Design of a rectangular patch antenna


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Design of a rectangular patch antenna

  1. 1. ECM 521 TECHNICAL REPORT 2011 Design of a Rectangular Microstrip Patch Antenna cost. The selection of microstrip antenna technology can fulfill these requirements [3]. Abstract— Throughout this technical report, WLAN in the 2.4 GHz band(2.4-2.483 GHz) hasit will briefly describe the design of a made rapid progress and severalIEEE standardsrectangular patch antenna in free space as are available namely 802.11a, b, g and j[1].required aided with special software. The Various design techniques using defected groundsoftware used is Computer Simulation structure (DGS) in the patch antenna have beenTechnology 2011(CST). Based on an ordinary suggested in previous publications [2-4]. DGS ispatch antenna, the antenna has isolated realized by etching a defect in the ground plane oftriangle gaps and crossed strip-line gaps etched planar circuits and antennas. This defect disturbson the metal patch and ground plane, the shield current distribution in the ground planerespectively. Demonstrated to have left-handed and modifies a transmission line such as linecharacteristics, the patterned metal patch and capacitance and inductance characteristics [6].finite ground plane form a coupled capacitive- Accordingly, a DGS is able to provide a wideinductive circuit of negative index band-stop characteristic in some frequency bandsmetamaterial. It is shown to have great impact with a reduced number of unit cells. Due to theiron the antenna performance enhancement in excellent pass and rejection frequency bandterms of the bandwidth significantly broadened characteristics [6], DGS circuits are widely usedfrom a few hundred MHz to a few GHz, and in various active and passive microwave andalso in terms of high efficiency, low loss and millimeter-wave devices [7]. The purpose of thislow voltage standing wave ratio.Experimental work is to design and enhance a rectangulardata show a reasonably good agreement microstrip patch antenna using the parametersbetween the simulation and measured results. given.This antenna has strong radiation in thehorizontal direction for some specificalapplications within the entire band.Thesimulation and results that were going to be II. METHODOLOGYdiscussed in this report was based on theparameter value given as such that the A. Review Stagefrequency is 3(GHz) with the material type ofRT/Duroid 5870 while the value of permittivity To begin with, the dimensions of the rectangularis 2.33. Besides that the given value of substrate patch were calculated using formulae as beingthickness(mm) and copper thickness(mm) is shown below.The width is critical in terms of0.508 and 0.035 respectively. power efficiency, antenna impedance andbandwidth. It is largely dependent on the operating frequency and the substrate Keywords—Patch antenna, microstrip, CST, dielectricconstant. The equation (1) below waspermittivity, fringing effect, return loss used to work out the width of the patch. Other widthscould have been used but if it is too small then radiator efficiency will suffer and if it istoo I. INTRODUCTION large higher order modes will be excited, resulting in field distortions [1, pg-57]. icrostrip patch antenna antenna used to send onboard parameters of article to the groundMwhile under operating conditions. such asWireless local area networks (WLAN), mobileand sets require lightweight, small size and low 1
  2. 2. ECM 521 TECHNICAL REPORT 2011 To determine the extension of length, we use this formula: (3)Figure 1 –Front view of the patch (4)Figure 2 –Structure of the patch (1) The actual length, L of the patch is using the following formula: (5)The effective dielectric constant due to the airdielectric boundary is given by: (2) 2
  3. 3. ECM 521 TECHNICAL REPORT 2011 B. Final Stage as calculated previously was used to calculate the value of conductance as shown below; (7) (6)where (6-a) 0 0 sin 3 (8) Where using the asymptotic methods [5] that it can be shown as following ; So,The calculated is then being referred toAPPENDIX : Cosine and Sine Integrals [5]. To find the value of , we use equation below; (9)Therefore, solve for equation (6) ; (10) 3
  4. 4. ECM 521 TECHNICAL REPORT 2011Using the CST2011 software, is thencalculated, and the value obtained is 1.5218. III. RESULT AND DISCUSSIONThe software used to design and simulate the Figure 4 –the S-parameter diagrammicrostrip patch antenna can be used to calculate Based on the figure above, the S-and plot S11 parameters, VSWR, radiation pattern parameter is not achieved -10dB which is the idealand others. magnitude. The return loss for this figure is : The figures below were the results on 20 log10 S11 = -2.6designing the microstrip patch antenna with thegiven specifications. S11 = 0.7413 Figure 5 –Farfield pattern of the patchFigure 3 –Top view of the designated patch The patch’s radiation at the fringing fieldScattering parameter ( S- Parameter ) is used to results in a certain far-field radiation patterns. Themodel N-Port linear electrical networks. For N = figure above shows that the antenna radiates more1, S-Matrix is [S11] consists of single element. [S11 power in the red area (z-axis) than another] parameter also known as Reflection Coefficient. direction. The directivity of this antenna isIt is a complex number that has magnitude and 7.057dBi.The IEEE standard is for an antenna tophase angle. When magnitude of S11 is expressed have a -10dB S-parameter magnitude. Thein decibels, is known as return loss at the input scattering parameter shown above shows that theand it always in decibels. It can be expressed by: curve falls at a frequency of 2.98GHz which isRLinput = 20 log10 |S11| dB near enough to 3GHz as given in the specification. The nearest to its frequency, the better the performance as it has a sharper curve and a lower S-parameter magnitude in dB. A lower dB indicates the antenna having a greater directivity 4
