A Broadband Transmission Metasurface with Polarization-Transforming Functionality

Transcription

1 RADIOENGINEERING, VOL. 6, NO. 4, DECEMBER A Boadband Tansmission Metasuface with Polaization-Tansfoming Functionality Wei CHEN, Jun GAO, Xiang-Yu CAO, Huan-Huan YANG, Zhao ZHANG, Si-Jia LI, Jiang-Feng HAN, Chen ZHANG Infomation and Navigation College, Ai Foce Engineeing Univesity, No.1 Feng Hao Road, Xi an 7177, China 17353@qq.com, gjgj9694@163.com, xiangyucaokdy@163.com, jianye891@16.com, bjzhangzhao33@16.com, lsj51@16.com, ghwewehan@16.com, xue3long@sina.cn Submitted Apil 4, 17 / Accepted July 15, 17 Abstact. A tansmission metasuface with polaizationtansfoming functionalities is pesented. The unit cell is chaacteized by boad band, low pofile and low loss. Due to the asymmetic stuctue, the poposed metasuface shows diffeent esponses to diffeent linea-polaized incidences. Fo a paticula linea-polaized incidence, the polaization diection of tansmitted waves will be otated by 9 in GHz with high polaization convesion atio (PCR). Howeve, fo the othogonal-polaized ones, the incidence will be eflected totally and the polaization emains. The opeating mechanism of the poposed metasuface is analyzed both by theoetical investigations and numeical simulations. Measued esults of the fabicated samples ae in good ageement with the simulated ones. Keywods Metasuface, boadband, polaization-dependent, high polaization convesion atio 1. Intoduction In ecent yeas, the constantly updating communication technology has wondefully advanced the living standads of human beings, and the upcoming 5G mobile communication ea will be fascinating because of its high infomation tansmission ate. Compaed to 4G communication netwok, 5G communication system not only is fa ahead of the ate, but also significantly impoves use density and use capacity based on the polaization isolation chaacteistics of electomagnetic waves. Polaization, as an impotant featue of electomagnetic waves, not only has impotant applications pospects in the field of moden communications, but also in ada, detection, and imaging [1]. Meanwhile, the polaization contol is completely equied in micowave egime, as well as in teahetz, infaed, and visible fequencies []. Theefoe, the eseach of how to manipulate the polaization of electomagnetic wave is in geat demands. The manipulation of the electomagnetic wave by the metamateials nomally aims at the contol of its amplitude [3 6], phase [7 ] and polaization [1 ]. Accoding to the popagation diection of electomagnetic waves, polaization-manipulating metamateials consist of eflective and tansmitting types. Cuently, lots of polaization otating eflective metamateial ae epoted. By using multi-laye cascading [1], metallized via [13], multiple plasmon esonances [14] and othe anisotopic stuctues, many eflective polaization convetos with boadband and high polaization convesion atio pefomance have been successfully pesented. The conventional applications of the eflective polaization-manipulating metamateials include: acting as eflective suface to achieve polaization tansfomation [15] o implement a eflectaay antenna [16], constituting a eflective sceen to educe ada coss section (RCS) [17]. Fo tansmitting ones, it is usually employed as filtes fo waveguide tansmission systems [18], as polaization convetos fo antennas [19] and as antennas tansmitaays to achieving beam focusing, beam steeing and beam shaping []. Howeve, the pecondition fo the application is that these polaization-manipulating metamateials exhibit low loss, high polaization convesion efficiency and low fabication cost. But, how to take all these factos into consideation still emains a big challenge fo the eseaches of polaization convetos. In this pape, a kind of polaization-dependent tansmission metasuface is poposed. In the fequency ange of GHz, the polaization diection of the tansmitted wave will be otated by 9 when a paticula lineapolaized wave iadiates the metasuface. The poposed polaization-tansfoming metasuface is chaacteized by boadband, high efficiency, low loss and low pofile. Because of these noticeable pefomances, the poposed metasuface has potential applications in waveguide tansmission systems and tansmitaay antenna domain.. Stuctue Design The unit cell stuctue of the polaization-tansfoming tansmission metasuface is shown in Fig. 1. The ti- DOI: /e ELECTROMAGNETICS

