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Due to the enormous performance gains associated with the use of antenna arrays in wireless networks, it is inevitable that these technologies will become an integral part of future systems. This report focuses on signal propagation modeling for antenna array systems and on its relationship to the performance of these systems. Accurate simulation and analytical models are prerequisite to the characterization of antenna array system performance. Finally, an understanding of the performance of these systems in various environments is needed for effective overall network design. This report begins with an overview of the fundamentals of antenna array systems. A survey of vector channel models is presented. Angle of arrival and time of arrival statistics for the circular and elliptical (Liberti's Model) models are derived. A generalized optimum output SINR analysis is derived for space-time processing structures in frequency selective fading channels. The hardware and software of the MPRG Antenna Array Testbed (MAAT) is described. A literature review of previous antenna array propagation measurements is given. Antenna array measurement results obtained with the MAAT are used to compare the properties of the received signal vector in the various environmental conditions. The influence of channel parameters on the ability of antenna arrays to separate the signals of two users on the reverse link is studied using simulation. Finally, forward link beamforming techniques are reviewed. / Ph. D.

Methods of expressing the radiation patterns of phased arrays in closed form that include the effects of radiated mutual coupling are investigated. The two basic methods considered are the classical array analysis method and the active element pattern methods. The theoretical derivations of the active element pattern methods are presented and the various types of active element patterns are defined. Also, a new method based on active element patterns, the hybrid active element pattern method, is introduced which accurately predicts the patterns of small and moderately-sized arrays of equally-spaced elements. Arrays of center-fed dipoles are considered in this study since dipole arrays can be fully characterized, including mutual coupling, using modem numerical electromagnetic analysis codes, thus allowing verification of the array analysis methods presented here. The results are general, however, and may be applied to arrays of any type of element. The array patterns computed using the classical analysis method and the active element pattern methods are compared to those computed using ideal array analysis and the highly-accurate numerical codes. / Master of Science

Design of antenna arrays for present day requirements has to take into account both mechanical and electrical aspects. Mechanical aspects demand the antennas to have low profile, non-protruding structures, structures compatible to aerodynamic require­ments and so on. Electrical aspects may introduce several constraints either due to. technical reasons or due to readability conditions in practice. Thus, arrays of modern requirements may not fall into the category of linear or planar arrays. Further, due to the nearby environment, the elements will generate complicated individual patterns. These issues necessitate the analysis and synthesis of antenna arrays which are arbi­trary as far as the orientation, position or the element pattern are concerned. Such arrays which may be called arbitrary arrays are being investigated in this thesis. These investigations have been discussed as different aspects as indicated below: Radiation Characteristics of Arbitrary Arrays Radiation fields of an arbitrarily oriented dipole are obtained. Such fields are plotted for typical cases. Further, methods for transforming the electromagnetic fields are discussed. Having obtained the field due to an arbitrary element, the fields due to an arbitrary array are obtained. Factors controlling the radiation fields, like, the curvature in the array and element pattern are investigated. Radiation patterns of circular and cylindrical arrays are plotted. Synthesis of a Side Lobe Topography Requirements of a narrow beam pattern generated by an antenna array are identified. A problem of synthesizing such a pattern using an arbitrary array is formulated. The envelope of the side lobe region which may be called, the side lobe topography (sit), is included in the computation of the covariance matrix. This problem which has been formulated as a problem of minimizing a quadratic function subjected to a system of linear constraints is solved by the method of Lagrangian multipliers. An iterative procedure is used to satisfy all the requirements of the pattern synthesis. The procedure has been validated by synthesizing linear arrays and is used to synthesize circular and parabolic arrays. Patterns with tapered sit, Taylor-like sit have been synthesized. Asymmetric patterns are also synthesized. Role of sit is brought out. Shaped Beam Synthesis Synthesis of shaped broad beams is discussed. Amplitude constraints are formulated. Phase distribution is linked with the phase centre. Quadratic problems thus formu­lated are solved by the Lagrangian method of undetermined multipliers. An iterative procedure is made use of to synthesize flat topped beams as well as cosecant squared-patterns using linear arrays as well as circular arrays. Reasonable excitation dynamic has been obtained. Optimum phase centres obtained by trial and error are made use of. Effects of the Frequency and Excitation on the Synthesized Patterns In general, synthesized patterns can be sensitive towards any specific parameter either excitation or to frequency or any such parameter. Several methods can be used to observe these issues. In this thesis, these effects are also studied. Using a specific array configuration, to synthesize a specified radiation pattern, frequency is changed by 10% from the design frequency and the pattern is computed. Similarly, excitation phase distribution is rounded to the nearest available phase distribution using a digital phase shifter (say 8 bit) and the resulting pattern is computed. Further, excitation dynamic is also controlled by boosting the amplitudes of the array elements which are less than the permissible (i.e. the maximum excitation/allowed dynamic). Effects of these variations are also recorded. It appears that reasonable patterns can be obtained, in spite of significant variations in these parameters in most of the cases. Reconfigurable Arbitrary Arrays It would be very useful if a single array configuration can be used for different ap- plications. This may be either for the different phases of a single application or for different applications that may be required at different times. Attempts are made to synthesize a variety of patterns from a single array. Such arrays which may be called as reconfigurable arrays can be of much use. Obviously, the excitations are different for different patterns. Both narrow beams, as well as shaped broad beams, with different side lobe topographies have been synthesized using a single array.

