Design of 8 x 8 microstrip Planar Array Antenna for Satellite Communication

Transcription

1 Design of 8 x 8 microstrip Planar Array Antenna for Satellite Communication Dileswar Sahu. Amarendra Sutar. Purnendu Mishra MTech (EIS),MITS,Rayagada E&TC,Dept,BEC,BBSR ECE,Dept,NIST,BAM dileswar_sahu@rediffmail.com sutar_09@yahoo.co.in purnendumishra79@gmail.com Abstract : Observations of wind velocity profiles are very important for studying meteorological phenomena and weather forecasting. Atmospheric radar is one of the most suitable remote sensing instruments for observing height profiles of three components of wind velocity vector, including the vertical velocity with time and height resolutions without influence of weather conditions. Propagation of radar signals through the atmosphere is strongly dependent on local meteorological conditions, especially in the atmospheric boundary layer. The wind profiling radar uses naturally occurring fluctuations in the radio refractive index and precipitation as targets. Due to their small apertures, UHF profilers operating around MHz are most suitable for measuring the winds in the boundary layer and lower troposphere regions. Unlike the VHF wind profiling radars, UHF radars are very sensitive for hydrometeors due to small wavelength. Therefore these profilers are very much useful in studying convection, precipitation etc. UHF radar is a potential tool to carry out research studies such as ABL Dynamics (Winds, Turbulence structure), seasonal and Inter-annual variations, Interaction between the ABL and the free troposphere, precipitating systems, Bright band characterization Rain/cloud drop size distribution etc. It is also useful in the operational Mountain meteorology and civil aviation and identification of atmospheric ducts. It also acts as a supplementary tool to large VHF MST radars by providing the atmospheric data in 0-5 Km height range. 1. INTRODUCTION Observations of wind velocity profiles are very important for studying meteorologicalphenomena and weather forecasting. Atmospheric radar is one of the most suitable remote sensing instruments for observing height profiles of three components of wind velocity vector, including the vertical velocity with time and height resolutions without influence of weather conditions [1]. Propagation of radar signals through the atmosphere is strongly dependent on local meteorological conditions, especially in the atmospheric boundary layer [2] [3]. The wind profiling radar uses naturally occurring fluctuations in the radio refractive index and precipitation as targets. Due to their small apertures, UHF profilers operating around MHz [4][5] are most suitable for measuring the winds in the boundary layer and lower troposphere regions[6]. Unlike the VHF wind profiling radars, UHF radars are very sensitive for hydrometeors due to small wavelength [4]. Therefore these profilers are very much useful in studying convection, precipitation etc. UHF radar[4] is a potential tool to carry out research studies such as ABL Dynamics (Winds, Turbulence structure), seasonal and Inter-annual variations, Interaction between the ABL and the free troposphere, precipitating systems, Bright band characterization Rain/cloud drop size distribution etc. It is also useful in the operational Mountain meteorology and civil aviation and identification of atmospheric ducts. It also acts as a supplementary tool to large VHF MST radars by providing the atmospheric data in 0-5 Km height range [5]. Several UHF radars [4] are being operated across the globe either as research tools or as a part of wind profiler networks for operational meteorology. Atmospheric radars originally developed in 1970s for the research of mesosphere and stratosphere have been extensively applied to operational use for observations of the troposphere wind fields [7] since 1990s as demonstrated by the wind profiler demonstration network. In Japan, more than ten profilers including the MU (middle and Upper atmosphere) radar of Kyoto University have been operated for research use. Through the research and evaluation of profiler s data on the numerical weather prediction (NWP) models, JMA (Japan Meteorological Agency) established the operational wind profiler network and data acquisition system (WINDAS) for the enhancement of capability to watch and predict severe weather in Japan. The network consists of forty 1.3 GHz wind profiling radars which are located across Japan. In India, UHF profiler was established at Gadanki-Tirupati under Indo-Japanese collaboration program. The system, operating since 1997, has provided valuable data to characterize the boundary layer dynamics, precipitation events, bright band and several other aspects of the lower atmosphere. Recently some serious operational difficulties are faced by the system due to aging. Since this system is proved to be a potential tool for atmospheric research, NARL decided to build a new state-of-the art UHF wind profiling radar to continue the research work. UHF wind profiling radars have several applications such as studies of low-level transport of water vapor (For example, by trade winds), boundary layer

