HIGH GAIN MICROSTRIP PATCH ANTENNA USING FSS FOR 2.45 GHZ RFID APPLICATIONS

Transcription

1 HIGH GAIN MICROSTRIP PATCH ANTENNA USING FSS FOR 2.45 GHZ RFID APPLICATIONS PROJECT REFERENCE NO.: 39S_BE_0791 COLLEGE : KLE DR. M. SHESHGIRI COLLEGE OF ENGINEERING AND TECHNOLOGY, BELAGAVI BRANCH : DEPARTMENT OF ELECTRONICS AND COMMUNICATIONS ENGINEERING GUIE : PROF. ARUN TIGADI STUDENTS : MR. AZILDA RODRIGUES MS. NEHA HIREMATH MR. FAYAZAHMED ATTAR MR. SANDEEP MISHRA KEYWORDS: Microstrip antenna, FSS, ISM Band, Co-axial feed, Impedence matching, Directivity, Return loss. INTRODUCTION: In recent years, radio frequency identification technology has moved from obscurity into mainstream applications that help speed the handling of manufactured goods and materials. RFID (Radio Frequency Identification) enables identification from a distance, and unlike earlier barcode technology, it does so without requiring a line of sight. The RFID system consists of three basic components: a transponder, a reader and host data processing system. In our project we have implemented an antenna that is used to detect the object i.ethrough the transponder, we have used a center frequency of 2.45GHz with FSS Structures (Frequency Selective Surfaces) in order to increase the bandwidth and the gain which will provide larger coverage at a lower cost. This antenna when implemented into the RFID system will provide the same function but with lesser cost. The already implemented RFID system antenna are different from the fact that we made use of FSS structures in order to increase the bandwidth and the gain.a frequency selective surface is a periodic array of either radiating or non-radiating elements or slots which effectively act as a band stop or band pass filter respectively to electromagnetic waves. OBJECTIVES: The objective of the project is to increase the gain of the rectangular patch antenna for RFID application(2.45ghz). The simulation was performed using the Ansoft HFSS v13.0

2 METHODOLOGY: Fig 1: Structure of a rectangular microstrip patch antenna. Table 1: Dimensions for the antenna geometry shown in Fig 7.2. Parameter Value Length of the radiator Patch (L) 29.0mm Width of the radiator Patch (W) 38.5mm Effective dielectric constant(ε r ) 2.2 Height of radiator patch (H) 0.1mm Height of the dielectric substrate(sh) 3.2mm Length of the dielectric substrate (SL) 90.0mm Width of the dielectric substrate (SW) 100.0mm The three essential parameters for the design of a rectangular Microstrip Patch Antenna are: Frequency of operation (f 0 ): The resonant frequency of the antenna must be selected appropriately. Uses the frequency 2.45GHz. Hence the antenna designed must be able to operate in this frequency range. The resonant center frequency selected for our design is 2.45GHz. Dielectric constant of the substrate (ε r ): The dielectric material selected for our design is duriod 5880 which has a dielectric constant of 2.2 with tan δ= Height of dielectric substrate (h): The height of the dielectric substrate is selected as 3.2mm. The following formulas are used to design the simple microstrip patch antenna. Step 1: Calculation of the Width (W): The width of the Microstrip patch antenna is given by equation (4.2) as: where; C - Free space velocity of light, 3 x 10 8 m/s, f 0 - Frequency of operation, ε r - Dielectric constant (4.2)

3 Step 2: Calculation of Effective dielectric constant (ε reff ):Equation (4.3) gives the effective dielectric constant as: (4.3) where, ε r -Dielectric constant, h- Height of dielectric substrate, W -Width of the patch Step 3: Calculation of the Effective length (L eff ): Equation (4.4) gives the effective length as: where; (4.4) C - Free space velocity of light, 3 x 10 8 m/s, f 0 - Frequency of operation ε reff - Effective dielectric constant Step 4: Calculation of the length extension (ΔL):Equation (4.5) gives the length extension as: Step 5: Calculation of actual length of patch (L):The actual length is obtained by re-writing equation (4.6) as: (4.6) Step 6: Determination of feed point location (X f,y f ): A coaxial probe type feed is used in our design as shown in fig 4.6. As shown in Figure 4.5, the center of the patch is taken as the origin and the feed point location is given by the co-ordinates (X f, Yf) from the origin. The feed point must be located at that point on the patch, where the input impedance is 50 ohms for the resonant frequency. Hence, a trial and error method is used to locate the feed point. For different locations of the feed point, the return loss (R.L) is compared and that feed point is selected where the R.L is most negative. There exists a point along the length of the patch where the R.L is minimum. (4.5)

4 Fig 2: Top view of Microstrip Patch Antenna. RESULTS AND CONCLUSIONS: Antenna Geometry and Its Optimization Fig 3: Side view of Microstrip Patch Antenna. The design of the proposed antenna involve two phases, the first phase is to design and simulate a simple micro strip patch antenna and the second phase involves design and simulation of patch antenna with FSS structures using the design in the first phase as a base antenna. Fig 4: Basic Geometry of a simple rectangular micro strip patch antenna. FSS Structure Design To design the FSS structure, there is no specific formula created to calculate the size of the FSS structure to get the band gap characteristic at certain operational frequency, the parametric study will be used. Fig 5.2 shows the geometry of a microstrip patch antenna

5 surrounded by a FSS structure. The modelled antenna shown in Fig 5.2 is simulated using Ansoft HFSS for gain, return loss and VSWR. The 3D FSS structure antenna is designed on Duriod 5880 dielectric with 10x5 arrays of square patches beside the rectangular patch of planar antenna on the same plane. Fig 5: Geometry of mushroom-like FSS Patch antenna. Optimization Strategy A simple algorithmic iterative strategy is used to optimize the physical dimensions of the antenna to maximize the gain by retaining the operating frequency at 2.45GHz and voltage standing wave ratio (VSWR) 2. The dimension of the FSS structures was fixed at 10mmx5mm. Distance between patches g in both length and width directions were initially varied noting the changes in Frequency and Gain of antenna for a number of iterations. In order to obtain the designed operating frequency, initially distance along the length of FSS structures was varied (increased) from 0.2mm by retaining VSWR below the value two. Once the operating frequency is attained, then gap g between the patches (distance along Width) is increased to maximize the gain of the FSS structure. A number of iterations led to designed frequency and these values were fixed. SCOPE FOR FUTURE WORK: There are number of planar antennas available in literature which addresses key problems like low gain, directivity and back lobe radiation due to surface waves. But, in proposed design, a high gain patch antenna with FSS antenna is presented having high gain, high directivity and good radiation patterns from a single coaxial fed. Hence, with slight modification in the design, benefits can be accomplished. Some of the future areas of work are: By varying the shape of the antenna, it is possible to obtain antenna with dual band of operation. A wideband microstrip patch antenna can be obtained from narrow band antenna by introducing rectangular slots properly positioned along the diagonal of the square patch antenna. By introducing FSS structures in between Microstrip patch array antenna, it is possible to reduce the mutual coupling between the patch arrays.