A novel wideband microstrip-fed elliptical slot array antenna for Ku-band applications

REFERENCES Figure 5 1. J.Y. Jan and J.W. Su, Bandwidth enhancement of a printed wide-slot antenna with a rotated slot, IEEE Trans Anten Propag 53 (2005), 2111–2114. 2. J.Y. Jan, C.Y. Hsiang, J.W. Su, Y.T. Cheng, and W.S. Chen, Printed microstrip-line-fed wideband slot antenna with a hexagonal slot, IEEE Int Symp Anten Propag 1B (2005), 569 –572. 3. W.S. Chen and F.M. Hsieh, A broadband design of a printed isosceles triangular slot antenna for wireless communications, Microw J 48 (2005), 98 –102. 4. M.K. Kim, K. Kim, Y.H. Suh, and I. Park, A T-shaped microstrip-linefed wide slot antenna, IEEE Int Symp Anten Propag 3 (2000), 1500 – 1503. 5. H.-D. Chen, Broadband CPW-fed square slot antennas with a widened tuning stub, IEEE Trans Anten Propag 51 (2003), 1982–1986. 6. J.Y. Sze and K.L. Wong, Bandwidth enhancement of a microstrip-linefed printed wide-slot antenna, IEEE Trans Anten Propag 49 (2001), 1020 –1024. 7. N. Behdad and K. Sarabandi, Wideband double-element ring slot antenna, Electron Lett 40 (2004), 408 – 409. 8. Deploying License-Exempt WiMAX Solutions, White Paper, http:// www.intel.com/netcomms/technologies/wimax/306013.pdf. The measured antenna gain of the Antenna 3 © 2006 Wiley Periodicals, Inc. dominant factors in the proposed antenna designs are that of the polygonal slot in terms of ␭g. From that numerical experiment ␭g can be calculated, as be stated in [2]. ␭g ⫽ ␭0 冑␧ r,eff , (2) 1 ⫹ ␧r . 2 Then, the lowest frequency (fL) is formulated in[2], which is relative to a half of the Lperimeter. where ␧r,eff ⫽ fL ⫽ C0 冉 冊 1 L perimeter/ 2 ␧ r,eff Evangelos S. Angelopoulos,1 Argyris Z. Anastopoulos,1 Dimitra I. Kaklamani,1 Antonis A. Alexandridis,2 Fotis Lazarakis,2 and Kostas Dangakis2 1 School of Electrical and Computer Engineering, National Technical University of Athens, 9, Iroon Polytechniou, GR-15780 Zografos, Athens, Greece 2 Institute of Informatics and Telecommunications, NCSR Demokritos, Patriarchou Grigoriou, GR-15310 Ag. Paraskevi, Athens, Greece Received 17 February 2006 1 2 , A NOVEL WIDEBAND MICROSTRIP-FED ELLIPTICAL SLOT ARRAY ANTENNA FOR KU-BAND APPLICATIONS (3) where the C0 is the speed of the light in free space. We found out the optimum case is Antenna 3. Figures 3 and 4 show the measured and simulated radiation patterns of the x–z plane and y–z plane at f ⫽ 2.45, 5.15 GHz for the Antenna 3. In the x–z plane and y–z plane, the good radiation characteristic of the Antenna 3 was shown. The maximum antenna gain of the Antenna 3 is about 5.85 dBi, and the gain variation for the antenna 3 is observed to be less than 1.72 dBi. That the minimum antenna gain of the Antenna 3 is more than 4.1 dBi, it is suitable for Wimax applications. ABSTRACT: This study presents a broadband microstrip slot array structure with a novel feeding technique, which offers enhanced bandwidth and very low cross-polarization levels, targeting the satellite reception application market in the Ku-Band. The single element module and the antenna array formulations of two, four, and eight elements are examined, fabricated, and experimentally characterized. Details of the design procedure and experimental results are discussed. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1824 –1828, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21791 Key words: microstrip-fed array; elliptical; slot; low cross-polarization; Ku-band 1. INTRODUCTION 4. CONCLUSION From the results obtained in this study, the impedance bandwidth for the propose antenna is approximately 104% (1.85–5.84 GHz) for a 2:1 VSWR. The conventional printed wide slot antenna is operating in a bandwidth of the order 10 –20% [3]. Therefore, the result of the novel design is more than five times better than conventional printed wide slot antenna. The proposed Antenna 3 can easily be excited by a 50-⍀ microstrip line printed on the dielectric substrate that material FR-4, and good impedance matching can be obtained for operating frequencies. The proposed design of the antenna with good gain is suitable for Wimax applications. 