2 convergence, frontal passages, lowaltitude turbulence, Global climate change studies, and vertical profiles of precipitation. Operational uses include air pollution prediction, wind shear monitoring, temperature profiling in the radio acoustic sounding system (RASS) mode, Aviation operations, Mesoscale meteorological forecasting, Defense operations,forecast fire management, Weather modification and offshore, shipboard and airborne platforms.uhf wind profiling radar is a potential tool for atmospheric research as well as for meteorology. These radars were developed by companies like radian (Vaisala), Mitsubishi, Miesei, ATRAD, Prosensing, Degreane etc; in collaboration with research laboratories like NOAA, University of Massachusetts, yoto University,CRL, Adelaide University, CNRS/CETP etc. 2. OBJECTIVES OF THE SYSTEM The objectives of the proposed UHF wind profiling radar are multi-fold. The present UHF radar at NARL was installed by CRL-MEC, Japan under the Indo-Japanese collaboration program in the year The system is getting aged and has many operational difficulties. As the collaboration period is over, CRL has replaced the controlling and data processing subsystems to make the system operational. The RF/IF and antenna systems also are giving operational problems; alternative wind profiling radar has been developed for continuing the research in the lower atmosphere.` India has ot expertise in developing the radars for atmospheric research. A 53MHz MST radar, 400MHz ST radar at IITM Pune, and S-band Doppler weather radar at SDSC SHAR Sriharikota have been developed. A UHF wind profiling radar is yet to be developed in INDIA. In recent times the necessity of this system is felt by several research and operational agencies for civilian and strategic applications. The proposed system will be a potential tool to probe the lower part of the atmosphere, which is very much related to weather and climate. The existing system at NARL is proved to be a potential research tool for studying the dynamics of the lower part of the atmosphere. The proposed research applications are listed below. Supplements MST radar Atmospheric Boundary Layer (ABL) Dynamics (Winds, Turbulence structure) Seasonal and Inter-annual variations Interaction between the ABL and the free troposphere Precipitating systems Bright band characterization Rain/cloud drop size distribution Identification of Atmospheric ducts. Scientific Specifications of the Proposed System Mode of operation : Doppler Beam swinging Technique Minimum range : 100m Maximum range : 6 Km (Clear air) Km (Precipitation) Range resolution : 30 m up to 3 Km,100m up to 6 Km Measured parameters : Moments and U, V, W Time resolution : 5 minutes per profile. The beam width requirement for the wind profiler is about 4-5 degrees. To achieve this beam width the antenna aperture size should be at least 11λ. The maximum scan angle is about 20 degrees, which requires an inter-element spacing of 0.7λ. An array of 16X16 or more elements will satisfy these requirements. The following options are considered, 1. 16X16 Active Array Antenna with 256 numbers of 10-watt TRMs X16 Butler beam forming array with 256 numbers of 10-watt TRMs X24 or 16X16 array with Row/Column feed with 24/16 numbers of 100/250-watt TRMs. By considering merits and demerits of all the three types, Butler Beam Forming feed array is chosen for the present radar since it is satisfying all the requirements without much complexity. The TRMs will be placed between the array and butler feed network. Each antenna element will be fed by a 10- watt TRM. 2. METHODOLOGY The designed antenna is an 8X1 linear array. The first step in the design is to specifythe dimensions of a single microstrip patch antenna. The patch conductor can be assumed at any shape, but generally simple geometries are used, and this simplifies the analysis and performance prediction. Here, the halfwavelength rectangular patch element is chosen as

3 the array element (as commonly used in microstrip antennas) [9].Its characteristic parameters are the length L, the width w, and the thickness h, as shown in Figure 1. To meet the initial design requirements (operating frequency = 1.28 GHz, and beam width = 90) various analytical approximate approaches may be used. Here, the calculations are based on the transmission line model [12]. Although not critical, the width w of the radiating edge is specified first. The square-patch geometry is chosen since it can be arranged to produce circularly polarized waves. In practice, the length L is slightly less than a half wavelength (in the dielectric). The length may also be specified by calculating the half wavelength value and then subtracting a small length to take into account the fringing fields [15-17], as; Fig.1 shows the geometry of the proposed 8x8antenna array fed by corporate feed network connected to a 50 ohm feed line on one side of the FR4 substrate of thickness 0.15mm, a dielectric constant of 4.4 and the ground on the other side of the substrate. Corporate feed network is used for power division between antenna element. The amount of power delivered to each patch element is controlled by altering the width of the line and maintaining the length equal. Width of the transmission lines are calculated based on the line impedance. Corporate feed network can also introduce phase change that required for beam steering [7]. Here the corporate feed network is designed for power division. The antenna proposed for this array is the inset fed microstrip antenna. The inset impedance for the antenna is chosen in such a way that it is less than the radiation resistance of the antenna and also it overcomes the practical difficulty of fabrication[8].theoretical design of antenna was done using transmission line model method [9][10]. Analyses were carried out for the 4x4 and 2x2 array also and the geometry is shown in Fig.2 and Fig.3. The substrate thickness of 0.15 mm is chosen so that it can be integrated with the MMIC s. The antenna dimension remains the same for all the three arrays. The dimensions of the radiating element are mm and mm for resonant frequency of 60 GHz. The spacing between the radiating structures is 0.64λ. The inset impedance of the antenna is chosen as 200 ohms for constructing corporate feed network. The dimensions of the transmission lines used in 8x8 array are of widths mm, mm,0.1327mm and mm and length 0.5 mm,0.7478mm, 0.72mm and 12.86mm for 200 ohm,141.4 ohm, 100 ohm and 50 ohm transmission lines. The 50 ohm feed can be microstrip transmission line feed or coaxial feed based on its application. In this paper we have chosen microstrip transmission line feed for integrating with millimeter wave receiver circuits [11]. The designed array structure was simulated using IE3D tool. Figure 1. Geometry of 8x8 Microstrip antenna array with corporate feed network

