Comparative Analysis of Rectangular Waveguide and Coaxial Cable Using H.F.S.S

Transcription

1 Comparative Analysis of Rectangular Waveguide and Coaxial Cable Using H.F.S.S SK Masud Hossain1, Syed Mahammad Ashif1, Subhajit Ghosh1, Diptyajit Das2, Samsur Rahaman3 1Department of Electronics and Communication Engineering, WBUT, Kolkata, India, 2Department of Bio Medical Engineering, WBUT, Kolkata, India, 3Department of Electronics and Communication Engineering, Bengal Engineering & Science University, Shibpur,India Abstract This paper proposes new designs to eliminate attenuations present in the transmission line by means of perfect matching of the ports through two models - coaxial cable and rectangular waveguide. This paper also depicts the various conditions for propagation of waves through the structures. Keywords Lumped Port, Wave Port, Standing wave pattern, Perfect Matching, E & H field. 1. INTRODUCTION Coaxial cable is a type of cable for high bandwidth data transmission use that typically consists of a single copper wire that is surrounded by a layer of insulation and then by a grounded shield of braided wire or an extruded metal tube. The whole thing is usually wrapped in another layer of insulation and, finally, in an outer protective layer. The grounded metal tube or braided wire shield minimizes electrical interference and radio frequency interference (RFI) and results in a much greater bandwidth (i.e., data transmission capacity) than does conventional copper wire cable (but less than optical fiber cable). The metal tube type has a greater data transmission capacity but is rigid and thus is used only for specials situations; the braided type is much more flexible and easier to use. Connections to the ends of coaxial cables are usually made with specially designed RF (radio frequency) connectors. Whereas waveguides are used principally at frequencies in the microwave range; inconveniently large guides would be required to transmit radiofrequency power at longer wavelengths. In the X- Band frequency range of 8.2 to 12.4 GHz, for example, the U.S. standard rectangular waveguide, WR-90, has an inner width of cm (0.9 in.) and an inner height of cm (0.4 in.). Rectangular waveguides are commonly used for power transmission at microwave frequencies. Their physical dimensions are regulated by the frequency of the signal being transmitted. In this paper we discuss various criteria for propagation of the waves through coaxial cable and rectangular waveguide. The paper depicts the perfect modeling of coaxial cable and rectangular waveguide for perfect propagation of waves and without any distortion or attenuation. 2. A. Coaxial Cable Model 2. MODEL ANALYSIS 2. A.1.Design. Coaxial cable is a self-shielded cable used for transmission of communications signals, such as those for television, telephone, or computer networks. A coaxial cable consists of two conductors laid concentrically along the same axis. One conducting wire is surrounded by a dielectric insulator, which is in turn surrounded by the other, outer conductor, producing an electrically shielded transmission circuit. The whole cable is wrapped in a protective plastic sheathing. The signal propagates within the dielectric insulator, while the associated current flow is restricted to adjacent surfaces of the inner and outer conductors. Our design is a coaxial cable of length l=200 mm, inner radius r1= mm, intermediate radius r2= mm, outer radius=2.5 mm. The substrate is kept between inner and outer cylinders and it has a dielectric constant r of 1.9. The frequency of operation is fixed about 4 GHz. Fig.1 Designed Diagram of Coaxial cable. ISSN: Page 267

2 2. A.2.Observations. We observed the E & H field and the direction of propagation of wave along a line created just above the inner cylinder when all the afore mentioned aspects are gratified. Fig. 2 Line of observation in between the inner and outer cylinder. 2. A.2.1. BOTH PORTS ARE MATCHED AND HAVE RESISTANCE 50 OHMS After both the ports are matched perfectly and are assigned resistances of 50Ωs in each port,we observed E-field along Y-axis, H-field along X-axis and full transmission happens with no attenuation or very little attenuation in the Z direction. The wave behavior is presented in sequential order. Fig. 3 Schematic diagram represents wave propagation in different 2. A.2.2 PORT 2 IS ASSIGNED WITH LUMPED PORT AND ALLOTED A RESISTANCE OF mω (VERY LOW RESISTANCE). When port1 is assigned a resistance of 50Ωs and port2 of 0.005mΩ we observed E-field along Y-axis, H-field along X-axis but no propagation of wave in the cable and a standing wave pattern is observed. The wave manner is displayed in a sequential order. ISSN: Page 268