1824 Printed array antennas are appropriate for salient mobile communications, since they have the advantage of planar configuration, low profile, light weight, and ease of integration with other circuits. Microstrip patch antennas, which are commonly used in array formulations, suffer mainly from narrow bandwidth and secondly from surface wave excitation, while they are strongly dependant on the feeding network. So far, bandwidth enhancement remains a huge challenge, since it ensures higher bit rates, integration of more services in adjacent frequency bands, and less fabrication intolerance. Many techniques have been proposed in order to alleviate the narrow bandwidth limitation. In [1], it has MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 48, No. 9, September 2006 DOI 10.1002/mop TABLE 1 Element Geometrical Parameters of a Single Elliptical Slot Description Ground plane length Ground plane width x axes of the elliptical patch y axes of the elliptical patch x axes of the elliptical slot y axes of the elliptical slot Distance from the microstrip line to the slot Microstrip length Microstrip width Parameter Value (mm) L W L1 R1 L2 R2 dw 15 15 2 3 4 6 1 4 1 been electrochemically etched and experimentally characterized in a fully anechoic chamber facility. Figure 1 Geometry of the proposed elliptical slot antenna been shown that the incorporation of L- and T-shaped slots in microstrip monopole antennas helps in generating additional resonances. In [2], it has been reported that by implementing a fork-like tuning stub over a squared microstrip slot, bandwidth is significantly enhanced. In [3], the authors contacted experimental investigations in various shaped wide-slot antennas being fed by various shaped patch microstrip elements and demonstrated that by choosing suitable combinations of feed and slot shapes, optimum impedance bandwidth can be obtained. In this paper a novel, highly efficient feeding technique for microstrip slot arrays is introduced. The array consists of microstrip lines terminated in elliptical stubs over a similar shaped aperture ground plane (see Fig. 1). The ease of fabrication with the two metallization layers on a single substrate make this module appropriate for direct integration with other single or multi-substrate PCB circuitry. The adopted design philosophy has been partly derived from the work reported in [4], where differential and single ended elliptical antennas have been shown to exhibit ultra wide-band behavior. The antennas reported there can be easily modified and fed by a microstrip line, providing a more stable mass-manufacturable structure. Consequently, elements with this modified microstrip feeding network can be interconnected and form array structures. The above procedure is implemented for the 10 –12 GHz band, which is suitable for satellite reception applications in the Ku-band. However, the authors have reported in [5] that these types of radiators can be tuned to resonate in lower frequencies with ultra wideband performance, therefore exhibiting bandwidths of beyond 120%, with respect to the center frequency of operation. Here we will present slot array topologies of two (2⫻), four (4⫻), and eight (8⫻) elements, which demonstrate measured impedance bandwidth ratios of 44, 25, and 19%, respectively. It can be noted, that the array bandwidth decreases when the number of elements increases, nevertheless it is firmly kept over 2 GHz, but with some shift on the central frequency. Considering the miniature size of the arrays, high gain is achieved with 6.8 dBi for the 2⫻ array, 11 dBi for the 4⫻, and 13.4 dBi for the 8⫻ in the frequency of 11 GHz. By incorporating a ␭g/4 reflecting cavity configuration the gain of the 8⫻ array is upgraded to 15.5 dBi, whereas the undesirable bidirectional radiation is eliminated. The single element and the 8⫻ array with the incorporated cavity have been examined in terms of simulation, while the 2⫻, 4⫻, and 8⫻ array models have DOI 10.1002/mop 2. SINGLE ELEMENT The layout of the single element antenna is illustrated in Figure 1. All models including the single element are developed on a TLC – 30 substrate of 1.575 mm (h) thickness and relative permittivity (␧r) of 3 from Taconic®. The ground plane dimensions are L mm by W mm and the metal cladding is 0.018 mm. The x and y axes of the elliptical ground slot are L2 and R2 respectively, while R1 and L1 are the axes of the terminated microstrip elliptical stub element. The detailed design parameters of this slot antenna are listed in Table 1. As indicated in [4], the distance of the elliptical stub from the similarly shaped aperture ground plane with respect to the feeding point is symmetrically and gradually increasing. As a consequence, the impedance change from one resonant mode to another is small, therefore enabling very large bandwidth. Consequently, the distance from the edge of the microstrip line to the lower end of the elliptical slot (dw) determines the impedance matching. Considering the careful alignment between the two sides of the board during prototyping, dw is refrained from taking extremely small values, that is, less than 1 mm. By fixing dw to 1 mm and by feeding the elliptical stub through a 100 ⍀ microstrip line, the simulated (using HFSS) return loss result, illustrated in Figure 2, exhibits a very satisfactory impedance bandwidth spanning from 8 to 13.7 GHz. The future introduction of the array formulation will detune the central frequency of operation (10.2 GHz) by almost 1 GHz to a higher frequency regime. This will lead to a final Figure 2 Simulated return loss against frequency for the single elliptical slot antenna MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 48, No. 9, September 2006 1825 Figure 5 Geometry of the proposed 1 ⫻ 4 array Figure 3 Geometry of the proposed 1 ⫻ 2 array eight-element array that will widely resonate around 11 GHz. The finally obtained 8⫻ array bandwidth will represent a great percentage of the allocated reception band (10.7⫺12.7 GHz) for satellite applications. 