Design and Chaacteization of Confomal Micostip Antennas Integated into 3D Othogonal Woven Fabics Xin Wang 1, Lan Yao 1, Fujun Xu 2, Dongchun Zhou 1, Yiping Qiu 1 1 College of Textiles, Donghua Univesity, Shanghai China 2 Key Laboatoy of High-Pefomance Fibes and Poducts, Donghua Univesity, Shanghai CHINA Coespondence to: Yiping Qiu email: ypqiu@dhu.edu.cn ABSTRACT The integation of the antenna and textile mateials is vey impotant in the amy potective o data tansmission clothing. In this study, a novel micostip antenna integated into a 3D othogonal woven fabic was successfully designed and fabicated. This type of antenna is designed to wok in weaable o confomal antenna applications. Simulation wok using HFSS softwae was done fo the detemination of antenna size. Antenna pefomance including etun loss, adiation patten and gain wee measued and the simulated esults wee found to have good ageement with the measued esults. The measued etun loss was -18.32dB with a esonant fequency of 1.75GHz. The gain unde the fequency of 1.70GHz eached as high as 6.47dB. These esults ae consideed to be vey valuable, and this type of integated antenna is expected to be useful as weaable antenna in the telecommunication o smat textile antenna field. INTRODUCTION Since the concept of smat textile systems was intoduced in 1990s, eseach on electo-textile has apidly expanded [1-8]. Nowadays, moe and moe attention has been given to the healthcae and potective clothing sectos [1,7]. In these cicumstances, the antenna, as an electonic element, plays an impotant ole in wieless data tansmission. In ode not to lose the flexibility and comfot of gaments, antennas should be fully integated into the textile mateials. Among all types of antennas, micostip patch antennas, as flat, thin and flexible antennas, seem most suitable fo integation into clothing. A micostip antenna in its simplest configuation consists of a adiating patch on one side of a dielectic substate and a gound plane on the othe. Micostip antennas have seveal advantages compaed with conventional micowave antennas. They have low volume, low pofile plana configuations and low fabication cost. These advantages esulted in the micostip antenna becoming the fist choice in designing electo-textiles. Up to now, many types of integatable textile micostip antennas have been poposed [3, 6] and nealy all of them ae micostip antenna integated textiles [9, 10]. Salonen et al. [6] intoduced textile antennas in which the substate was textile mateial, whee both antenna and gound plane wee made of coppe tape. In this case, the phenomenon of peeling off will exist when the stuctue is subjected to a mechanical load such as impact. In the textile micostip antennas investigated by Hetlee et al. [3], the electo-textile patches wee glued onto the substate and additionally stitched to impove fixing and to pevent an intemediate ai gap. Howeve, continuity of the conductive mateials was damaged using the stitching methods, thus, pobably leading to malfunction of the antenna. In this study, we poposed a micostip-fed micostip antenna woven into a 3D othogonal fabic. Diffeent fom the textile antennas mentioned above, the patch and gound plane wee fully woven with the textile substate using 3D fabic weaving methods. This method was anticipated to esult in supeio integity and impact Jounal of Engineeed Fibes and Fabics 76 http://www.jeffjounal.og
esistance. At the same time, it was felt that the peeling off phenomena could be avoided to a geat extent. Afte fabication, the electical pefomance of the antenna was measued. DESIGN PROCEDURES OF THE ANTENNA STRUCTURE The fundamental design concept of the confomal antenna stuctue is an integal stuctue as shown in Figue 1, in which a micostip antenna is woven into a 3D othogonal fabic. The 3D woven fabic is constucted with thee sets of yans, namely wap, weft and Z-yans, intelaced in thee mutually othogonal diections. Among all 3D fabic stuctues, 3D othogonal woven fabic have the most odeed stuctues and thus can povide an adequate platfom fo the embedded elements [9]. fequency of 1.5GHz using this fabic as the substate. The coppe foils wee glued onto the substate as the patch and gound plane. Then the esonant fequency of the simple antenna was measued using the Vecto Netwok Analyze, and this value was 1.79GHz. The dielectic constant could be finally calculated using Eq. (1). 