3 Fig. 5 Schematic diagram represents wave propagation in different 2. B. Rectangular Waveguide Model Fig. 4 Schematic diagram represents wave propagation in different 2. A.2.3 PORT 2 IS ASSIGNED WITH LUMPED PORT AND ALLOTED A RESISTANCE OF 1400 MΩ (VERY HIGH RESISTANCE). When port1 is assigned a resistance of 50Ωs and port2 of 1400 MΩ again we observed E-field along Y-axis, H-field along X-axis but no propagation of wave and a standing wave pattern is observed. The wave behavior is shown in sequential order 2. B.1.Design. In general, a waveguide consists of a hollow metallic tube of arbitrary cross section uniform in extent in the direction of propagation. Common waveguide shapes are rectangular, circular, and ridged. The rectangular waveguide has a width a and height b as shown in figure. In our design inside a cuboid another cuboid is placed and the cavity is kept hollow. In this model length l=100mm, width a=0.9 inch, height b= 0.4 inch and thickness t= 2 mm. Substrate is not used in this model and the frequency of operation is set at 10GHz. ISSN: Page 269

4 Fig. 6 Designed diagram of rectangular waveguide. 2. B.2.Observations. We observed the E & H field and the direction of propagation of wave along an experimental vertical plane when all the afore mentioned aspects are satisfied. Fig.7 Observation along experimental vertical plane for the above condition. 2. B.2.1 BOTH PORTS ARE MATCHED AND ASSIGNED RESISTANCES OF 50 OHMS When observed along any experimental vertical plane, we get the following wave pattern. We can observe-e-field along Y-direction, H-field along X- direction and the wave propagates in z direction with no attenuation or very tiny attenuation. The wave behavior is presented in successive order. Fig.8 Schematic diagram represents wave propagation in different 2. B.2.2 PORT 2 IS ASSIGNED WITH LUMPED PORT AND ALLOTED A RESISTANCE OF mω (VERY LOW RESISTANCE). Very similarly in this case when port1 is assigned a resistance of 50Ωs and port2 of 0.001mΩ we can observe E-field along Y-axis, H-field along X-axis but no propagation of wave and a standing wave pattern is observed. The wave actions are shown in sequential order. ISSN: Page 270

5 3. CONCLUSION All the above results have been done in Ansoft H.F.S.S 11.0 wbb version. By regulating the frequency of the transmitted signal and by means of perfect matching of wave ports a signal can be transmitted all through the transmission lines and wave guides without any distortion. In waveguides the electric and magnetic fields are confined to the space within the guides. Thus no power is lost to radiation. Since the guides are normally filled with air, dielectric losses are negligible. However, there is some I2R power lost to heat in the walls of the guides, but this loss is usually very small. 4. REFERENCES Fig.9 Schematic diagram represents wave propagation in different 2. B.2.3 PORT 2 IS ASSIGNED WITH LUMPED PORT AND ALLOTED A RESISTANCE OF 2000 MΩ (VERY HIGH RESISTANCE). Very similarly in this case when port1 is assigned a resistance of 50Ωs and port2 of 2000 MΩ we can observe E-field along Y-axis, H-field along X-axis but no propagation of wave and a standing wave pattern is observed. The wave behavior is shown in sequential order. [1] D.M.Pozar, 2005, Microwave Engineering John Wiley and Sons. [2] Karle S. Packard The Origin of Waveguides: A Case of Multiple Rediscovery IEEE transactions on Microwave theory and techniques, vol. mtt-32, no.9, September [3] L.V. Blake. Transmission Lines and Waveguides, Wiley: New York, [4] H.J OUYANG, F.W WILLIAMS and D. KENNEDY 0883 Journal of Sound and Vibration, A general method for analyzing wave propagation along longitudinally periodic structures. [5] N. S. Nahman, A discussion on the transient analysis of coaxial cables considering high-frequency losses, IRE Trans. Circuit Theory, vol. 9,pp , Jun [6] D. R. Holt and N. S. Nahman, Coaxial-line pulse-response error dueto a planar skin-effect approximation, IEEE Trans. Instrum. Meas.,vol. IM- 21, no. 4, pp , Nov [7] L. BRILLOUIN 1953 Wave Propagation in Periodic Structures. New York:Dover. [8] D. J MEAD 1975 Journal of Sound and Vibration 40,1-18. Wave propagation and natural modes in periodic systems, I: mono-coupled systems Fig.10 Schematic diagram represents wave propagation in different ISSN: Page 271