2 114 WEI CHEN, JUN GAO, XIANG-YU CAO, ET AL., A BROADBAND TRANSMISSION METASURFACE WITH POLARIZATION (c) Fig. 1. Illustation of the pesented unit cell: Schematic of the simulation; the RDSRR; (c) the stipe MG with suface slots paallel to x-axis. layes unit cell consists of a ectangle diagonal-split-ing esonato (RDSRR) stuctue and two othogonal stipe metal gids (MG). The RDSRR, as shown in Fig. 1, is clamped by two substates, and it is employed by achieving polaization convesion. Two othogonal MGs, as shown in Fig. 1(c), ae etched on the suface of the uppe and lowe substate, and ae designed to constitute a Faby-Péot like cavity fo moe efficient polaization convesion [1]. The optimized paametes ae as follows: l1 = 16 mm, l = 1 mm, w = 1.4 mm, w1 = 3. mm, w = 1.8 mm, S1 = mm, S = 1.1 mm, g = 5.9 mm, P = 18 mm. The elative pemittivity of the adopted dielectic is.65. The total thickness of the unit cell is 5 mm, appoximately.1λ at 6 GHz. Duing the designing pocess of the poposed unit cell, Ansoft HFSS 14. is used fo full-wave simulation. Floquet pot and peiodic bounday ae adopted fo a unit cell to simulate an infinite peiodic aay. It is woth noting that the poposed metasuface is chaacteized by polaization-dependent functionalities. When a y-polaized electomagnetic wave iadiates fom the egion 1, the y-polaized incidence can be tansfomed into the x-polaized tansmitted wave. And if the polaization diection of the incident wave is paallel to the x-axis, the x-polaized incidence will be eflected totally, and polaization diection of the eflected wave is also paallel to x-axis. Howeve, when the electomagnetic waves iadiate fom egion, the electomagnetic esponse will be the opposite case. 3. Simulation and Analysis Fo the sake of analysis, we define mn as eflection coefficient, and t mn as tansmission coefficient. Hee x and y epesent the electic field diections of the electomagnetic wave, and m and n denote the diffeent egions. Fo example, t 1 epesents the x-polaized field tansmit- ted into egion when the y-polaized plane wave is incident fom egion 1. The simulation esults ae shown in Fig.. When the y-polaized field is incident fom egion 1, the esults ae shown in Fig.. The cuves manifest that, in the fequency ange of GHz, t 1 is geate than.5 db and t 1 is below 35 db, which indicates that the polaization diection of tansmitted wave is paallel to the x-axis; Meanwhile, it is also obseved that is less than 1 db, and is less than 35 db, which demonstates that the eflected wave is mainly y-polaized. Figue shows the simulation esults of the S paametes when the incidence is x-polaized. It can be seen that is appoximately db. At the same time, both yx and t 1 ae lowe than 35 db and t yx 1 is less than 7 db. These numeical simulations manifest that the x-polaized incident waves will be totally eflected when incident fom egion 1. x Scatteing paametes (db) Scatteing paametes (db) t1 t t1 yx yx t1-1 Fig.. Simulation esults of the S paametes when diffeent polaized wave is incident fom ange 1: y-polaized incidence; x-polaized incidence. y z u v Ei Fig. 3. Schematic of the incident wave: two diffeent coodinate system; decomposition of y-polaized incident wave along u-axis and v-axis. E u E v

3 RADIOENGINEERING, VOL. 6, NO. 4, DECEMBER To explain the opeating mechanism of the metasuface, we otate the -coodinate system by 45 and thus the uv-coodinate system is obtained, as shown in Fig. 3. When the y-polaized incidence popagates along the z-axis, the electic field can be expessed as E i = E i exp(jkz) y. The electic field of the incident wave can be decomposed into two components along u axis and v axis as: Ei Eiexpjkzu Eiexpjkzv. (1) Then the electic field of the eflective and tansmitted wave can be pesented as () and (3), espectively. E uuei expj uu uv i exp j uv kz E kz u vuei expjkz vu vvei expj kz vv, v () Et tuuei expj uu uv i exp j uv kz t E kz u tvuei expjkzvu tvvei expj kzvv. v (3) Reflection coefficient (mag) Tansmission coefficient (mag) uu uv uu vv vv vu uv vu t uu t uv uu vv t vv t vu uv vu Fig. 4. Simulation esults of the S paametes when the incident wave is paallel to u-axis and v-axis: eflection coefficients and phase diffeence; tansmission coefficients and phase diffeence. Phase diffeence (deg) Phase diffeence (deg) Figue 4 shows the S paametes of the element fo u- polaized and v-polaized incidence. As obseved fom Fig. 4, we can conclude that: uu vv 1, uv vu, (4) uu vv, uv vu. As seen fom Fig. 4, we can deive that: tuu tvv t1, tuv tvu t, uu vv, uv vu. By inseting (4) and (5) to () and (3), we can get the eflected