3. ARRAY DESIGN AND CHARACTERIZATION After having optimized the single element antenna in terms of bandwidth, a 1 ⫻ 2, a 1 ⫻ 4, and a 1 ⫻ 8 array have been manufactured using as basis the geometry of the single element. A conventional feeding network is utilized to feed the grounded slots. The feeding network consists of 100 ⍀ transmission lines and L-bends, with T-junctions transforming the 100 ⍀ characteristic impedance microstrip-line (that is being used to feed each radiator) to a 50 ⍀ microstrip line (where a 50 ⍀ SMA connector is soldered), therefore facilitating experimental characterization. We underline that the phase delay for each element in every prototype array configuration is the same, since all the 100 ⍀ microstrip lines have the same length. The same applies to the T-junctions particularly used for the 1 ⫻ 4 and 1 ⫻ 8 prototypes, as will be illustrated in the following lines. This ensures that all elements radiate in phase. width is 32 and 19 mm, respectively. By using a microstrip line of width equal to 1 mm (the equivalent characteristic impedance is 102 ⍀) and length of 5.5 mm, each radiator is being fed by the T-junction that performs the power division with the simultaneous transformation of the characteristic impedance. This array has been characterized in terms of return loss in an HP 8719D network analyzer. The results can be seen in Figure 4. A very satisfactory agreement with prediction can be observed. The obtained bandwidth for the 1 ⫻ 2 array is around 4.5 GHz spanning from 7.5 GHz to around 12 GHz. The calculated gain at 11 GHz is 6.8 dBi, while radiation efficiency within the impedance bandwidth never drops below 93%. 3.1. Array 1 ⫻ 2 Figure 3 illustrates the 1 ⫻ 2 array designed by properly combining two single elements with the feeding network that has been previously described. The centers of the two elliptical stubs were optimally set to a distance of 17 mm, while the overall length and 3.2. Array 1 ⫻ 4 Following the same design concept, four elements were incorporated under a single SMA feed as can be seen in Figure 5. The overall length of the array is almost twice the previous length (66 mm), while width has been increased to 31 mm, owing to the T-junction that performs the power splitting with the same phase delay. The distance between the elliptical stub centers and the length of the 100 ⍀ microstrip line is fixed as 17 and 5.5 mm, respectively (as can be seen in Fig. 3). The 1 ⫻ 4 array prototype and the 1 ⫻ 8 array were both characterized in terms of return loss and radiation pattern behavior in a fully anechoic facility. Figure 6 presents the measured results obtained with a network analyzer. It can be noted that the resonance is gradually shifted towards 11 GHz, while the exhibited impedance bandwidth is ranging from 9.5 to 12 GHz. Radiation co- and cross-polarization measurements of this prototype in x–z Figure 4 Measured and simulated return loss against frequency for the 1 ⫻ 2 elliptical slot array Figure 6 Measured and simulated return loss against frequency for the 1 ⫻ 4 elliptical slot array 1826 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 48, No. 9, September 2006 DOI 10.1002/mop Figure 8 Actual image of the 1 ⫻ 8 array 3.3. Array 1 ⫻ 8 An actual image of the final 1 ⫻ 8 array can be seen in Figure 8. Using the four-element array and by incorporating another Tjunction, the eight-element array was constructed and characterized. The overall dimensions are (134 ⫻ 37) mm2 and the calculated gain at 11 GHz is 13.4 dBi. Figure 9 presents the measured return loss compared to the simulated one. As has been stated earlier, the 1 ⫻ 8 array resonates almost 1 GHz higher than the single module (see Fig. 2). The exhibited bandwidth is approximately 2 GHz, spanning from 10.2 to 12.3 GHz, which represents a great percentage of the Ku-band satellite reception spectrum. It can be noted that impedance bandwidth around 11 GHz is stable to return loss levels values of ⫺25 dB. Future implementations of the array will pursue upgraded impedance characteristics of up to 12.7 GHz (the upper reception limit for satellite reception). Radiation pattern measurements at 11 GHz for this prototype (see Fig. 10) reveal very low cross polarization levels in both principal planes, while the antenna