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(IJCSIS) International Journal of Computer Science and Information Security, Vol. 10, No. 3, March 2012 Step Tapered waveguide with cylindrical waveguide Harshukumar Khare, Prof. R.D. Patane M.E (EXTC) Final year student Asst. Proffessor (EXTC) TEC, Nerul, Navi-Mumbai TEC, Nerul, Navi-Mumbai email@example.com firstname.lastname@example.org Abstract: Tapered Waveguide is a waveguide in which a the other standard values associated with circular waveguide physical or electrical characteristic changes continuously with can be done relatively easily. distance along the axis of the waveguide. Tapered waveguide A waveguide taper can always be built to have as low a offer an excellent means of converting microwave mode sizes to mode conversion as is wanted in a certain frequency band connect Microwave devices of different cross-sectional merely by making it long enough. However, an optimally dimensions. This paper discusses the waveguide component for designed taper has the smallest possible length for a given interconnecting rectangular and circular waveguide using step difference in diameters at its two ends for a specified tapering. Model is designed for the frequency range from 2 to 4 unwanted mode level in a given frequency band. Tapered GHz. Dominant Mode conversions ie from TE10 to TM11 is waveguide for matching impedance is nothing but a tapered considered for tapering techniques. Step tapering is studied at waveguide in which only one mode is propagating. Power different step sizes 4mm to 10 mm and analysis is done. All can only be converted into reflected waves, and it is this simulations done with CST Microwave studio and S reflected power which is kept small in a properly designed transmission line taper. If more than one mode is parameters and E field parameters are analyzed. Simulation propagating, power will be scattered not only into the result shows that wave is properly propagated with no power reflected wave but also into the other propagating modes. In reflection and low power loss. fact , the power scattered into backward traveling waves is Key words: Single & Double Step Tapering, Cylindrical quite small compared to the power scattered into forward waveguide, CST, S parameter, E Field traveling waves, and only the latter need be considered in a multimode waveguide taper. Therefore, the mode conversion in the waveguide transition corresponds to the I. INTRODUCTION reflection in transmission line taper. A rectangular waveguide supports TM and TE modes A waveguide mode is a unique arrangement of the but not TEM waves. A rectangular waveguide cannot electric and magnetic fields propagating in the z-direction propagate below some certain frequency. This frequency is that satisfies all Maxwell equations and boundary conditions called the cut-off frequency. imposed by the geometry of the conductors of the Circular waveguides offer implementation advantages transmission system. Various waveguide modes are TEM, over rectangular waveguide in that installation is much TE, TM and Hybrid modes. Dominant mode in Rectangular simpler when forming runs for turns and offsets - waveguide is TE10 and in circular waveguide TE11. To particularly when large radii are involved and the wind convert dominant mode in rectangular waveguide to loading is less on a round cross-section, meaning towers do dominant mode in circular waveguide tapered waveguide is not need to be as robust. Manufacturing is generally simpler, used. There are different types of tapering such as step too, since only one dimension the radius needs to be tapering, conical tapering elliptical tapering, etc. Analysis maintained. Applications where differential rotation is has been done using Step tapering with CST Microwave required, like a rotary joint for a radar antenna, absolutely Studio. require a circular cross-section, so even if rectangular waveguide is used for the primary routing, a transition to II. DESIGN ASPECT circular and then possibly back to rectangular is needed. The simulation was done by Transient solver of CST Calculations for circular waveguide require the application Microwave Studio. The Cartesian coordinate system (x, y, of Bessel functions, so working equations with a cheap and z) is used to model the 3D structure. Design & analysis calculator is not going to happen. However, even spreadsheets have Bessel function capability nowadays, so has been done with tapering and without tapering. determining cutoff frequencies, field strengths, and any of 64 http://sites.google.com/site/ijcsis/ ISSN 1947-5500 (IJCSIS) International Journal of Computer Science and Information Security, Vol. 10, No. 3, March 2012 A. Design without tapering The rectangular brick is directly connected to circular waveguide. Port of rectangular brick (Port 2) is excited and the S parameters are obtained by Transient Solver. 