2 c 1 (1) 2 2 2W f whee c is the velocity of light, W is the width of the patch and f is the esonance fequency of the antenna. Simila methods wee also poposed by Hetlee et al. [3] and seemed to be vey efficient. We obtained the dielectic constant of 3.3. As to the loss tangent, the value of 0.008 is usually used fo this type of fabic. Design of the Antenna The patch size of the woven antenna was calculated accoding to Eq. (2) and Eq. (3). The width of the patch was calculated fom FIGURE 1. The concept of the confomal antenna stuctue: (a) micostip antenna; (b) 3D othogonal woven fabic; (c) scheme of the micostip antenna integated into the 3D woven fabic. Dielectic Constant of the Fabic Substate The antenna was designed to wok at ada L-band with a esonant fequency of 1.5GHz. The substate of the antenna is 3D othogonal woven glass fibe fabic with a thickness of 2.4mm. To detemine the patch size of the micostip antenna, the dielectic constant of substate is equied. The dielectic constant of the woven glass fibe fabic is 3.5, as povided by the manufactue. Howeve, we need to know the accuate value to design the patch size of the antenna. So we fist designed a simple co-axial feeding micostip antenna with a esonant y z x c 1 W 2f 2 1/2 (2) whee c is the velocity of light, f is the esonance fequency of the antenna, ε is the dielectic constant of the substate which has been obtained using the method above. The length of the patch was then obtained fom c L 2 (3) f 2 e whee ε e is the effective dielectic constant and Δl is the line extension. A compute aided design tool, High Fequency Stuctual Simulato (HFSS) povided by Ansoft Copoation, was used to simulate the pefomance of the antenna. The final size of the antenna, shown in Figue 2, was also adjusted by using HFSS. Jounal of Engineeed Fibes and Fabics 77 http://www.jeffjounal.og
FIGURE 2. The size of the antenna (mm). FABRICATION OF THE ANTENNA The specification of glass and coppe yans in the 3D fabic antenna ae listed in Table I. The confomal antenna was woven as a egula 3D othogonal woven fabic as shown in Figue 1(c). In this 3D fabic, glass fibes wee used as the wap, the weft and z yans. In weaving the antenna patch and gound plane pats, the conductive yans in x and y diections wee othogonally woven to fom the gid stuctue. The woven antenna was then soldeed with a feeding connecto. The eal confomal antenna integated into the 3D woven fabic was shown in Figue 3. TABLE I. The specification of glass and coppe yans in the 3D fabic antenna. FIGURE 3. The confomal antenna integated into the 3D woven fabic. RESULTS AND DISCUSSION The etun loss of the simulated and measued values of the antenna is shown in Figue 4. The simulated etun loss is -16.33dB with the esonant fequency of 1.51GHz while the measued etun loss is -18.32dB with the esonant fequency of 1.75GHz. The measued etun loss shifted a little compaed with the simulated one, howeve, it still woks in the ange of 1-2GHz. The measued VSWR (voltage standing wave atio) was calculated as 1.28 fom the etun loss value, which needs the geneal equiement of VSWR below 2 in the antenna pefomance. In addition, the bandwidth of the measued antenna below VSWR<2 is 4.3%, esulting in an adequate bandwidth of this type of the antenna. ANTENNA PERFORMANCE TEST To descibe the pefomances of the antenna, the etun loss and the adiation patten ae the two significant paametes. The eflection coefficient was measued using an 8722ES Micowave Netwok Analyze unde laboatoy conditions, and the etun loss was obtained at Pot 2, with a temination at Pot 1. The adiation patten was measued in the anechoic chambe using HP 8510C Antenna Test System. The antenna was fixed with a temination of the section pot, and then the signal of the vetical polaization was tansmitted to the antenna. The adiation patten was obtained fom the signal eceived by the 360 otating antenna. Gains wee calculated by compaing field values of a efeence-gain log peiodic antenna. FIGURE 4. The simulated and measued etun loss of the antenna. The simulated and measued adiation pattens of the antenna ae shown in Figue 5. It can be seen that the measued esults agee well with the simulated esults. The highest values can be obtained in the 0 degee diection and the font lobe has much lage level than the back lobe in both of the simulated and measued antennas. Howeve, the beam widths of the simulated adiation pattens ae naowe than the measued ones indicating moe Jounal of Engineeed Fibes and Fabics 78 http://www.jeffjounal.og