Thesis (MScIng)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: The quadrifilar helix antenna has frequently been employed to provide the wide angle, circularly polarized radiation pattern which is preferable for mobile satellite communications. A detailed study of this antenna and its varieties is presented. When used as an element in wide angle scanning arrays for aeronautical satellite tracking applications, the additional requirement of a low profile with light weight applies. This further complicates the realization of good circular polarization close to the horizon. A top disk is incorporated into various antenna structures in an effort to improve the radiation performance when used within a closely spaced array while reducing the height of the radiating element. The array performance of these elements are investigated which hints at a supported traveling mode aiding the ability to accomplish the wide angle beam steering. Subsequent study of leakywave antennas initiated the study and implementation of leaky-wave structures in phased arrays of quadrifilar helix elements. / AFRIKAANSE OPSOMMING: Die vierledige heliksantenna word dikwels gebruik vir toepassings wat ’n wye, sirkulêr gepolariseerde stralingspatroon benodig. ’n Verskeidenheid van hierdie antennas is noukeurig bestudeer en hul toepaslikheid vir mobiele sattelietkommunikasie ondersoek. Wanneer hierdie antennas in fase gestuurde skikkings gebruik word, word dit ook vereis dat die eenhede liggewig is met ’n lae profiel. Dit bemoeilik die verkryging van goeie sirkulêre polarisasie naby die horison aansienlik. In ’n poging om die wyehoek straling met kort antennas te verbeter, is ’n oorhoofse skyf tot verskillende heliksstrukture toegevoeg. In nou gespasieerde skikkings maak hierdie skywe ’n positiewe bydrae to wyehoekstralingeienskappe. Die invloed van lekmodusse wat binne die struktuur voortplant is ondersoek en gebruik in skikkings waarvan die bundel naby aan die horison gestuur word.

Lee Wai Ki. / Thesis submitted in: May 2004. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 62-66). / Abstracts in English and Chinese. / Chapter Chapter 1: --- Introduction --- p.8 / Chapter 1.1 --- Motivation --- p.8 / Chapter 1.2 --- Organization of the thesis --- p.10 / Chapter Chapter 2: --- Background Technology --- p.12 / Chapter 2.1 --- Introduction: FUZZY EM CAD formula for impedance of the edge of the patch antenna --- p.12 / Chapter 2.2 --- Fringe field extension of the patch: --- p.12 / Chapter 2.2.1 --- Applying the root of area capacitance formula --- p.12 / Chapter 2.2.2 --- Defining microstrip parallel plate capacitor with infinite substrate --- p.13 / Chapter 2.2.3 --- The parallel plate capacitor formula --- p.14 / Chapter 2.2.4 --- DC fringe field leading to the patch extension --- p.15 / Chapter 2.3 --- Cavity model of the patch --- p.16 / Chapter 2.3.1 --- Cavity model analysis on its internal field --- p.16 / Chapter 2.3.2 --- Input impedance derived from cavity model --- p.19 / Chapter 2.3.3 --- Quality factor of patch antenna --- p.19 / Chapter 2.4 --- Fringe extension applied to cavity model in RF --- p.23 / Chapter Chapter 3: --- Simple one Port wide band multi-layer patch Antenna --- p.24 / Chapter 3.1 --- Introduction --- p.24 / Chapter 3.2 --- Antenna design --- p.25 / Chapter 3.3 --- Measured results --- p.26 / Chapter 3.4 --- Antenna Analysis --- p.29 / Chapter 3.5 --- Conclusion --- p.30 / Chapter Chapter 4: --- Design synthesis of patch antennas of the T-square Probe --- p.31 / Chapter 4.1 --- Introduction --- p.31 / Chapter 4.2 --- The physics interpretation --- p.32 / Chapter 4.3 --- The Smith chart movement by the T-square feed on the patch --- p.33 / Chapter 4.4 --- Conclusion --- p.35 / Chapter Chapter 5: --- Design synthesis of the wideband tuning-fork-shaped feeding for patch antenna --- p.36 / Chapter 5.1 --- Introduction --- p.36 / Chapter 5.2 --- Antenna design --- p.36 / Chapter 5.3 --- The Smith chart movements of the tuning-fork shaped feeding on the patch --- p.37 / Chapter 5.4 --- Conclusion --- p.41 / Chapter Chapter 6: --- "Fork on H-slot feed of multilayer microstrip antenna for wideband, high isolation and low cross polarization" --- p.42 / Chapter 6.1 --- Introduction --- p.42 / Chapter 6.2 --- Antenna analysis - Isolation improvement considerations --- p.44 / Chapter 6.3 --- Antenna design and measured results --- p.46 / Chapter 6.3.1 --- The simulated return loss and current distribution s in various structure of the two port. --- p.47 / Chapter 6.3.2. --- The hardware and the comparison of results --- p.50 / Chapter 6.3.3. --- The simulated properties of the radiation patterns and cross-polarizations --- p.52 / Chapter 6.3.4. --- The comparison of radiation patterns between simulation and hardware --- p.56 / Chapter 6.4 --- Further improvements --- p.58 / Chapter 6.5 --- Conclusion --- p.59 / Chapter Chapter 7: --- Conclusions --- p.60 / Reference --- p.62 / List of Publication --- p.66