3D model of cylindrical waveguide and Rectangular Brick Without tapering is shown in fig 1. Fig 4 - 3D model of cylindrical waveguide and Rectangular Brick with Step tapering Simulated results for S parameters & E field are calculated for different step sizes for sizes of 4 mm & 10mm their S11 and S21 are shown in Fig 5. It is seen from Fig 5 that for step size 4 mm plots the sufficient amount of power is reflected back which shows that taper is not properly coupled and for step size 10 mm it is seen that no power is reflected back hence source is safe Fig 1 - 3D model of cylindrical waveguide and in this case. Rectangular Brick Without tapering S11 plot gives that around 2.1 GHz S11 goes upto 19 Step size 4mm Step Size 10mm dBas shown in Fig 2 which is not a desirable case as huge S11 S11 amount of power is reflected back to the source damaging the network analyzer. S21 S21 Fig 2 - S11 plot S21 plot is shown in fig. 3 which indicates that no sufficient output is coupled to the output port as it is approaching to 0dB i.e. no power is coupled from port 1 to port 2 and vice versa. Fig-5– S11 & S21 for Step size 4mm & 10 mm E Field distribution in single step tapered and cylindrical waveguide is shown in Fig. 6. Fig 3 - S21 plot B. Design with tapering i) Single Step tapering The 3D model of single step tapering is shown in Fig 4. Fig-6 E Field distribution in single step tapering 65 http://sites.google.com/site/ijcsis/ ISSN 1947-5500 (IJCSIS) International Journal of Computer Science and Information Security, Vol. 10, No. 3, March 2012 ep ii) Double Ste Tapering III. ION RESULT & CONCLUSI The schematic of double ste tapering is s c ep shown in Fig 7 T The total sim mulation proce ne ess was don by CST which two step of 10 mm are used. in w ps e Micr hat rowave Studio. It is infer th Tapering b between two waveeguides is go ood possible solution to c connect two wave ed lent eguides. Tapere waveguide offer an excell means of verting microw conv zes wave mode siz to connect microwave ces devic of different cross-sectio ons. Properly onal dimensio e single stepping with 10 mm s size with wave is guided in s g step no r waveguide. Im reflection in w mpedance matching is the or h mino problem with double step. EDGMENT ACKNOWLE The e Dr. T authors are grateful to D R.C Sethi, HOD,EXTC TEC and Prof. Mrs. Jyothi Digge, PG coordinator, e g Fig 7 - Double Step Tapering EXT eir ort ble TC,TEC for the great suppo and valuab guidance. y They would also like to ackno p owledged help & support 21 tion are shown Their S11, S2 plots and E field distribut n ived from Dr. Abhay Deshpande, Scientist, recei Figs . m in F 8, 9 &10. In double step tapering from Fig 8 & 9 it t SAMMEER,IIT-B. ows sho that imped g urs. dance matching problem occu Due to this s ve ed om l wav is not guide properly fro cylindrical waveguide to o tangular waveg rect guide. NCES REFERN  Chen Huaibi, Hua Yuanzhong, L Yuzheng, Ton Dechun, Ding C ang Lin ng Xiaodong Departm X ing ment of Engineeri physics, Tsing ghua University, Beijing 100084, B B BACKWARD TR VE RAVELING WAV ELECTRON LINAC, 1998 IEE L EE  J Petillo, W. Krueger, A. M J. Mondelli, “Frequ uency Domain D Determination of the Waveguide Lo SSCL Drift Tube oaded Q for the S Linac” IEEE Particle accelerator con L nference 1993.  M ulla wi Muralidhar Yeddu , Sami Tantaw , SLAC, Menlo Park, “Analysis o a Compact Circ of cular TE0,1 - Rec Waveguide Mode ctangular TE0,2 W pering Fig 8 - S11 plot for double step tap Converter”, Proce C 07, , eedings of PAC0 Albuquerque, New Mexico, USA, 2007,pp-587 U 7-589  L. L Solymar, “Spur rious mode gener orm ration in nonunifo waveguide,” IRE Transactions on Microwave Th I heory and Techniq ques, vol. MTT- 7, 7 pp. 379–383, 19 959.  Dr. c,” F 0 D R.C.Sethi etc Design of RF structure for 10 MeV,10 KW, I tron linac. Industrial RF elect  P. va, P K. Jana, Purushottam Shrivastav Nita. S. Kulka arni, “Design of M er Microwave Couple for 10 MeV Ele ectrons LINAC” Fig 9 - S21 plot for double step tap pering Fig 10 - E F ion step Field Distributi in Double s tapering 66 http://sites.google.com/site/ijcsis/ ISSN 1947-5500
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