field E = E i exp( jkz) y and the tansmitted field E t = t 1 E i exp(jkz) x. In this case, the eflected field emains y-polaized and the tansmitted field is twisted to be x-polaized. This conclusion coincides well with the simulation esults of y-polaized incidence, as shown in Fig.. Similaly, when the polaization diection of incident wave is paallel to x-axis, the eflected field will be E = E i exp( jkz) x, and the tansmitted field is E t = yx 1 E i exp(jkz) y. Theefoe, the x-polaized eflected wave and the y-polaized tansmitted field ae obtained theoetically. Remakably, in this occasion, the x-polaized incident waves will be eflected totally, just as demonstated in Fig.. Figue 5 exhibits the cuent distibution of the RDSRR at fou peak tansmission coefficient fequencies. As the chats show, the RDSRR esembles a pai of symmetical vibatos. At 3.86 GHz, the RDSRR opeates like a pai of half-wave oscillato. At 8.4 GHz, the RDSRR woks coesponding to a pai of full-wave oscillato. Besides, at 4.85 GHz and 6.6 GHz, its opeating states ae between the half-wave and full-wave oscillatos. Accoding to the woking pinciple of the symmetical oscillato, its opeation wavelength depends on the am length of the oscillato. Similaly, the opeation wavelength of the poposed metasuface is closely elated to the size of the RDSRR. So, based on the same pinciple, we can obtain the elationship between the unit's opeation wavelength λ and the am length L (L is the sum of long side and shot side of the RDSRR). The analytical expession can be depicted as.5 L. By calculating, L l1 + w w1 (w1 + w)/.7 mm. Assume the elative pemittivity of the dielectic is denoted by, the opeating fequency ange can be calculated appoximately: c c f. (6) L L The elative pemittivity of the dielectic is.65. So, a (4 8) GHz opeating fequency ange can be obtained accoding to (6). This esult coincides well with the simulation esults. (5)

4 116 WEI CHEN, JUN GAO, XIANG-YU CAO, ET AL., A BROADBAND TRANSMISSION METASURFACE WITH POLARIZATION Fig. 7. The pototype and the measuement setup. (c) Fig. 5. The cuent distibution of the RDSRR at fou peak tansmission coefficient fequencies: 3.86 GHz; 4.85GHz; (c) 6.6 GHz; (d) 8.4 GHz (d) Tansmission coefficient (db) Simulation t Measuement t 1 1 Simulation Measuement Amplitude.6.4. PCR With MGs RR With MGs PCR Without MGs RR Without MGs Fig. 6. The PCR and RR simulation esults of the metasuface with and without MGs. To veify functions of the MGs, we also compae the polaization convesion atio (PCR) and the eflection atio (RR) of the metasuface with and without the othogonal MGs. As shown in Fig. 6, the PCR of the metasuface with MGs is geate than.9 in the fequency ange of GHz. But the PCR of the metasuface without MGs is lowe than.. Besides, in the same fequency ange, the RR of the metasuface with MGs is no moe than.1, while the RR of the metasuface without MGs will be highe than.4. Consequently, it is concluded that the MGs can aise PCR and educe RR significantly. 4. Fabication and Measuement A 4-cell ( ) metasuface pototype is fabicated and measued. The pototype and measuement setup ae illustated in Fig. 7. Duing the measuement, two boadband hon antennas ae utilized as the emitte and the eceive, espectively. When measuing the eflection coefficient, two hon antennas ae on the same side of the sample. When measuing the tansmission coefficient, two hon antennas ae located on eithe sides of the pototype. Reflection coefficient (db) Simulation Measuement - Fig. 8. The S paametes compaison between simulation and measuement esults when the pesented metasuface is iadiated by diffeent polaized incident wave: y- polaized incident wave; x-polaized incident wave. Due to the limited measuement conditions, we have only measued t 1 and of the y-polaized incidence and of the x-polaized incidence. The compaison between the measuement esults and the simulation ones ae shown in Fig. 8. When the y-polaized electomagnetic wave is incident fom the egion 1, the tansmission coefficient measuement esults ae shown in Fig. 8. It is obseved that the measued cuves of the coss-polaization tansmission coefficient t 1 coincide well with the simulation ones in the obseved fequency ange. Howeve, the measuement esult has a slight eo aound 4 GHz. The key eason fo this consequence is that the size of the sample is finite,

