e-issn 2455 1392 Volume 2 Issue 4, April 2016 pp. 636-643 Scientific Journal Impact Factor : 3.468 http://www.ijcter.com Analysis and Comparative Study of Microstrip Patch Antenna on Different Substrate Materials Akash Mithari 1, Uday Patil 2 1 Student, 2 Assistant Professor Department of Electronics Technology Engg., Shivaji University, Kolhapur, Maharashtra, India Abstract This paper discusses the performance of various dielectric substrates, having dielectric constants ranging from 2 to 5.. These designs are basically rectangular micro strip patch antennas for wireless communication resonating at 2.4 GHz. Substrate is used for this purpose is FR4 glass epoxy, RT Duroid, Rogers, Teflon with dielectric constant of 4.4, 3.2, 2.2 respectively. Keeping the thickness of substrate fixed to 1.6mm. The shape used for conventional patch antenna is rectangular with insert feed. Comparison is based on Return loss, Bandwidth, Radiation pattern, VSWR characteristics, Efficiency, Simulated 3-D radiation pattern, Gain, Directivity. Analysis of each is done and compiled using High Frequency Structured Simulator (HFSS). Keywords Microstrip Rectangular Patch Antenna (MRPA), Flame Retardant 4 (FR4), Rogers, RT/Duroid I. INTRODUCTION The Substrates used in microstrip antenna primarily provides mechanical strength to the antenna. The dielectric medium allows surface waves to propagate through it, which will extract some part of total power available for radiation. It degrades the electrical properties of antenna. The cost of antenna design is also affected by dielectric material, hence it require intelligent decision while selecting substrate so as to satisfy both electrical and mechanical requirement for the antenna. Generally a dielectric substrate is defined by its two prime parameters one is its permittivity (It describes the materials with high polarizability) and another is loss tangent (It explains the dissipation of electromagnetic energy). A dielectric substrate is a insulator which is a main constituent of the microstrip structure. A thickness of substrate has direct proportionality with bandwidth. Dielectric constant is inversely proportional to bandwidth. As lower the relative permittivity better the fringing is achieved [1]. Another factor that impact directly is loss tangent it shows inverse relation with efficiency and substrate with lower loss tangent is costlier. Permittivity of substrate is critical parameter in controlling band width, efficiency, and radiation pattern of patch antenna. However, higher dielectric constant also reduces bandwidth and radiation efficiency. Dielectrics are used in capacitors to store more electric charge than vacuum. Lower the dielectric constant better the material works as insulator and because of this, better it resist electrons to be absorbed in the dielectric material, creating less loss. There are numerous substrates that can be used for the design of MPAs and their dielectric constants are usually in the range of 2.2 εr 12. MPAs radiate primarily because of the fringing fields between the patch edge and the ground plane. The dielectric constant is the ratio between the stored amount of electrical energy in a material and to that stored by a vacuum. It is also a measure of the degree to which an electromagnetic wave is slowed down as it travels through the insulating material. Dielectric constants for some everyday materials are listed in table 1. In present paper rectangular micro strip antenna with insert feed is analyzed, thickness and resonant frequency is kept constant. Performance evaluation of each substrate is showed by changing dielectric constant. The characteristics for substrates available in markets are listed in table 2. @IJCTER-2016, All rights Reserved 636