4 Table 1. Design parameters of 2x2, 4x4 and 8x8 Microstrip antenna array for frequency 60 GHz, dielectric constant 4.4 and substrate thickness 0.15mm. Array/Dimension 2 x2 4x 4 8x8 Length of the patch mm mm mm Width of the patch mm mm mm Inset impedance feed 200ohm 200 ohm 200 ohm Figure 2. Geometry of 4x4 Microstrip antenna array with corporate feed network No.of antenna elements Substrate dimension 25.72x25.7 mm x12.9 mm x6.52m m 2 Feeding Technique Corporate Corporate Corporate Width of the 50ohm line mm mm mm Length of the 50 ohm 12.86mm 6.46mm 3.26mm Figure 3. Geometry of 2x2 Microstrip antenna array with corporate feed network 3. RESULTS AND DISCUSSION The proposed geometry is simulated using IE3D. The performance parameter of the 2x2, 4x4 and 8x8 Microstrip array antenna are compared in Fig.4 and simulation results listed in Table 1. The radiation pattern of the arrays are shown in Fig. 5. It clearly depicts that by increasing the number of elements in the array, the gain and directivity increases with decrease in the beam width. The 8x8 array as a maximum gain of dbi and directivity

5 of 22.4 dbi. and beam width of deg which satisfies the requirement for short range indoor wireless applications. Because of its compactness, it can also be integrated with the existing MMIC s. If further enhancement in gain and beam width is required, we can go for 16x16 array and 32x32 array with similar design concepts. Figure 4a. Return Loss Characteristics of 2x2, 4x4 and 8x8 Microstrip antenna array Figure 4c. Directivity Vs Frequency of 2x2, 4x4 and 8x8 Microstrip antenna array Figure 4b. Gain Vs Frequency of 2x2, 4x4 and 8x8 Microstrip antenna array Figure 4d. Elevation angle Vs Gain of 2x2, 4x4 and 8x8 Microstrip antenna array.

6 Figure 4. Comparison of 2x2, 4x4 and 8x8 Microstrip antenna array performance parameter. Table 2. Simulated results of 2x2, 4x4 and 8x8 Microstrip antenna array. Arrays/ parameters 2x2 array 4x4 array 8x8 array Return loss db db db Bandwidth GHz GHz GHz Gain dbi dbi dbi directivity dbi dbi dbi 3dB width Beam deg deg deg Figure 5b. Radiation pattern of 4x4 array. Beam width deg Figure 5a. Radiation pattern of 2x2 array Beam width deg Figure 5c. Radiation pattern of 8x8 array. Beam width deg

7 CONCLUSION An 8X8 element array has been realized for wind profiling radars. It consists of a single layer narrow band antenna element based on this 8X8 element array was designed. Gain, Bandwidth and radiation patterns have been computed over a frequency at 60 GHz. From the data analysis, it has been pointed out that the side lobe level is the most critical factor, and thus determines the operating bandwidth. However, considering the impedance, gain and maximum side lobe at 60GHz frequency, with GHz bandwidth has been obtained. REFERENCES [1] Balanis, C.A. (1997). "Antenna Theory: Analysis and Design." 2nd ed.new York: John Wiley and Sons, Inc. [2] Y. Kim and D. L. Jaggard, The fractal random array, Proc. IEEE,vol. 74, pp , Sept [3] D. L. Jaggard and T. Spielman, Triadic cantor target diffraction, Microwave Opt. Technol. Lett., vol. 5, pp , Aug Y. Kim, H. Grebel, and D. L. Jaggard, Diffraction by fractally serratedapertures, J. Opt. Soc. Amer., vol. 8, no. 1, pp , Jan [4] D. L. Jaggard, On fractal electrodynamics, in Recent Advances in Electromagnetic Theory, H. N. Kritikos and D. L. Jaggard, Eds. NewYork: Springer-Verlag, 1990, pp [5] H. O. Peitgen, H. J urgens, and D. Saupe, Chaos and Fractals. New York: Springer-Verlag, [6] M. F. Barnsley, R. L. Devaney, B. B. Mandelbrot, H. O. Peitgen, D. Saupe, R. F. Voss, Y. Fisher, and M. Mc Guire, The Science of FractalImages. New York: Springer-Verlag, [7] C. Puente-Baliarda, and R POUS, Fractal design of multiband and low side-lobe arrays, IEEE Trans. On Antennas and Prop., vol.ap-44, May 1996, pp