5 RADIOENGINEERING, VOL. 6, NO. 4, DECEMBER which is not consistent with the infinite bounday. In addition, the co-polaization eflection coefficient measuement cuve is also consistent with the simulation ones. But the measuement cuve is lowe than the simulation esults aound 6 GHz. By analyzing, the machining eo is the main points fo this consequence. This inevitable facto also esults in the deviation between the measuement and the simulation esults of the co-polaization eflection coefficient aound 6 GHz when the incidence is x-polaized, as shown in Fig. 8. In summay, the measuement esults confim the effectiveness of the design. 5. Conclusion In this pape, a polaization-dependent tansmission metasuface coveing the C band is pesented. The poposed metasuface is chaacteized by low pofile, boadband and high polaization convesion atio. Numeical simulations demonstate that, when a paticula linea-polaized incidence iadiates the poposed metasuface, the polaization diection of the tansmitted wave will be otated by 9 in the fequency ange of GHz. Based on the supeposition pinciple of space wave vecto, we have explained the eason of polaization-conveting function. At the same time, by analyzing the cuent distibution of the RDSRR, we have investigated the opeation fequency ange of the metasuface in detail. Finally, a metasuface pototype is fabicated and measued, and the measuement esults ae in good ageement with the simulation ones. Acknowledgments Authos thank the suppots fom the National Natual Science Foundation of China unde Gant (No , No , and No ). They also thank the eviewes fo thei valuable comments. Refeences [1] SAFARIPOUR, A., BOWERS, S. M., DASGUPTA, K., et al. Dynamic polaization contol of two-dimensional integated phased aays. 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6 118 WEI CHEN, JUN GAO, XIANG-YU CAO, ET AL., A BROADBAND TRANSMISSION METASURFACE WITH POLARIZATION [19] ZARIFI, D., ORAIZI, H., SOLEIMANI, M. Impoved pefomance of ciculaly polaized antenna using semi-plane chial metamateial coves. Pogess in Electomagnetics Reseach, 1, vol. 13, p DOI: 1.58/PIER56 [] PAN, W. B., HUANG, C., MA, X. L., et al. A dual linealypolaized tansmitaay element with 1-bit phase esolution in X- band. IEEE Antennas and Wieless Popagation Lettes, 14, vol. 14, p DOI: 1.9/LAWP [1] GRADY, N. K., HEYES, J. E., CHOWDHURY, D. R., et al. Teahetz metamateials fo linea polaization convesion and anomalous efaction. Science, 13, vol. 34, p DOI: 1.6/science [] PFEIFFER, C., GRBIC, A. Bianisotopic metasufaces fo optimal polaization contol: analysis and synthesis. Physical Review Applied, 14, vol., aticle no. 44. DOI: 1.3/PhysRevApplied..44 About the Authos... Wei CHEN was bon in China, in 1993, and eceived the B.S. degee fom the School of Infomation and Navigation, Ai Foce Engineeing Univesity, China, in 15. Cuently, he is woking towad M.S. degee at the School of Infomation and Navigation, Ai Foce Engineeing Univesity. His eseach inteest is in electomagnetic metamateials and thei antenna applications. Jun GAO eceived the B.Sc and M.A.Sc degees fom the Ai Foce Missile Institute, Xi an, China in 1984 and 1987, espectively. He joined the Ai Foce Missile Institute in 1987 as an assistant teache. He became an associate pofesso in. He is cuently a pofesso of the School of Infomation and Navigation, Ai Foce Engineeing Univesity of CPLA. He has authoed and coauthoed moe than 6 technical jounal aticles and confeence papes, and holds one China soft patent. His eseach inteests include smat antennas, electomagnetic metamateials and thei antenna applications. Xiang-Yu CAO eceived the B.Sc and M.A.Sc degees fom the Ai Foce Missile Institute in 1986 and 1989, espectively. She joined the Ai Foce Missile Institute in 1989 as an assistant teache. She became an associate pofesso in She eceived Ph.D. degee in the Missile Institute of Ai Foce Engineeing Univesity in Fom 1999 to, she was engaged in postdoctoal eseach in Xi an Electon Technology Univesity, China. She was a Senio Reseach Associate in the Dept. of Electonic Engineeing, City Univesity of Hong Kong fom June to Dec 3. She is cuently a pofesso of Telecommunication Engineeing Institute, Ai Foce Engineeing Univesity. She has authoed and coauthoed moe than technical jounal aticles and confeence papes, and holds ten China soft patent. She is the coautho of two books entitled, Electomagnetic Field and Electomagnetic Wave, and Micowave Technology and Antenna published in 7 and 8, espectively. He eseach inteests include smat antennas, electomagnetic metamateials and thei antenna applications, and electomagnetic compatibility.