International Journal of Electrical & Electronics Research (IJEER) Volume 3 issue 3, Pages 50-53, September 2015, ISSN: 2347-470X 50 CASCADING OF TWO RECTANGULAR WAVEGUIDES BY USING HFSS, CASCADE AND MATLAB SOFTWARE Hemant Singh Pokhariya*, Sourabh Bisht**, Vikas Rathi*** *, **, *** Department of Electronics & Communication Engineering, Graphic Era University Dehradun, India 1 hemantdoon86@gmail.com, 2 sourabh_bisht2002@yahoo.com, 3 Vikas.Rth@gmail.com ABSTRACT- This project studies the analysis of cascading of two rectangular waveguide of different cross-Section It also shows how to combine all the scattering matrices of a microwave circuit to obtain its overall scattering parameters of the circuit .Simulation of cascading of two rectangular waveguide with different dimensions by using HFSS and computer program in MATLAB is developed to calculate the S parameter of cascaded two rectangular waveguide. Finally above these two results are compared with the results obtained from the CASCADE. CASCADE is a highly efficient and accurate tool for designing 2-port waveguide components, RF windows, and waveguide systems. The program is very user-friendly and executes very rapidly on standard personal computers. Keywords- Junction Discontinuities, Scattering Matrix, Reflection coefficient, Transmission Coefficient. 1. INTRODUCTION A closed waveguide is an electromagnetic waveguide that is tubular, usually with a circular or rectangular cross section, has electrically conducting walls that may be hollow or filled with a dielectric material, can support a large number of discrete propagating modes, though only a few may be practical in which each discrete mode defines the propagation constant for that mode, in which the field at any point is describable in terms of the supported modes In this there is no radiation field, and discontinuities and bends cause mode conversion but not radiation. The dimensions of a hollow metallic waveguide determine which wavelengths it can support, and in which modes. Typically the waveguide is operated so that only a single mode is present. The lowest order mode possible is generally selected. Frequencies below the guide's cutoff frequency will not propagate. It is possible to operate waveguides at higher order modes, or with multiple modes present, but this is usually impractical. Waveguides are almost exclusively made of metal and mostly rigid structures. Figure 1. Geometry of a Waveguide 2. WAVEGUIDE IN PRACTICE AND MODAL EXPANSION IN WAVEGUIDES In practice, waveguides act as the equivalent of cables for super high frequency (SHF) systems. For such applications, it is desired to operate waveguides with only one mode propagating through the waveguide. With rectangular waveguides, it is possible to design the waveguide such that the frequency band over which only one mode propagates is as high as 2:1 (i.e. the ratio of the upper band edge to lower band edge is two). The relationship between the longest wavelengths that will propagate through a rectangular waveguide is a simple one. Given that W is the greater of its two dimensions, and lambda is the wavelength, then lambda = 2W. Because rectangular waveguide have a much larger bandwidth over which only a single mode can propagate, standards exist for rectangular waveguides, but not for circular waveguides. In general (but not always), standard waveguides are designed such that one band starts where another band ends, with another band that overlaps the two bands the lower edge of the band is approximately 30% higher than the waveguide's cutoff frequency the upper edge of the band is approximately 5% lower than the cutoff frequency of the next higher order mode the waveguide height is half the waveguide width. 3. WAVEGUIDE DISCONTINUITES The abrupt changes in a waveguide will give rise to a discontinuity that will create standing waves. The basic concept of the mode matching algorithm will lead to an accurate method for analyzing the propagation characteristics of wave guide discontinuities. Discontinuities in dielectric waveguides play an important role in designing components in millimeter, sub millimeter and optical circuitry. Quit often in these applications an open waveguide with one particular cross-section must be joined to a waveguide of another cross-section. The open waveguides to be connected differ sometimes not only in size but also in their cross-sectional form. Usually these waveguide connectors are required to launch as much as possible of the power that is incident in one waveguide into the other waveguide. In such waveguide transitions power may be lost to reflection and radiation. The transition should be designed to keep radiation reflection loss at a minimum. Transitions between different dielectric waveguides in form of gradual waveguide tapers are particularly well suited for open waveguides because of their microscopic dimensions. An