The frequency reconfigurable volumetric PIFA 
presented in this paper is designed to switch between two US 
public-safety bands, one operating at 700MHz and the other 
having a bandwidth of 17% around 850MHz -  in effect covering 
a range from 800MHz to  900MHz. The reconfigurability is 
limited to only the ground and patch layers as an aim to 
minimize the number of MEMS switches used. The radiation 
pattern of the antenna maintains its shape and the maximum 
gain over this reconfigurable band of operation, 700 – 900 MHPostprint (published version

Centiner, Bedri Artug

Damgaci, Yacine

Jofre Roca, Lluís

Khoshniat, A.

Mopidevi, H.

Rodrigo López, David

English

UPCommons. Portal del coneixement obert de la UPC

 MEMS INTEGRATED RECONFIGURABLE ANTENNA FOR COGNITIVE PUBLIC SAFETY RADIOS    A. Khoshniat1, H. Mopidevi1, Y. Damgaci1, D. Rodrigo2, L. Jofre2 and B. A. Cetiner1, 1ECE Dept, Utah State University, Logan, Utah – 84321, USA  1ali.kh@aggiemail.usu.edu,1bedri@engineering .usu.edu  Universitat Politecnica de Catalunya, Barcelona, SPAIN 2rodrigo@tsc.upc.edu,2 luis.jofre@upc.edu  Abstract— The frequency reconfigurable volumetric PIFA presented in this paper is designed to switch between two US public-safety bands, one operating at 700MHz and the other having a bandwidth of 17% around 850MHz -  in effect covering a range from 800MHz to 900MHz. The reconfigurability is limited to only the ground and patch layers as an aim to minimize the number of MEMS switches used. The radiation pattern of the antenna maintains its shape and the maximum gain over this reconfigurable band of operation, 700 – 900 MHz I. INTRODUCTION The Public Safety community (police, firefighters, etc) in controlling natural or human-caused catastrophes requires a robust, low-cost, cognitive wireless communication system. Interoperability, which enables interoperable communication among various emergency personnel, is also a key concern. The antenna presented in this paper, is to provide a spectrally efficient, low-cost, robust, and compact solution to the interoperability, adaptability, and reliability needs of public safety wireless communications systems. In general, PS community needs to provide voice, data, and video communications across different PS bands – 150, 400, 700, 800, 900 and 4900 MHz The interoperability between two bands - one operating at 700MHz and the other covering a range from 800MHz to 900MHz (conveniently named as mode1 and mode2 respectively), is achieved by a reconfigurable antenna [1] which uses MEMS DC-contact series type switches. Section II describes in brief the type and design of antenna used individually in the two modes. Section III explains the reconfigurability between the two modes. Finally, sections IV and V illustrate the challenges in reconfiguring and the results of the design, respectively. At this stage of our ongoing work, for simplicity, the MEMS are replaced by ideal short and open strips for the two modes and from the previous experience it is understood that introduction of the real architecture of MEMS in the design does not cause a significant change in the operational frequency. II. TYPE OF ANTENNA  Planar Inverted F Antenna (PIFA) [2] popularly used in mobile communications, is used individually for each mode as it reduces the size of the patch to half when compared to the microstrip patch antenna. This half-size reduction is due to the shorting plane used in the antenna structure. Two bandwidth enhancement techniques of PIFA namely T-shaped ground-plane [3] and patch tapering [4] are combined and optimized. Quartz is the dielectric substrate (εr = 3.9, tanδ = 0.0002) and feeding is through coaxial cable. A capacitive coupling [5] is used in conjunction to coaxial cable to decrease the inductance effect thereby increasing the matching over a wider frequency range. For the purpose of further reduction of size of PIFA we use a slit etching technique to increase the electrical path length of the surface current and the slit is L-shaped located on the patch layer. A volumetric antenna employing all these techniques is shown in Fig. 1. The effect of including different techniques in the same design to achieve better results lead to an increase in the number of design parameters in each mode.                        Fig. 1 2 & 3D overview of the volumetric PIFA  All the layers are separately optimized and the final design is obtained. The design methodology described in this section is employed individually for both the modes.   III. RECONFIGURABLE PIFA  The number of MEMS switches used to reconfigure between different modes is directly proportional to the complexity of the design, the reason being the difficulty in placing and subsequent fabrication of the bias lines of each MEMS switch. Hence, our goal is to reduce the number of MEMS switches in the over-all design. For this reason, frequency reconfigurability in the final design is constrained only to the ground plane and radiation patch layers while fixing the dimensions and the location of the coaxial-feed, L-shaped slit and the capacitor patch. Mode2 is designed first as it is targeted to span over a wider frequency range covering 800MHz to 900MHz and then mode1 is obtained by extending the size of radiation patch and the ground-plane.             Fig. 2 Overview of the different layers of reconfigurable volumetric PIFA    The design methodology of the frequency-reconfigurable antenna switching between modes 1 and 2 is described in the Figures 2-4.  