is equally directive for z⫹ and z⫺ directions. Especially for z⫹ axis direction, it should be noted that the adjacent side-lobe levels are at least ⫺13 dB lower than boresight. The bidirectional radiation behavior could be suppressed by using a metallic cavity configuration in the distance of ␭g/4 (⬇4 mm). The cavity will work as a reflective wall, while the planar Figure 7 Radiation pattern measurement versus simulation for (a) x–z plane and (b) y–z plane at 11 GHz for the 1 ⫻ 4 array, ( : co-pol measured, - - - - : cross-pol measured, : co-pol simulated) (H-plane) and y–z (E-plane) at 11 GHz can be seen in Figure 7. Excellent agreement between simulation and measurement can be noticed. The 1 ⫻ 4 array is highly directive with polarization purity in the z⫹ and z⫺ axis (cross-pol levels below ⫺30 dB). Note that the array is more directive with lower side lobe levels for the z⫹ axis direction, nevertheless maximum gain is achieved for z⫺ axis direction. Gain has been calculated to be 11.2 and 8 dBi, for z⫺ axis and z⫹ axis, respectively. DOI 10.1002/mop Figure 9 Measured and simulated return loss against frequency for the 1 ⫻ 8 elliptical slot array MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 48, No. 9, September 2006 1827 ACKNOWLEDGMENT The authors would like to thank Prof. Avaritsiotis and technician Mr. Koliopoulos for the prototype development. Additional credits to Taconic, for kindly providing the microwave dielectric laminates used for implementation of the antennas presented herein. REFERENCES 1. S.I. Latif, L. Shafai, and S.K. Sharma, Bandwidth enhancement and size reduction of microstrip slot antennas, IEEE Trans Antennas Propagat 53 (2005), 994 –1003. 2. J.-Y. Sze and K.-L. Wong, Bandwidth enhancement of a microstripline-fed printed wide-slot antenna, IEEE Trans Antennas Propagat 49 (2001), 1020 –1024. 3. 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 Wireless Propagat Lett (2004), 273–275. 4. J. Powell and A. Chandrakasan, Differential and single ended elliptical antennas for 3.1–10.6 GHz ultra wideband communication, IEEE Antennas and Propagation Symposium, Monterey, CA, June 2004. 5. A.Z. Anastopoulos, E.S. Angelopoulos, D.I. Kaklamani, A. Alexandridis, F. Lazarakis, and K. Dangakis, Circular and elliptical CPW-fed slot and microstrip-fed antennas for ultra wide-band applications, Mediterranean Microwave Symposium, Athens, Greece, September 2005. © 2006 Wiley Periodicals, Inc. SMALL PRINTED MEANDER SYMMETRICAL AND ASYMMETRICAL ANTENNA PERFORMANCES, INCLUDING THE RF CABLE EFFECT, IN THE 315 MHz FREQUENCY BAND Victor Rabinovich,1 Basim Al-Khateeb,2 Barbara Oakley,3 and Nikolai Alexandrov1 1 Tenatronics Ltd., 776 Davis Drive, Newmarket, Ontario, Canada 2 DaimlerChrysler Corporation, 800 Chrysler Drive Auburn Hills, Michigan 3 Department of Electrical and Systems Engineering, Oakland University, Rochester, MI Received 17 February 2006 Figure 10 Radiation pattern measurement versus simulation for (a) x–z plane and (b) y–z plane at 11 GHz for the 1 ⫻ 8 array, ( : co-pol measured, - - - - : cross-pol measured, : co-pol simulated) ABSTRACT: An easily manufactured, reduced size, symmetrical printed meander dipole antenna for remote keyless entry (RKE) automotive applications in the 315 MHz frequency band is proposed. The efficiency and directionality of this symmetrical antenna is estimated and compared with the efficiency and directionality of an asymmetrical antenna. Numerical and experimental results are presented. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1828 –1833, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21790 Key words: short-range communication; printed meander-line antenna; remote keyless entry system configuration and compact size will be maintained. Simulations revealed that bi-directional radiation is eliminated and gain is apparently enhanced to around 15.5 dBi. 4. CONCLUSIONS A novel microstrip array has been designed and experimentally characterized. The single element used to formulate the array is easily reconfigurable in terms of impedance bandwidth. Future implementations will be examined to simultaneously serve transmission and reception mode of modern satellite systems. 1828 1. INTRODUCTION In recent years, the wireless communication market has expanded greatly. Wireless devices such as remote control engine start systems, remote keyless entry (RKE) systems, and automatic tolling systems are now considered “classical ” devices for shortrange vehicle wireless communication [1–3]. Such control and security devices are commonly used in the 315 MHz frequency band in the United States, Canada, and Japan. In these systems, the antenna is a key element in determining system size and perfor- MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 48, No. 9, September 2006 DOI 10.1002/mop