Novel Approach of Phased Array Antenna with Beam Steering Technology for Microwave Power Transmission from SSPS System Golap Kanti Dey 1, Kazi Tanvir Ahmmed 2, Rubell Sen Goopta 1 1 School of Engineering and Computer Science, Chittagong Independent University, Chittagong-4000, Bangladesh. 2 Department of Applied Physics, Electronics & Communication Engineering, University of Chittagong, Chittagong-4331, Bangladesh Email: golap@ciu.edu.bd, tanvir@cu.ac.bd, rubellsen@ciu.edu.bd Abstract- This paper represents design methodology of novel phased array antenna and its radiation pattern of 100 elements linear phased array for highly efficient microwave power transmission (MPT) which will be focused on ground based receiving station for microwave power transmission from Space Solar Power Satellite (SSPS) system. Taking different ratio between antenna element spacing, d and wavelength, λ we studied radiation pattern of phased array antenna for proposed 2.45 GHz microwave power input. Phased array antenna is a multiple-antenna system, the prominent part of SSPS system, in which the radiation pattern can be reinforced in a particular direction and suppressed in undesired directions by steering electronically in the microwave power transmission from SSPS system. Keywords Phased Array Antenna, Array Construction, N- element phased array, Radiation Pattern etc. I. INTRODUCTION Antenna is a dominant technology required for Solar Power Satellite system. Solar power satellite (SPS) [1] is a renewable and infinite energy system which works in the Geostationary Earth Orbit as an electric power plant in space. Main theme of solar power satellite is that SPS will collect solar energy, converts sunlight to electricity and beam the power to ground-based receiving stations. Among the four main parts of microwave power transmission (MPT) for SSPS system, antenna is prominent part where we are proposing the noble phased array antenna (PAA) for reinforcing the radiation pattern precisely and accurately. All kinds of antennas can be applied as a radiating part for MPT system, as for example, parabolic antenna, microstrip antenna, Yagi-Uda antenna, horn antenna etc. However to control a microwave beam direction accurately and precisely, we have to use a phased array antenna system. Phased array antennas [2] consist of multiple fixed antenna elements to reinforce the radiation pattern in a specific direction with suppressing the undesired one. Relative phase, amplitude applied to each radiating element are used to determine the shape and direction of radiation pattern. By using the phased array antenna we can steer the beam pattern electronically. By controlling the amplitude and phase of each element individually beam pattern of the array can be formed to be more generalized. Beamforming by using this technique can be used to suppress side lobes, by creating the patterns of radiation to the specific direction. From the several decades phased arrays have been traditionally used in military applications.. Increasing interest has drawn in utilizing phased array technology for commercial applications after recent growth in civilian radar-based sensors and communication systems. Hsi-Tseng Chau [3] designed a methodology of a phased array antenna whose radiation will focus in the near zone of array aperture by using microstrip feeding circuits. Takenori Yasuzumi [4] worked on new type of phased array antenna using bi-layered microstrip antenna (MSA) composed by 3-patch element. Reference [5] proposed a measurement method that can reduce measurement time for phased array antenna while providing all radiation patterns and a fixture to measure the 3-D radiation pattern which is compact and provides low interference on antenna s radiation pattern. Naoki Shinohara [6] did their experiment for Microwave Power Transmission with an advanced phased array system to make experiments on beam forming with phased array. Finite difference time-domain method to the generalized analysis of phased array antennas [7] also presented by Gregory M. Turner. Low-profile. Highsensitivity receiving sub-array module [8] with hightemperature superconducting filters for an active phased array antenna also developed by Hiroyuki Kayano. Latest research work has been going on to use phased antenna in the wireless power transfer. In this research work we are going to depict phased array antenna system to transfer microwave power which is the significant part of SSPS system. In our research work we are presenting the uniform linear phased array system with the radiation pattern for 100 elements where proposed microwave power input is 2.45 GHz for SSPS system. We have also depicted radiation patterns by