This dissertation investigates the use an array of active nonlinear elements, with particular emphasis on controlling distortion products generated by nonlinear elements in space rather than using conventional ways such as transmission lines, waveguides, and power dividers and combiners. The nonlinear elements are made of assemblies of antennas and electronic switches, called modulated scatterers (MSs). These so-called MSs elements are utilized in a wide variety of applications such as radio frequency identification (RFID) systems, microwave imaging, Internet-of-Things sensors, etc. However, no research work has been reported in the literature regarding exploiting and controlling several distortion products generated by MSs at the same time according to the best of authors' knowledge. To facilitate controlling distortion products which means suppressing or enhancing distortion products in space, we present a nonlinear array with elements that are MSs instead of conventional antennas. MSs are switched ON-OFF at different times by modulation signals having the same frequency. The time delay of the switching process between array elements represents a relative phase shift difference in the frequency domain. Thus, the presented structure is called the phase-modulated scattering array (PMSA). The PMSA has a similar layout of phased arrays, but it does not have a feeding network and is fed by an external source called the illuminating source. Because our system does not need a feeding network and phase shifters, it is potentially easier to implement with low cost. Two different signals which are the illuminating (incident) and modulation signals interact inside switches to generate a huge number of distortion products due to the nonlinearity of switches and the periodic nature of the presented system. Distortion products then leave the presented PMSA to space again (i.e., scattering distortion products). The PMSA is able to treat distortion products and achieve beamforming functions. The operation mechanism of the PMSA is explained by developing two different mathematical models. Communication signal processing perspectives are the basis of the first mathematical model developed to show the spatial characteristics of distortion products generated by our presented PMSA. Its root is originated from a mathematical model of the widely-used polyphase multipath technique in RF communication circuits. However, the adopted technique is suitable only for communication circuits with a single output and parameters prescribed in advance. Thus, the model is further developed to circumvent all the problems mentioned above and to be able to detect the spatial characteristics of distortion products at any point in space. Static impacts of the measurement environment, real radiation patterns of actual antennas utilized in prototypes, and phase and gain errors among paths have been taken into account as well. In the model, every single scatterer is represented by a single separate path. Furthermore, the modified model is extended to include single, two, and multi tones modulation signals. Simulation results have been obtained before and after the modification for a different number of paths and modulation signals with different tones. Results show that the modified model can quantify spatial characteristics of distortion products at any point in space where specific distortion products are enhanced, and others are canceled. Because distortion products are independent in their nature (i.e., each single distortion product has different frequency and phase), they have independent radiation patterns (scattered beams). Therefore, the second mathematical model based on phased antenna array perspectives is developed. The relationship between the two models states that a distortion product which is enhanced at a certain point in space has a maximum scattered beam at that point. Also, the second mathematical model being similar to mathematical models of phased arrays considers effects of all distortion products resulting from single, two, and multi tones modulation signals, and it states that each single distortion component has its particular scattered beam. Next, sub-models for some properties and applications of the presented PMSA such as a diffraction grating-like behavior, nonreciprocity, beamforming, a tool for distortion product analysis of phased arrays and multi-input multi-output (MIMO systems), a reconfigurable-spatial harmonic generator, and a direction finding technique are derived depending on the two main mathematical models. All parts are simulated and results validate all proposed functionalities. Single antennas, antenna arrays, electronic switches (modulators), and a 4-to-8 phase transformer kit using only resistors have been designed, simulated, fabricated, assembled, and tested. Eventually, different structures of the presented PMSAs working at 432MHz and 2.3GHz are tested inside the anechoic chamber. Both frequencies are downconverted to the band 2-22kHz. Modulation signals used in the experimental setups are single and two tones. Data are measured using the commercial software SigView running on a laptop and a spectrum analyzer. Both spatial characteristics and scattered beams of distortion products are measured. Comparisons have been made between measured received responses of scattered signals and theoretical results. They are in good agreement although limitations and challenges are encountered with each round of measurement. Measured results confirm practically that as a number of scatterers increases, more distortion products are controlled at the same time. The distortion product rejection ratio DPRR is more than 15dB for all measured distortion products supposed to be canceled. Directions of scattered beams are found at expected locations with errors less than 3%. Furthermore, directions of illuminating signals or distances separating between PMSA elements are varied to change directions of scattered beams when prescribed values of parameters governing the overall performance are being broken. In other words, the beamforming functionality has been validated practically. Different elements of 8*1-PMSA are turned-off at measurements in order to find fault tolerances of the presented system. Measured results show that when two elements are failed simultaneously, responses can be accepted to some extent.