARSALLAH eceived the degee in Radio Fequency Engineeing fom the Highe School of Telecommunication of Tunis in 1986 and the Ph.D. degee in 1994 fom the Engineeing School of Tunis. Since 1991, he has been with the Depatment of Physics at the Faculty of Sciences of Tunis. Actually, he is a full Pofesso in Electical Engineeing and the Diecto of the Engineeing studies in the Ministy of Highe Education of Tunisia. His cuent eseach inteests include smat antennas, aay signal pocessing, multilayeed stuctues and micowave integated cicuits. He has about eighty papes published in scientific jounals and moe than a hunded confeence papes. Pofesso Ghasallah supevises moe than twenty thesis and fifty Mastes.