  5. 5. ECM 521 TECHNICAL REPORT 2011and gain.A DGS unit cell is a defect in the ground Now, the S-Parameter achieved -10dB as theplane of a physical transmission line be it minimum ideal of parameter. By formula of returnmicrostrip, coplanar waveguide or whatever loss shows before, the return loss is calculated as:structure where a reference ground planeconductor exists, which is capable of producing a 20log S11 = -10.98dBtransmission zero in the response of the structure. S11 = 0.282The resonant frequency of this transmission zerodepends on the physical dimensions of the defect. As we compared the value of the return lossThe main advantage of DGS, that it is easier to before and after done the DGS, the return lossmodel and therefore to use in more complex after is less than before doing the DGS. Thestructures. The first DGS structure is the well- smaller the value of the return loss, the smaller theknown dumbbell shaped DGS, published in 1998 reflected power due to we want the maximum[8]. The use of a DGS (slot in the ground plane) power transferred. So when there are less loss inallows the apparition of a stop band controlled by the antenna, it will achieve best performance oftuning the dimensions of the slot. The ground radiation and high gain as well.plate which has a strong E-Field is cut away inorder to get the better bandwidth. Figure 9 –Farfield pattern after DGS IV. CONCLUSIONFigure 7 –E-field resulted after DGS From the analysis as above, it can be concluded that the greater substrate thickness will get a greater gain and directivity. The results demonstrated that the radiation properties of the antenna with DGS is better performance than the antenna without DGS as the S-parameter is measured to below than -10dB. It is also shown that DGS have an effectto the performance of the antenna characteristics.As the dielectric constant of the substrate increase, the antenna bandwidth decrease and therefore decrease the impedance bandwidth.Figure 8 –The S-parameter after DGS 5
  6. 6. ECM 521 TECHNICAL REPORT 2011 V. RECOMMENDATIONS Suppression For Microstrip Patch Antennas”, Microwave and Optical Technology Letters, pp. Microstrip patch antennas radiate primarily 103-105 Vol. 49, No. 1, January 2007.because of the fringing fields between the patchedge and the ground plane. For a good [3] Haiwen Liu, Zhengfan Li, Xiaowei Sun, andperformance of antenna, a thick dielectric Junfa, “Harmonic Suppression With Photonicsubstrate having a low dielectric constant is Bandgap and Defected Ground Structure for anecessary since it provides larger bandwidth, Microstrip Patch Antenna”, IEEE Microwave andbetter radiation and better efficiency. However, it Wireless Components Letters, VOL. 15, NO. 2,leads to a larger antenna size. In order to reducethe size of the Microstrip patch antenna, substrates Feb. 2005.with higher dielectric constants must be used [4] Y. J. Sung, M. Kim, and Y.-S. Kim,which are less efficient and result in narrowbandwidth. Hence a trade-off must be realized “Harmonics Reduction With Defected Groundbetween the antenna performance and antenna Structure for a Microstrip Patch Antenna”, IEEEdimensions Antennas and Wireless Propagation Letters, VOL. 2, 2003. [5] Constantine A. Balanis, “Antenna Theory Analysis And Design”, 3rdedition , page 811-842 VI. ACKNOWLEDGMENT [6] D. Ahn, J. S. Park, C. S. Kim, J. Kim, Y. Qian, In the name of Allah s.w.t and He most and T. Itoh, “A design of the low-pass filter using merciful with Salawat and salam to prophet Muhammad s.a.w, Alhamdulillah thanks to Him the novel microstrip defected ground structure,” with the help and His permission giving us the IEEE Trans. Microwave Theory Tech., vol. 49, idea and health, also the opportunity to pp. 86–93, Jan. 2001. successfully completed this project entitled “Design of A Rectangular Patch Antenna Using [7] C. S. Kim, J. S. Park, D. Ahn, and J. B. Lim, CST”for Computer Engineering System Design “A novel 1-D periodic defected ground structure subject within the given time duration. for planar circuits,” IEEE Microwave Guided Wave Lett., vol. 10, pp. 131–133, Apr.2000. Here, we would to express our great thankful wishes to all of those who have been [8] J. I. Park, C. S. Kim, J. Kim, J. S. Park, Y. very supporting and helpful to us especially our Antenna and Propagation lecturer, Pn.Nor Qian, D. Ahn, and T. Itoh,―Modeling of a Hasimah Baba for her guidance, advices,and photonic bandgap and its application for the low- monitoring us to complete this project. Special pass filter design,‖ Proceedings of Asia Pacific thanks also to all classmates of EE2405A and Microw. Conf. (APMC), pp. 331–334, Singapore other friends who are involved directly or 1999. indirectly to accomplish this task. The full and kindness of support, attention, time and advises gives a full memories to me. VII. REFERENCES[1] Bahl, I. J and Bhartia, P; “MicrostripAntennas”, Artech House, 1980.[2] M. K. Mandal, P. Mondal, S. Sanyal, and A.Chakrabarty , “An Improved Design Of Harmonic 6