Waveguide Literature Review

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CHAPTER 2 LITERATURE REVIEW 2.1 Substrate Integrated Waveguide (SIW) Substrate Integrated Waveguide (SIW) is a new form of transmission line and new technology in the communication system. This waveguide is manufactured within a substrate. In designing the structure of SIW waveguide, the dimension is similar to the rectangular waveguide (RGW) in a planar form. The difference between the both structures is that the SIW having two parallel arrays of via or holes as the electrical walls while the RWG waveguide make the substrate as the wall. The SIW is the intermediate structure of the microstrip line and the metallic waveguide. It benefits from a low cost production but can achieve high power-handling capabilities and co-planar integration [1].…show more content…
The components of SIW waveguide are compact, light and flexible makes the SIW waveguide easy to design and fabricate. The dominant mode cut-off frequency of SIW waveguide is same as TE10 mode of rectangular waveguide [2]. The key parameter in designing the SIW are the spacing between the via “p” also called as pitch, diameter of via “d”, central distance between via arrays “Ar” and the equivalent width “Ae” as shown in Figure 2.1. Figure 2.1: SIW to microstrip transition design scheme and key parameters The SIW parameter should be designed carefully. The pitch, p and the diameter, d control the radiation loss and return loss respectively. If the distance between the “p” is less than or equal to the twice of “d”, then the leakage losses is negligible. The integrated waveguide width, “Ar” determines the cut-off frequency and propagation constant of the fundamental mode [3]. There are two design rules related to the pitch and the via diameters…show more content…
The taper is used to transform the quasi-TEM mode of the microstrip line into the TE10 mode in the waveguide. The microstrip line is suited well with the rectangular waveguide because they have the same profile of the electric field orientation. This is shown in Figure 2.2. Figure 2.2: Dominant modal electric filed profiles (a) in rectangular waveguide and (b) in microstrip line [5]. The key parameter in designing the taper are the length of the taper, “l” and the width, “w” of the taper at the SIW end. A large different between these two widths will result a long taper. In order to minimize the return loss, the taper length must be multiple of a quarter of a wavelength. The width of the taper line can be found [2]: 120Π/ηH[W/H+ 1.393+0.667 ln⁡(W/H+ 1.444) ] = 4.38/Ae e^(-0.627 εr/((εr+1)/2+ (εr-1)/√(2&1+ 12H/W))) (2.10) Where Ƞ is the free space intrinsic impedance having value of 377 ohm. The taper length is given by: L= nλg/4, n=1,2,3,4…….. and λg= c/(f√εr)
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