ANALYSIS OF LINEARLY AND CIRCULARLY POLARIZED MICROSTRIP PATCH ANTENNA ARRAY 1 RANJANI M.N, 2 B. SIVAKUMAR 1 Asst. Prof, Department of Telecommunication Engineering, Dr. AIT, Bangalore 2 Professor & HOD, Department of Telecommunication Engineering, Dr. AIT, Bangalore E-mail: 1 ranjanimanur@gmail.com, 2 sivabs2000@yahoo.co.uk Abstract- Characteristics of patch antennas like beam scanning, high gain, or steering capability are possible only when discrete patch elements are combined to form arrays. The elements of an array may be spatially distributed to form a linear, planar, or volume array. Conventional antennas and microstrip antennas are crucial for application in modern communication and navigation systems. Microstrip antennas can conform to planar and non-planar surfaces. Hence they find wide usage in military and civilian applications like aerospace structures where weight and space are a restriction. The design of a four-element circularly polarized and linearly polarized microstrip antenna array, which is based on Uniform and Binomial power distribution, using FEKO is presented in this paper. Keywords- microstrip patch array, linear polarization, circular polarization, binomial distribution, pin fed I. INTRODUCTION While choosing and installing of an antenna the Antenna Polarization is an important parameter. Majority of the communication systems use horizontal, vertical or circular polarization. Hence it is very important for the antenna user to know the difference between polarizations and how to maximize their benefit. Linearly polarized antenna radiates in the plane containing the direction of propagation. A circularly polarized antenna rotates one complete revolution during one period of the wave, while vertical polarized antenna will have electric field perpendicular to the earth s surface. The axial ratio is the ratio of orthogonal components of an E-field. The axial ratio of a linearly polarized antenna will be infinite as the orthogonal components of the electric field are zero, while, for a circularly polarized antenna the electric field components are made of two components equal in amplitude and 90 degrees out of phase. Therefore the axial ratio is 1 (or 0dB). ε reff = + 1 + 12 h = 1.97 (2) The effective length of the patch is given by the equation, (3) L eff = ε = 10.664 mm (3) ΔL = 0.412 h (.) ( h.) (.) ( = 0.768mm h.) (4) The length of the patch is given by (5) L= L eff - 2 ΔL =9.128mm (5) The feed offset is calculated to be x0 = 1.369 mm. The single element patch is first constructed as shown in Fig (1). II. DESIGN OF 1X4 RECTANGULAR MICROSTRIP ANTENNA ARRAY 2.1. Construction of a single patch The microstrip patch antenna is constructed and simulated using FEKO 7.0 with the following design parameters. The frequency f r = 10 GHz, ε r = 2.2, tanδ = 0.005, substrate height sub_ht = 1.5mm, the thickness of the metal is 0.016mm, the width and length of the patch is calculated using the following equations. The width of the patch is calculated using the equation (1) W= = 11.85 mm (1) The effective relative permittivity of the substrate ε reff is calculated using the equation (2) Fig 1 : Single element patch 2.2. Construction of 1X4 patch antenna array A linear array is created by adding 4 elements along the x axis and element spacing is λ/2. The resulting array is as shown in Fig (2). 33
same for all sources. Linear polarization is measured. The array is dual fed to obtain circular polarization. III. RESULTS AND DISCUSSION 3.1. The Radiation Pattern The 3-D radiation pattern of the uniformly distributed rectangular patch antenna array is shown in Fig (4). Fig 2: The 4 element patch antenna array While creating the linear array, the uniform distribution is chosen, thereby each element of the array is fed by sources with same magnitude and phase. Using this model, the linear polarization of the array is measured and radiation pattern is observed. In an antenna, circular polarization can be achieved through a single feed or using two feeds in the same patch. In an antenna array, we can generate circular polarization by the sequential rotation of the feeders. The most common and direct way to generate a circular polarization is through the use of a dual-feed technique. The two orthogonal modes required for the generation of circular polarization can be simultaneously excited using two feeds at orthogonal positions that are fed by 1 0 0 and 1 90 0. The construction remaining the same, the array is excited by dual fed method, for circular polarization. This is as shown in Fig (3). Fig 4: 3-D radiation pattern of uniformly distributed linearly polarized rectangular patch antenna array The 3-D radiation pattern of uniformly distributed circularly polarized array is shown if Fig (5).The Circular polarization increases the gain of the array. Fig 5: 3-D radiation pattern of uniformly distributed circularly polarized rectangular patch antenna array 3.2. The plot of Gain Fig 3: Dual Fed Circularly Polarized microstrip patch antenna array The circular polarization axial ratio is measured. The same array is modified to obtain the binomial distribution array, by feeding each element of the array with the binomial coefficients, here we have chosen (0.333, 1, 1, 0.333). The phase remains the Fig 6: Variation of Gain and Theta of linear and circular polarization antenna array 34
Fig 7: Polar plot of linearly and circularly polarized uniformly distributed linear patch antenna array. The axial ratio is represented in 3D as shown in the Fig (8). Fig 10: 3D radiation pattern for binomial distribution & linear polarization of rectangular patch array The 3D radiation pattern for binomial distribution & circular polarization of rectangular patch array is shown in Fig (11) Fig 8: The linear polarization 3D view of uniformly distributed linear rectangular patch antenna array Fig 11: 3D radiation pattern for binomial distribution & linear polarization of rectangular patch array The variation of theta and Gain of the antenna array is plotted, Fig (12). Fig 9: The Circular polarization 3D view of uniformly distributed linear rectangular patch antenna array The 3D radiation pattern for binomial distribution & linear polarization of rectangular patch array is shown in Fig (10) Fig 12: The variation of theta and Gain of the antenna array for linear and circular polarization. 35
The gain and sidelobe levels measured are tabulated in table (1). Table 1: The Gain, SLL & HPBW for uniform and Binomial Distribution for Linear and Circular Polarization Fig 13: Polar plot of linearly and circularly polarized binomial distributed linear patch antenna array The axial ratio is represented in 3D as shown in the Fig (14). Fig 14: The linear polarization 3D view of binomial distributed linear rectangular patch antenna array From table (1) it is observed that the Gain of the binomial distribution with linear and binomial distribution decreases but the Gain due to circular polarization increases when compared to linear polarization. The table (2) gives the power radiated due to circular and linear polarization for uniform and binomial distribution. Table 2: Polarization Dependent radiated power Fig 15: The Circular polarization 3D view of binomial distributed linear rectangular patch antenna array CONCLUSIONS A thorough analysis of the effect of linear and circular polarization is presented in the paper. 36
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