varying ration between the distance of the element and wavelength. Linear arrays are designed to produce a narrow beam of main lobe keeping side lobes small as far as possible. The primary reason for using phased array is to produce a directive beam that can be repositioned (scanned) electronically. II. PHASED ARRAY CONSTRUCTION Phased array antenna is a directive antenna system consist of multiple fixed antenna elements with individual radiating sources feeding coherently and use alterative phase or timedelay control at each element to reinforce the radiation pattern to predefined angles in a particular direction. For pattern shaping sometimes variable amplitude control is also provided. However, the fundamental reason for using phased arrays is to generate beam pattern that can be steered [9] by means of electronic control system. Block diagram of an N-element phased array with variable delay element is shown in Fig.1 where N identical antennas are uniformly spaced by a distance d along an axis. Fig. 1- Block diagram of N-element phased array Individual variable time delay elements are incorporated at each signal path before transmitting the signals to control the phases of the signals. At an angle of θ to the normal direction a plane-wave beam is assumed to be incident upon the antenna array. Due to the spacing between the antenna elements, the radiating element will experience a time delay [10], as written in Eqn.1, to reach the successive antennas. 2πd sin( θ ) τ = (1) λ Here, λ is the wavelength of the signals. However, signals received by each of the antennas can be written as Eqn. 2 after assuming incoming signal is a sinusoid at frequency ω with amplitude of A. Si=Ae jn τ (2) To compensate linear delay progression of the signal arrived at the successive phased array antenna elements due to the spacing between the elements, variable delay circuits must be introduce analogous but with reverse delay progression. In the uniform linear arrays, variable time delays are designed to allow uniform phase progression across the array. Hence, the output signal in each channel of the variable delay block can be written as Eqn. 3 S ' i = Ae jn τ e jnα (3) Where α stands for the difference in phase shift provided by two successive variable time delay elements. However, array factor [10] equal to the sum of all the signals normalized to the signal at one path can be written as Eqn. 4. F = N n= 1 e jn( τ α) According to Eqn.4, the peak of the array factor occurs at an incident angle which can be determined by Eqn. 5. 2πd sin( θ) = α (5) λ At this incident angle, which is known as scan angle, the linear delay progression introduced by the wave arriving at the successive antennas is accurately compensated with the time delay elements incorporated at each path. The array factor can also be shown as Eqn. 6. 2 N 2πd sin [ ( sin( θin) α)] F = 2 λ (6) 2 2πd sin [( sin( θin ) α)] 2λ The array factor has a maximum value of N 2 [10] at the scan angle θ. F will be lower than this value indicating spatial selectivity of phased array for other angles of incident. One of the key capabilities of PAA is that instead of using mechanical rotation of antenna array we can increase the peak gain of the array through exercising electronically tunable variable time delay elements. By increasing the number of phased array elements we can increase the efficiency of the phased array antenna. In addition, to enhance the spatial selectivity of phased array the beam width of the array can be reduced by enhancing the number of array elements. (4)
Fig.2. Uniform Linear Array III. UNIFROM LINEAR ARRAY We can make the structure of the linear phased array [11] [12] arranging the elements in a straight line in one dimension. These antennas within a straight line in one dimension are fed about a common phase shifter or time delay elements. Linear arrays are designed to produce a narrow beam width. Linear antenna arrays can have uniform or non-uniform spacing between elements. Commonly used linear antenna array is the Uniform Linear Array shown in Fig.2 where we have simulated ULA for 100 elements keeping element spacing 100mm with aperture size of 10m in Y-axis. For SSPS we need narrower main lobe at the center by suppressing the side lobes as far as possible. IV. RADIATION PATTERNS A common notation in the antenna literature is used here, where λ is wavelength, d is element spacing.now we will show how the radiation pattern changes as the parameters are modified. We have simulated all the radiation pattern by using MATLAB for the 100 elements phased array varying the ratio between the uniform distance of the phased array element and wavelength of the signal. For the ratio between the uniform distance of the phased array element and wavelength of the signal, d/ λ =0.05 we get the simulated beam pattern in Fig.3 with a wide main lobe with several side lobes. Fig.3 Radiation pattern when ratio between distance and wavelength d/λ=0.05
