Two examples of microwave devices, fed by a coplanar waveguide and realized on a thin substrate (or without such a substrate), are employed to investigate the influence of devices’ curvatures and the proximity of different materials on their parameters. To perform the tests, a broadband antenna and a low-pass filter are chosen. A feeding coplanar waveguide is realized on a dielectric material brick attached to an SMA connector and the main device structure is placed in the air or on a thin substrate. The utilization of a thin substrate or its removal from the structure gives rise to the possibility of placing the devices on curved surfaces. The investigated devices are redesigned and manufactured. The antenna has a total size of 46？mm × 44？mm and covers a frequency range of 2.4–35？GHz which gives a 174% fractional bandwidth. The filter has a total size of 50？mm × 80？mm and its bandwidth has a cutoff frequency of 3.4？GHz. The obtained results are verified by measurements and good agreement is achieved. 1. Introduction The microwave components, including antennas and filters, used in mobile devices should not only operate within a specific frequency range but also have a compact and simple structure, with slight dimensions and a light weight. Besides the above requirements, their production costs, especially for large scale production, should also be as low as possible. When the device is designed on a thin and flexible layer, it can be bent and placed on curved surfaces. Conformal components (antennas especially) are becoming popular due to their many advantages and the possibilities of their application [1]. The advantages of using devices with a curved surface arise from the possibility of integrating them with the object on which they are mounted. In the case of conformal antennas, the particular advantage is the increase—relative to the planar antenna—of their visible angular range. The conformal devices find application in a variety of fields, such as airborne, space-borne, ship-borne and missile-borne radar, space vehicles, wireless communication, and sonar. Besides the conformability of the flexible devices, they can find application and are becoming popular in the field of flexible electronics [2, 3]. The main requirements for such devices are light weight, low-cost manufacturing, ease of fabrication, and the availability of inexpensive flexible substrates (i.e., papers, textiles, and plastics). Many flexible antenna structures have been proposed in the literature (e.g., textiles with conducting threads [4] and paper-based [5], fluidic-based [6],
References
[1]
L. Josefsson and P. Persson, “Conformal array synthesis including mutual coupling,” Electronics Letters, vol. 35, no. 8, pp. 625–627, 1999.
[2]
A. Nathan and B. R. Chalamala, “Special issue on flexible electronics technology, part 1: systems and applications,” Proceedings of the IEEE, vol. 93, no. 7, pp. 1235–1237, 2005.
[3]
J. Hu, “Overview of flexible electronics from ITRI's viewpoint,” in Proceedings of the 28th VLSI Test Symposium (VTS '10), p. 84, Santa Cruz, Calif, USA, April 2010.
[4]
S. Zhang, A. Chauraya, W. Whittow et al., “Embroidered wearable antennas using conductive threads with different stitch spacings,” in Proceedings of the 7th Loughborough Antennas and Propagation Conference (LAPC '12), pp. 1–4, Loughborough, UK, November 2012.
[5]
D. E. Anagnostou, A. A. Gheethan, A. K. Amert, and K. W. Whites, “A direct-write printed antenna on paper-based organic substrate for flexible displays and WLAN applications,” Journal of Display Technology, vol. 6, no. 11, pp. 558–564, 2010.
[6]
M. Kubo, X. Li, C. Kim et al., “Stretchable microfluidic radiofrequency antennas,” Advanced Materials, vol. 22, no. 25, pp. 2749–2752, 2010.
[7]
H. R. Khaleel, H. M. Al-Rizzo, and A. I. Abbosh, “Design, fabrication, and testing of flexible antennas,” in Advancement in Microstrip Antennas With Recent Applications, A. Kishk, Ed., InTech, Vienna, Austria, 2013.
[8]
T. A. Denidni and M. A. Habib, “Broadband printed CPW-fed circular slot antenna,” Electronics Letters, vol. 42, no. 3, pp. 135–136, 2006.
[9]
W. Marynowski and J. Mazur, “Design of UWB coplanar antenna with reduced ground plane,” Journal of Electromagnetic Waves and Applications, vol. 23, no. 13, pp. 1707–1713, 2009.
[10]
R. Li, S. Sun, and L. Zhu, “Direct synthesis of transmission line low-/high-pass filters with series stubs,” IET Microwaves, Antennas & Propagation, vol. 3, no. 4, pp. 654–662, 2009.
[11]
E. S. Angelopoulos, A. Z. Anastopoulos, D. I. Kaklamani, A. A. Alexandridis, F. Lazarakis, and K. Dangakis, “Circular and elliptical CPW-fed slot and microstrip-fed antennas for ultrawideband applications,” IEEE Antennas and Wireless Propagation Letters, vol. 5, no. 1, pp. 294–297, 2006.
[12]
Y. F. Liu, K. L. Lau, Q. Xue, and C. H. Chan, “Experimental studies of printed wide-slot antenna for wide-band applications,” IEEE Antennas and Wireless Propagation Letters, vol. 3, no. 1, pp. 273–275, 2004.
[13]
M. E. Bialkowski and A. M. Abbosh, “Design of UWB planar antenna with improved cut-off at the out-of-band frequencies,” IEEE Antennas and Wireless Propagation Letters, vol. 7, pp. 408–410, 2008.
[14]
S.-W. Su, K.-L. Wong, and F.-S. Chang, “Compact printed ultra-wideband slot antenna with a band-notched operation,” Microwave and Optical Technology Letters, vol. 45, no. 2, pp. 128–130, 2005.
[15]
M. Chen and J. Wang, “Compact CPW-fed circular slot antenna for ultra-wideband applications,” in Proceedings of the 8th International Symposium on Antennas, Propagation and EM Theory (ISAPE '08), pp. 78–81, Kunming, China, November 2008.
[16]
K. Chawanonphithak, C. Phongcharoenpanich, S. Kosulvit, and M. Krairiksh, “5.8？GHz notched UWB bidirectional elliptical ring antenna excited by circular monopole with curved slot,” in Proceedings of the Asia-Pacific Microwave Conference (APMC '07), pp. 1–4, Bangkok, Thailand, December 2007.
[17]
D. Kumar, T. Singh, R. Dwivedi, and S. Verma, “A compact monopole CPW-fed dual band notched square-ring antenna for UWB applications,” in Proceedings of the 4th International Conference on Computational Intelligence and Communication Networks (CICN '12), pp. 57–60, Mathura, India, November 2012.
