METAMATERIALS´
Pamplona
21-26 September
2008
Fabric Antennas Integrated with Metamaterials R. D. Seager1, A. Chauraya1, J. C. Vardaxoglou1 and P. deMaagt2 2
1
Loughborough University Electronic and Electrical Engineering Department Wireless Communications Research Group Loughborough Leicestershire, LE113TU Tel: +44 (0) 1509 227 089 Fax: +44 (0) 1509 227 008 United Kingdom
Antenna and Submillimetre Wave Section Electromagnetics & Space Environments Division European Space Agency TEC-EE, Room Da211 tel: +31 71 565 5906 fax: + 31 71 565 4999 PO Box 299 NL 2200 AG Noordwijk The Netherlands
Email:
[email protected]
Abstract Metamaterials have shown distinct advantages in both microwave components and antenna applications. All Search and Rescue (SAR) beacons, for example Personal Locator Beacon (PLB), and Emergency Locator Transmitters (ELT), the frequency of operation will be fixed at 406MHz by 2009. The option to incorporate part of these systems into clothing/rucksack for ease of use and compactness leads to an enhancement of the current system. For PLB systems, an integrated woven antenna is less likely to be damaged by falls, avalanches or other accidents. Metamaterial concepts will be used to provide size reduction, control the antenna radiation characteristics and to minimise the interaction between the wearer and the radiating system [1,2].
1. Introduction Laboratory samples of woven patch antennas for Bluetooth applications have been reported in the recent literature [3]. By using different patch shapes and metamaterial techniques the performance of these antennas can be enhanced at the lower frequency being considered here.
2. Circularly Polarised Spiral Antenna A Circularly Polarised Spiral (CPS) antenna working at 406MHz was designed. This CPS configuration is a derivation from a standard crossed-dipole antenna. It is an important requirement that the antenna structure is compact enough for wearable systems applications. The arms of the dipole have
(a)
(b)
(c)
Figure 1 (a) Geometry of the proposed Spiral Circularly Polarised (CPS) antenna, (b) Predicted Return Loss for 405MHz Spiral Antenna, (c) RHCP for Spiral Cross Dipole Antenna.
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METAMATERIALS´
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21-26 September
2008
been convoluted into spirals to reduce size and to facilitate a simple planar feed. In this case, microstrip has been used, although a balanced line may be more appropriate. The spiral of CPS is 73mm x 73mm (see Figure 1(a) and resonates at 405.25MHz, according to Flomerics' Microstripes Version 7.53. The substrate is a simulated felt with εr = 1.45 and h = 1.5mm. The ground plane is set to be copper. The simulated reflection coefficient for this antenna is shown in Figure 1 (b). The antenna plot at frequency of 405.25MHz is shown for RHCP is shown in Figure 1 (c). Between -60 and +30 degrees the Axial Ratio varies from 3dB to 6dB. Outside this range, it falls off significantly. Predicted directivity and gain of this antenna are 7.3 dBi and 6.9 dBi respectively
2. Metamaterial Arrays We have also investigated the option of implementing the spiral antenna pattern as an element in a metamaterial array. Initially, both 2 x 2 and 3 x 3 arrays have been investigated in a variety of ways. The simulated measurements undertaken are 1. Measurement on the substrate surface with a microstrip line passing above the array [4]. 2. The groundplane was broken and the relevant array was placed in that hole to act as part of the ground plane. Figure 2 shows predicted S parameters for 2 x 2 surface taken using measurements for item 1, and Figure3 show what happens when the planar array for 3 x 3 are moved through the substrate and are placed in a hole in the ground plane. The thinking behind this move is to see how well they behave as a ground plane at resonance.
Figure 2 Scattering Parameters for 405MHz Spiral 2x2 surface
Figure 3. S Parameters for 3x3 surface in ground plane
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4. Fabrication and measured results For laboratory evaluation purposes, a CPS copper antenna was fabricated on felt substrate as shown in Figure 4. The CPS antenna was fabricated on a thin dielectric substrate using wet etching techniques, and pasted on the felt substrate using non-conducting tape. The measured results showed a good match at resonant frequency. However, the antenna’s bandwidth is narrow.
(a)
(b)
Figure 4. (a)Copper Prototype for Spiral Cross Dipole Antenna on a Felt substrate, and (b)measured S11 for Felt Substrate.
4. Conclusion For Search and Resue (SAR) purposes, the final objective is to realise a purely texile and compact antenna. So far we have been able to design a simple and compact antenna operating at low frequency. We have also shown that the spiral antenna pattern can implemented as an element in a metamaterial array to provide size reduction, control the antenna performance and to minimise the interaction between the wearer and the radiating system.
5. Acknowledgement The authors wish to acknowledge the financial support to the project from ESA/ESTEC, The Netherlands and Antrum Ltd, UK.
References [1]
Yang, L., Fan, M., and Feng, Z., A Spiral Electromagnetic Bandgap (EBG) Structure and its Application in Microstrip Antenna Arrays, IEEE Microwave Conference Proceedings, 2005. APMC 2005. AsiaPacific Conference Proceedings Volume 3, 4-7 Dec. 2005 Page(s):4 pp.
[2]
Tse, S., Sanz Izquierdo, B., Batchelor, J.C. and Langley, R.J., Convoluted Elements for Electromagnetic Band Gap Structures, Antennas and Propagation Society International Symposium, 2004. IEEE, Volume 1, Issue , Volume 1, 20-25 June 2004 Page(s): 819 - 822
[3]
I. Locher, M. Klemm, T. Kirstein, G. Trster, “Design and Characterization of Purely Textile Patch Antennas”, IEEE Transactions on Advanced Packaging, Volume 29, Issue 4, Nov. 2006 Page(s):777 -788
[4]
C. B. Mulenga, A. Chauraya, J. A. Flint, and J. C. Vardaxoglou, "Polar Design and Measurement Techniques for Electromagnetic Band Gap Structures”, 2008 URSI General Assembly, Chicago, Illinois, USA, August 7-16, 2008
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