Fig.4 Radiation pattern when ratio between distance and wavelength d/ λ =0.3 After taking the ratio between the uniform distance of the phased array element and wavelength of the signal, d/λ =0.3 shown in Fig.4 we get narrower main lobe with some small side lobes. After increasing the ratio of d/λ from 0.05 to 0.3 main beam width seems to be narrower than the earlier one with minimizing and decreasing the height of the side lobes. Fig. 6 Radiation pattern when ratio between distance and wavelength d/ λ =3 lobes. For the higher efficiency from the phased array antenna for SPS system we need narrower beam width with reducing all of the side lobes. From Fig.5 we can say that normalized radiation pattern of main beam at the center is thin enough keeping the side lobes almost at zero level which is the best possible result for 100 elements phased array antennas for SPS system from the simulation result. Fig. 5 Radiation pattern when ratio between distance and wavelength d/ λ =0.8 When we switch to the ratio of d/λ from 0.3 to 0.8 we get our desire beam pattern by suppressing almost all of the side Fig. 7 Radiation pattern when ratio between distance and wavelength d/ λ =8 Moreover, we have simulated the radiation pattern for the phased array of 100 elements for d/λ =3 and d/λ =8 shown
in the Fig.6 and Fig.7 respectively where we can see that there are several side lobes having normalized radiation patterns much bigger than the main lobe. When we switch into the ratio of d/λ =8 shown in figure 7 we find normalized radiation patterns of main lobe is in the range of 0.21 where side lobes are between the ranges of 0.85 to 1 which is not acceptable. According to the above simulation result we can conclude that for the 100 element uniform linear phased array antenna, d/λ =0.8 is the best possible radiation pattern for SPS system. V. CONCLUSION In search for the alternative source of rapidly dwindling fossil fuel resources and for the replacement of the hazardous nuclear power plant Space based Solar Power Satellite system is a potential solution which will provide a consistent, stable and renewable source of energy for a long time once the initial investment is made. Phased array antenna is the significant part of the SSPS system for the highly efficient microwave power transfer. From our observation it is asserted that for the 100 elements phased array antenna if we can keep the ratio between uniform distance of the phased array element and wavelength of the signal in the range of 0.8 then we will get the desire radiation pattern of the main beam width keeping the side lobes almost in the zero level. However, if we can overcome the economical constraint to launch SSPS system as well as practical implementation of efficient phased array antenna SSPS system will minimize highly demandable power crisis for the developing country as well as for the world. Our obvious area of future improvement will be to investigate the highly radiation pattern of phased array increasing the total elements which may include further analysis of time delay elements. REFERENCES [1] Golap Kanti Dey, Kazi Tanvir Ahmmed; Multi-Junction Solar Cells and Microwave Power Transmission Technologies for Solar Power Satellite, 3rd IEEE International Conference on Informatics, Electronics & Vision, pp-1-6, 2014. [2]R. C. Hansen, Phased Array Antennas Second Edition, Copyright-2009 by John Wiley & Sons, Inc., 2009. [3] Hsi-Tseng Chou, Chien-Te Yu Design of phased array antennas with beam switching capability in the near-field focus applications IET Microwave Antennas Propagation., Vol. 9, Issue. 11, pp. 1120 1127, 2015. [4] Takenori Yasuzumi, et al. A Study on Phased Array Antenna Using MSA Composed by 3-patches, Loughborough Antennas & Propagation Conference UK, pp. 281-284. 2009. [5] Tuan Thanh Ta, et al. A 3-D Radiation Pattern Measurement Method for a 60-GHz-Band WPAN Phased Array Antenna, Proceedings of APMC 2012, Kaohsiung, Taiwan, pp. 139-141, 2012. [6] Takaki Ishikawa, Yuta Kubo, Junki Yoshino and Naoki Shinohara Study of Beam Forming for Microwave Power Transmission toward Solar Power Satellite with Advanced Phased Array System in Kyoto University, 2013 IEEE Antennas and Propagation Society International Symposium (APSURSI), 2225 2226, 2013. [7] Gregory M. Turner, Christos Christodoulou, FDTD Analysis of Phased Array Antennas, IEEE Transactions on Antennas and Propagation, Vol. 47, No. 4, 1999. [8] Hiroyuki Kayano, et al. Low-Profile High-Sensitivity Sub-array Module with HTS Filters for an Active Phased Array Antenna, IEEE Radar Conference, pp. 118-121, May 2014. [9] N. C. Karmakar, M. E. Bialkowski, Electronically Steerable Array Antennas for Mobile Satellite Communications-a review, Proceedings of the IEEE International Conference on Phased Array Systems and Technology, Dana Point, CA, USA, pp. 81 84, 2000. [10] D. Ehyaie, Novel approaches to the design of phased array antennas (Ph.D. thesis), University of Michigan, Ann Arbor, Mich, USA, 2011. [11] Matthew G. Bray, et al. Optimization of Thinned Aperiodic Linear Phased Arrays Using Genetic Algorithms to Reduce Grating Lobes During Scanning, IEEE Transactions on Antennas and Propagation, Vol. 50, No. 12, pp. 1732-1742, 2002. [12] Matthew G. Bray, et al. Thinned aperiodic linear phased array optimization for reduced grating lobes during scanning with input impedance bounds, IEEE Antennas and Propagation Society International Symposium, Boston, USA, Vol. 3, pp. 688-691,2001.