concentated adiation diection. This is mainly due to the size contol discepancy in the weaving pocess. Theefoe, using thinne fibes and contolling stable size of the patch ae vey impotant, which needs moe attention in the futue manufactuing pocess. FIGURE 5. The (a) simulated E plane, (b) simulated H plane, (c) measued E plane and (d) measued H plane adiation pattens. The measued gains of the antenna ae listed in Table II. The gain in the fequency of 1.70GHz eaches as high as 6.47dB, which needs the geneal gain equiement of this type of antenna. The gain does not each the lagest value at the esonant fequency of 1.75GHz as shown in the measued etun loss the antenna mainly due to the diectivity accuacy fo the woven antenna. In ou pevious pape, how the space atios and woven stuctue would affect the antenna popeties has been discussed [12]. In that pape, the space atio has been detemined as less than 1.7. In this pape, the space atio the 3D fabic antenna was 0.5 which was also less than 1.7 and poved to give pope antenna popeties. In the eal application, this value is enough fo eceiving and enlaging signals. TABLE II. The measued gain of the antenna. CONCLUSIONS A micostip antenna integated in the 3D othogonal woven fabic was successfully fabicated in this study. This type of antenna is aimed to wok fo weaable o confomal antenna applications. The dielectic constant of the 3D fabic substate was fist calculated, which is the pe-equied paamete fo the design of the patch size. The simulated esults of the etun loss and adiation patten showed good ageement with the measued values. The etun loss, adiation patten and gain of the antenna wee in the equied ange of the common single-element micostip antenna. This type of integated antenna is expected to be a weaable antenna applied in the amy telecommunication and othe applications fo smat textile antennas. ACKNOWLEDGMENT This wok was suppoted by the National High Technology Reseach and Development Pogam of China (No. 2007AA03Z101), the State Key Pogam of National Natual Science of China (No.51035003), Natual Science Foundation fo the Youth (No. 50803010 and 60904056), National Science Foundation fo Post-doctoal Scientists of China (No.20100470664), Shanghai Post-doctoal Reseach Funded Poject (No. 09R21410100), the Pogam of Intoducing Talents of Discipline to Univesities (No.B07024), Shanghai Univesity Young Teache Taining Pogam and the Fundamental Reseach Funds fo the Cental Univesities. REFERENCES [1] Gatzoulis L. and Iakovidis I., IEEE Engineeing in Medicine and Biology Magazine 26(5):51(2007). [2] Hetlee C., Rogie H., Vallozzi L., et al., IEEE Tansactions on Antennas and Popagation 57(4):919(2009). [3] Hetlee C., Tonquo A., Rogie H., et al., Textile Reseach Jounal 78(8):651(2008). [4] Januszkiewicz, L., Hausman, S., Kacpzak, T., et al. in 2008 Mikon Confeence Poceedings, Vols 1 and 2, 2008, pp. 377-380. [5] Salonen, P., Keskilammi, M., and Rahmat-Samii, Y. in 2008 Ieee Antennas and Popagation Society Intenational Symposium, Vols 1-9, 2008, pp. 1700-1703. Jounal of Engineeed Fibes and Fabics 79 http://www.jeffjounal.og
[6] Salonen, P., Yang, F., Rahmat-Samii, Y., et al. in Ieee Antennas and Popagation Society Symposium, Vols 1-4 2004, Digest, 2004, pp. 451-454. [7] Vallozzi, L., Rogie, H., and Hetlee, C., Ieee Antennas and Wieless Popagation Lettes 7:440(2008). [8] Vallozzi, L., Rogie, H., and Hetlee, C. in 2009 3d Euopean Confeence on Antennas and Popagation, Vols 1-6, 2009, pp. 967-970. [9] Du, C., Zhong, S., Yao, L., et al. in Poceedings of Intenational Symposium on Signals, Systems and Electonics (ISSSE2010),Vol 2, 2010, pp.662-663. [10] Wang, G., Zhu, C., and Xu, C., Advanced Mateials Reseach 450:175(2011). [11] Bogdanovich, A. E., Wigent, D. E., and Whitney, T. J., Sampe Jounal 39(4):6(2003). [12] Yao, L., Wang, X., Xu, F., et al., Applied composite mateials (online available) DOI: 10.1007/s10443-010-9177-4. AUTHORS ADDRESSES Xin Wang Lan Yao Dongchun Zhou Yiping Qiu Donghua Univesity No. 2999, Noth Renmin Road Songjiang Distict Shanghai, 201620 CHINA Jounal of Engineeed Fibes and Fabics 80 http://www.jeffjounal.og