Table 1. Dielectric Constant of some important quantities Material Dielectric Constant Vacuum 1.0 Air 1.0006 Rubber 2.1 Glass 7.8 Water (32 deg F) 88 Table 2. Characteristics of Selected Substrate Materials Parameters Bakelite FR4 Glass Epoxy RT Duroid Rogers 4003 Dielectric Constant 4.78 4.2-5.2 2.2 3.4 Loss Tangent 0.030 0.013-0.030 04 2 Water Absorption 0.5-1.3% <0.25% 0.02% 0.06% Tensile Strength 60 MPa <310MPa 450MPa 141MPa Volume Resistivity Mohm cm Mohm cm Mohm cm Mohm cm Surface Resistivity Mohm Mohm Mohm Mohm Breakdown Voltage 20-28kV 55kV >60kV - Density 1810kg/ 1850kg/ 2200kg/ 1790kg/ II. FEEDING TECHNIQUES There are many feeding techniques namely Microstrip Feed, Co-axial Feed, quarter wavelength feed etc. The simplest method of feeding the patch is by a coplanar microstrip line, photo etched on the substrate. So this insert feeding is used for performance evaluation as shown in figure 1. At the edge of the radiating voltage distribution is high and current is low so patch impedance is very high at the edge. This method is used to tune input impedance to the desired value. The current is low at the end of the half-wave, as Feed inserted towards the center current increases. Due to this voltage decreases Zo = V/I input impedance is reduced when insert feed towards center. @IJCTER-2016, All rights Reserved 637
Figure 1. Geometry for Rectangular Microstrip Patch antenna with insert Feed III. DESIGN CONSIDERATIONS Figure 1 shows the geometry of the proposed Rectangular Microstrip Antenna (RMPA). This antenna is designed on different substrates namely glass epoxy FR4 dielectric material with relative permittivity (εr) of 4.4, RT Duroid with(εr) of 3.2, Rogers (εr) of 2.2 and with thickness (h) of 1.6mm is chosen. The conventional MSA is designed for 2.4GHz with dimensions Ls and Ws radiating patch, which is excited by simple 50 Ω microstrip feed having dimensions length lp and width Wp for their impedance matching. The width of the patch antenna is calculated by formula [3], ( ) (1) Where C Velocity of light in air = 3 F Frequency of antenna = 2.4 - Dielectric constant of substrate m/s. Hz. Effective dielectric constant as given by Hammersted and Jensen [3], * + (2) Due to effect of fringing fields the length (L) increases by by length extension ( ) from physical length, which is given ( )( ) ( )( ) (3) Effective length of the patch = (4) @IJCTER-2016, All rights Reserved 638
Actual length of the patch: Ground plane calculations: International Journal of Current Trends in Engineering & Research (IJCTER) 6h+Width of the patch (6) 6h+Length of the patch (7) The dimensions of conventional patch antenna obtained using the above equations are listed in Table 1. Table 3. Parameters of Patch Antenna on different substrates Input parameter FR4 Rogers RT Duroid Width of patch 41 mm 49mm 48 mm Effective dielectric constant 4.2 3.2 2.2 Tangent loss 0.02 18 09 Length of patch 29 mm 33.69mm 41mm Insert feed point distance (y 0 ) 7mm 10 mm 12 mm Width of the strip line ( W o ) 3 mm 4.3 mm 4 mm Substrate length and width (WxL) 40mmx50mm 45 mm x 56 mm 56mm x 60mm (5) IV. RESULTS The observed results such as return loss, gain, radiation pattern, vswr and efficiency are discussed below, 1. Return Loss: 2.4000-26.1254 XY Plot 1 1 with fr4 2.4000-24.3915 XY Plot 1 2 with RtDuroid1 m2 2.3700-10.1405 m3 2.4344-10.0198 m2 2.3825-9.9991 m3 2.4223 88-5.00-5.00 m2 m3 m2m3-15.00-15.00-2 -25.00-2 -3 2.4100-24.7875 XY Plot 1-25.00 3 with rogers -5.00-15.00-2 -25.00 Figure 2. Reflection Coefficient of FR4 substrate (L= 40mm, W= 50mm, h=1.6mm, ɛ=4.4) Reflection Coefficient of RT Duroid substrate (L= 56mm, W= 60mm, h=1.6mm, ɛ=2.2) Reflection Coefficient of Rogers substrate (L= 56mm, W= 45mm, h=1.6mm, ɛ=3.4) @IJCTER-2016, All rights Reserved 639