Fig. 2 gives the overview of all three layers of the reconfigurable antenna namely ground-plane, radiation-patch and capacitive patch. The hatched area in Fig. 3 and Fig. 4 indicates that the layer is connected to the feed and the switches are on. Table I explains role of MEMS switches in reconfiguring between different modes. The ground-plane size is dominating which can be seen from the figure and the border in Fig. 3 indicates the patch size relative to the ground plane. Gi and Pi represent the switches used in the ground plane and radiation patch respectively, as illustrated in Figures 3 and 4. In Fig. 3 and Fig. 4 the switches are indicated only in one mode to avoid redundant detail and for the sake of clarity, the actual shape of MEMS switch and the width of the long metallic strips are exaggerated from their original dimensions.                                   Fig. 3 Reconfigurable ground layer                Fig. 4 Reconfigurable radiation patch layer   Switch mode1 mode2 Gi=1to16 on off Pi=1to3 on off    Table I Switch Operation  IV. CHALLENGES IN THE DESIGN   As the PIFA operates at a low frequency, i.e., in a range of 700 MHz to 900 MHz and also due to the small gap (0.5mm) between the two ground planes (or the two radiation patches corresponding to modes 1 and 2) to facilitate the MEMS, the coupling effect between the two modes is significant, which is a major design challenge. To alleviate this challenge, we increased the gap between the two ground planes (or radiation patches) and placed a long narrow metallic strip (made of the same material as the radiation patch) which is connected to the other ground-plane (or radiation patch) by small MEMS switches as shown in Figures 3 and 4. This method significantly decreased the coupling effect and improved the result. The final dimensions in mm of the optimized reconfigurable layers of the PIFA are shown as follows for easy representation: (mode1, mode2) - radiation patch (45.5 x Ground layer Radiation Patch layer Capacitive Patch layer G1 G2 G3 G4 G5 G6 G7 G8 G9 G10 G11 G12 G13 G14 G15 G16 mode1 mode2 P1 P2 P3 mode1 mode2 61, 35.5 x 51); overall ground plane size (121x 101, 101 x 81); width of the T-shape, W – (26, 10); and parameter Wt – (12, 2) as shown in Fig. 1. The long metallic strips are 8 mm x 0.5 mm; the height of the substrate h = 10mm and the MEMS switches are approximated by 0.5mm x 0.2 mm metallic strips in Fig. 1.  V. RESULTS The reflection coefficient of the reconfigurable PIFA in mode1 and mode2 is depicted in the Fig. 5. Mode1 has a bandwidth of 22% at 700 MHz and mode2 a bandwidth of 17% at 850MHz for reflection coefficient less than -8 dB. Fig. 6 clearly shows that the radiation pattern (in  = 00 and  = 900 planes) of the designed antenna maintains its integrity and the maximum gain is about 3dB irrespective of the mode of operation. These results correspond to hfss simulations and further investigation in fabrication, test and measurement needs to be done in the future.                                          Fig. 5 Reflection Coefficient of modes 1 and 2                                               a)   = 00                                             b)   = 900   Fig. 6 Radiation patterns of the antenna in two modes  VI. CONCLUSION The designed frequency reconfigurable PIFA operating in the bands 700 MHz and 800 MHz to 900 MHz with minimum number of switches suits well to the interoperable communication needs of Public Safety personnel in times of emergencies. ACKNOWLEDGMENT This project was supported by Award No. 2007-IJ-CX-K025 and Award No. 2009-SQ-B9-K005 awarded by the National Institute of Justice, Office of Justice Programs, US Department of Justice. The opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the Department of Justice. REFERENCES [1] B. A. Cetiner, et al., “Multifunctional Reconfigurable MEMS Integrated Antennas for      Adaptive MIMO Systems,” IEEE Comm. Magazine, Vol. 42, No. 12, pp. 62-70, 2004 [2] K. Hirasawa and M. Haneishi: Analysis, Design, and Measurement of Small Low Profile Antennas, Norwood, MA: Artech House, 1992. [3] F. Wang,  Z. Du, Q. Wang and K. Gong: “Enhanced-bandwidth PIFA with T-shaped ground plane,” Electronics Letters, Vol. 40, No. 23, 1504- 1505 [4] C.K. Byung, D.P. Ju and D.C. Hyumg: “Tapered type PIFA design for mobile phones at 1800 MHz,” Vehicular Technology Conf., Orlando, FL, USA, 2003, Vol. 2, pp. 1012–1014 [5] G. A. E. Vandenbosch: “Capacitive matching of microstrip antennas,” Electron. Lett., vol. 31, no. 18, pp. 1535–1536, 1995.  0.5 0.6 0.7 0.8 0.9 1 1.1 1.2-16-14-12-10-8-6-4-20Frequency (GHz)Reflection Coefficient (dB)  mode1mode250-5-10-15-2004590135180225270315 f = 700 MHzf = 800 MHzf = 900 MHz50-5-10-15-2004590135180225270315 f = 700 MHzf = 800 MHzf = 900 MHz

Mems integrated reconfigurable antenna for cognitive public safety radios

The frequency reconfigurable volumetric PIFA 

presented in this paper is designed to switch between two US 

public-safety bands, one operating at 700MHz and the other 

having a bandwidth of 17% around 850MHz -  in effect covering 

a range from 800MHz to  900MHz. The reconfigurability is 

limited to only the ground and patch layers as an aim to 

minimize the number of MEMS switches used. The radiation 

pattern of the antenna maintains its shape and the maximum 

gain over this reconfigurable band of operation, 700 – 900 M

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Mems integrated reconfigurable antenna for cognitive public safety radios

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