Ali Mohamed Ali Sayed Ahmed, Ahmed. On the development of novel multilayer passive components and the implementation of compact wideband twolayer 4x4 Butler matrix in SIW technology. PhD, Institut National Polytechnique de Toulouse, 2010

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Official URL: http://ethesis.inptoulouse.fr/archive/00001236/
Abstract
Multibeam antennas have become a key element in nowadays wireless communication systems where increased channel capacity, improved transmission quality with minimum interference and multipath phenomena are severe design constraints. These antennas are classified in two main categories namely adaptive smart antennas and switchedbeam antennas. Switchedbeam antennas consist of an elementary antenna array connected to a Multiple Beam Forming Network (MBFN). Among the different MBFNs, the Butler matrix has received particular attention as it is theoretically lossless and employs the minimum number of components to generate a given set of orthogonal beams (provided that the number of beams is a power of 2). However, the Butler matrix has a main design problem which is the presence of path crossings that has been previously addressed in different research works. Substrate Integrated Waveguide (SIW) features interesting characteristics for the design of microwave and millimetrewave integrated circuits. SIW based components combine the advantages of the rectangular waveguide, such as the high Q factor (low insertion loss) and high power capability while being compatible with lowcost PCB and LTCC technologies. Owing to its attractive features, the use of SIW technology appears as a good candidate for the implementation of BFNs. The resulting structure is therefore suitable for both waveguidelike and planar structures. In this thesis, different novel passive components (couplers and phase shifters) have been developed exploring the multilayer SIW technology towards the implementation of a twolayer compact 4×4 Butler matrix offering wideband performances for both transmission magnitudes and phases with good isolation and input reflection characteristics. Different techniques for the implementation of wideband fixed phase shifters in SIW technology are presented. First, a novel waveguidebased CRLH structure is proposed. The structure is based on a singlelayer waveguide with shunt inductive windows (irises) and series transverse capacitive slots, suitable for SIW implementations for compact phase shifters. The structure suffers relatively large insertion loss which remains however within the typical range of nonlumped elements based CRLH implementations. Second, the wellknown equal length, unequal width SIW phase shifters is discussed. These phase shifters are very adapted for SIW implementations as they fully exploit the flexibility of the SIW technology in different path shapes while offering wideband phase characteristics. To satisfy good return loss characteristics with this type of phase shifters, the length has to be compromised with respect to the progressive width variations associated with the required phase shift values. A twolayer, wideband lowloss SIW transition is then proposed. The transition is analyzed using its equivalent circuit model bringing a deeper understanding of its transmission characteristics for both amplitude and phase providing therefore the basic guidelines for electromagnetic optimization. Based on its equivalent circuit model, the transition can be optimized within the well equallength SIW phase shifters in order to compensate its additional phase shift within the frequency band of interest. This twolayer wideband phase shifter scheme has been adopted in the final developed matrix architecture.This transition is then exploited to develop a threelayer, multiplyfolded waveguide structure as a good candidate for compensatedlength, variable width, lowloss, compact wideband phase shifters in SIW technology. Novel twolayer SIW couplers are also addressed. For BFNs applications, an original structure for a twolayer 90° broadband coupler is developed. The proposed coupler consists of two parallel waveguides coupled together by means of two parallel inclinedoffset resonant slots in their common broad wall. A complete parametric study of the coupler is carried out including the effect of the slot length, inclination angle and offset on both the coupling level and the transmission phase. The first advantage of the proposed coupler is providing a wide coupling dynamic range by varying the slot parameters allowing the design of wideband SIW Butler matrix in twolayer topology. In addition, previously published SIW couplers suffer from direct correlation between the transmission phase and the coupling level, while the coupler, hereby proposed, allows controlling the transmission phase without significantly affecting the coupling level, making it a good candidate for BFNs employing different couplers, such as, the Nolen matrix. A novel dualband hybrid ring coupler is also developed in multilayer Ridged SIW (RSIW) technology. This coupler has been jointly developed with Tarek Djerafi in a collaboration scenario with Prof. Ke Wu from the Ecole Polytechnique de Montréal. The coupler has an original structure based on two concentric rings in RSIW topology with the outer ring periodically loaded with radial, stubloaded transverse slots. A design procedure is presented based on the Transverse Resonance Method (TRM) of the ridged waveguide together with the simple design rules of the hybrid ring coupler. A C/K dual band coupler with bandwidths of 8.5% and 14.6% centered at 7.2 GHz and 20.5 GHz, respectively, is presented. The coupler provides independent dual band operation with lowdispersive wideband operation. Finally, for the Butler matrix design, the twolayer SIW implementation is explored through a twofold enhancement approach for both the matrix electrical and physical characteristics. On the one hand, the twolayer topology allows an inherent solution for the crossing problem allowing therefore more flexibility for phase compensation over a wide frequency band. This is achieved by proper geometrical optimization of the surface on each layer and exploiting the SIW technology in the realization of variable width waveguides sections with the corresponding SIW bends. On the other hand, the twolayer SIW technology is exploited for an optimized space saving design by implementing common SIW lateral walls for the matrix adjacent components seeking maximum size reduction. The two corresponding 4×4 Butler matrix prototypes are optimized, fabricated and measured. Measured results are in good agreement with the simulated ones. Isolation characteristics better than 15 dB with input reflection levels lower than 12 dB are experimentally validated over 24% frequency bandwidth centered at 12.5 GHz. Measured transmission magnitudes and phases exhibit good dispersive characteristics of 1dB, around an average value of 6.8 dB, and 10° with respect to the theoretical phase values, respectively, over the entire frequency band.
Item Type:  PhD Thesis 

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Institution:  Université de Toulouse > Institut National Polytechnique de Toulouse  INPT 
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Research Director:  Aubert, Hervé 
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