International Journal of Current Trends in Engineering & Research (IJCTER) The figure 2 shows the return loss for the three different substrates. Figure 2 indicates the return loss for FR4 gives RL about -26 db, the RL of the RT Duroid is approximately -24.39 db shown in figure 2. Figure 2 shows the RL for Rogers substrate is around -24 db. As the observation while designing the antenna, while reducing the length and width of the patch antenna resonant frequency is increased. Bandwidth is also observed the FR4 have the BW of 10MHz, while Rogers and RT Duroid having the bandwidth of 12 MHz & 11 MHz respectively. 2. Gain: 4.00 00 2.9828 2.00 - XY Plot 3 1 with fr4 Freq='2.4GHz' Phi='0deg' Freq='2.4GHz' Phi='90deg' 1 00 7.4474 5.00 XY Plot 3 2 with RtDuroid1 Freq='2.4GHz' Phi='0deg' Freq='2.4GHz' Phi='90deg' -2.00-5.00-4.00-6.00-8.00-15.00-20 -15-10 -5 5 10 15 20 Theta [deg] 8.00 00 6.5781 6.00 4.00-2 -20-15 -10-5 5 10 15 20 Theta [deg] XY Plot 3 3 with rogers Freq='2.4GHz' Phi='0deg' Freq='2.4GHz' Phi='90deg' 2.00-2.00-4.00-6.00 Figure3. : Gain for FR4 substrate ɛ= 4.4 : Gain for RT Duroid substrate ɛ=2.2 : Gain for Rogers s substrate ɛ=3.4 Figure 3 a, b, c shows the gain for the three substrates. In which the FR4 have low gain of 2.98 db, while RT Duroid and Rogers have the gain of 7.44 db and 6.57 db respectively. The reason for increase in gain is due to the increase in size of the RT Duroid based antenna geometry compared to the other substrate based geometry as bandwidth is directly proportional to antenna dimensions or antenna size. Also, RT Duroid has lowest dielectric constant among the three substrates. 3. Radiation Pattern: -8.00-20 -15-10 -5 5 10 15 20 Theta [deg] @IJCTER-2016, All rights Reserved 640
Figure 4. : Radiation Pattern for FR4 substrate, : Radiation Pattern for RT Duroid substrate, : Radiation Pattern for Rogers substrate Above figure shows 2D radiation patterns for all three substrates. All substrates shows unipolar radiation pattern with small amount of back lobe shown. Figure 5 shows 3D radiation pattern with power transferred scale. In that maximum amount of the radiation occurs is in major lobe (with red portion). Figure 5. 3 D Radiation Pattern for FR4, RT Duroid, Rogers @IJCTER-2016, All rights Reserved 641
International Journal of Current Trends in Engineering & Research (IJCTER) 4. VSWR: 15 2.4000 1.1039 XY Plot 2 1 with fr4 125 2.4000 1.1284 XY Plot 2 2 with RtDuroid1 125.00 100 10 75 75.00 50 5 25.00 25 120 2.4000 1.3286 XY Plot 2 3 with rogers 100 80 60 40 20 Figure 6. VSWR Characteristics FR4, RT Duroid, Rogers As ideal value for the VSWR is 1 and typically measured in the ratio of 1:2. Figure 6 shows the VSWR for the different substrates antenna. As we get all the frequencies below -10dB that have VSWR in between 1:2. For FR4 VSWR is 1.1 and for RT Duroid & Rogers standing ratio is 1.12, 1.3 respectively. Table 3. Comparison of Results based on Results Parameters FR4 Glass Epoxy RT Duroid Rogers 4003 Antenna Dimensions (in mm) 40x50x1.6 56x60x1.6 45.x56x1.6 Patch Length and Width (in mm) 29x41 41x58 33.69x49 Resonant Frequency 2.4GHz 2.4GHz 2.4GHz Return Loss (in db) -26-24.39-24 Gain in (in dbi) 2.98 7.44 6.57 Bandwidth 10MHz 11MHz 12MHz VSWR 1:1.1 1:1.12 1:1.32 Directivity in (in dbi) 6.19 7.50 6.7 Efficiency 47.74% 96% 95.52% V. CONCLUSION The resonant frequency is 2.4 GHz and impedance is Z= 50 ohm for all the antennas. Amongst three antennas are analyzed with these conditions. In that RT Duroid gives return loss which is - 24.39dB, higher gain of 7.44dB, directivity of 7.5 db and better efficiency of 96% than other substrates. While FR4 gives efficiency which is only 47%. On the other hand size of the RT Duroid increases slightly. However all the antennas show lower bandwidth which is drawback of the microstrip antenna. @IJCTER-2016, All rights Reserved 642
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