Browsing by Subject "Antennas (Electronics)"

Now showing 1 - 6 of 6
  • Thumbnail Image
    ItemOpen Access
    Analysis and design of broadcast tower antenna systems
    (2014) Ali Abdul
    In broadcasting, the coverage and interference requirements of antennas are designated in terms of Effective Radiated Power (ERP), tower location and height, and antenna patterns. When antennas are tailored to satisfy the requirements, transmitter powers, cable losses, and phase adjustments for antenna elements must be taken into account in addition to the parasitic effect of the supporting and nearby towers on characteristics of antenna. Digital video and audio broadcasting requires antennas to be at least 95 % effi- cient, wideband, low weight and high gain with enhanced radiation performance. For this reason many wire and planar antennas have been designed to meet the requirement of Digital Video Broadcasting-Terrestrial (DVB-T) and TerrestrialDigital Audio Broadcasting (T-DAB). We used a tool NEC (Numerical Electromagnetic Code) to model antenna on top of a tower structure. Simulation results for parasitic effect of the tower on characteristics of antenna such as impedance, return loss, gain, front-to-back ratio and radiation patterns are reported. In addition, the effect of nearby tower on antenna characteristics is studied. We designed a broadband antenna in the UHF (470 - 860 MHz) band that works for both digital and analog TV with return loss ≥10 dB, fractional bandwidth of 85% and gain at center frequency 12.5 dB. The ERP is calculated by mounting the antenna at each face of the tower to give a satisfactory coverage to a region around the antenna. Moreover, the design of a transmitter antenna for DVB-T and T-DAB is presented with Stacked Suspended Plate Antenna (SSPA) structure. Considering the similar products in the world, antennas have been designed in (174-254)MHz for DVB-T and (174-230)MHz for T-DAB with horizontal polarization and return loss ≥ 10 dB. The antenna gives an average gain of 8.5 dB and cross polarization isolation is 31 dB. Contrary to conventional dipole structures, we have employed SSPA structure with two plates for wideband matching and design flexibility. Radiating primary plate has been excited by novel wideband modified inverted L-type probe in a capacitively coupled manner. Vertical plate between primary plate and ground plane also provides wideband matching and adjustment of halfpower beam width properly. Parasitic secondary plate has been used for further matching and tuning. Together with the parametric study of designed antenna, simulation and measurement results for the input impedance, S11, gain and radiation patterns are presented.
  • Thumbnail Image
    ItemOpen Access
    Automatic radar antenna scan analysis in electronic warfare
    (2010) Eravcı, Bahaeddin
    Estimation of the radar antenna scan period and recognition of the antenna scan type is usually performed by human operators in the Electronic Warfare (EW) world. In this thesis, we propose a robust algorithm to automatize these two critical processes. The proposed algorithm consists of two main parts: antenna scan period estimation and antenna scan type classification. The first part of the algorithm involves estimating the period of the signal using a time-domain approach. After this step, the signal is warped to a single vector with predetermined size (N) by resampling the data according to its period. This process ensures that the extracted features are reliable and are solely the result of the different scan types, since the effect of the different periods in the signal is removed. Four different features are extracted from the signal vector with an understanding of the phenomena behind the received signals. These features are used to train naive Bayes classifiers, decision-tree classifiers, artificial neural networks, and support vector machines. We have developed an Antenna Scan Pattern Simulator (ASPS) that simulates the position of the antenna beam with respect to time and generates synthetic data. These classifiers are trained and tested with the synthetic data and are compared by their confusion matrices, correct classification rates, robustness to noise, and computational complexity. The effect of the value of N and different signal-to-noise ratios (SNRs) on correct classification performance is investigated for each classifier. Decision-tree classifier is found to be the most suitable classifier because of its high classification rate, robustness to noise, and computational ease. Real data acquired by ASELSAN Inc. is also used to validate the algorithm. The results of the real data indicate that the algorithm is ready for deployment in the field and is capable of being robust against practical complications.
  • Thumbnail Image
    ItemOpen Access
    Design and analysis of finite arrays of circumferentially oriented printed dipoles on electrically large coated cylinders
    (2004) Güner, Barış
    Conformal antennas and arrays are used in a wide range of applications including mobile communication systems, missiles, aircrafts and spacecrafts. In these applications, the conformality is required for aesthetic and aerodynamic constraints and reducing the radar cross-section. Antennas and arrays conformal to the cylindrical host bodies are particularly important since cylindrical geometry can be used to approximate most of the practical problems and it is a canonical geometry. However, the available design and analysis tools for antennas/arrays conformal to cylindrical host bodies are either approximate methods or restricted to small arrays. Recently, a hybrid method based on Method of Moments (MoM) combined with a Green’s function in space domain is proposed to solve the aforementioned problem. In this work this method is used to analyze finite, phased arrays of circumferentially oriented printed dipoles conformal to the dielectric coated electrically large circular cylinders. The accuracy and efficiency of the method comes from the computation of the appropriate Green’s function which is the kernel of the electric field integral equation to be solved via MoM. There are three different high-frequency based representations for the Green’s function in the spatial domain which are valid in different but overlapping regions: Planar representation, steepest descent path (SDP) representation and the Fourier Series (FS) representation. These different representations are used interchangeably to obtain the most accurate solution that requires the least amount of computational time. Several modifications on the method are made in this work to increase the efficiency and accuracy of the solution. The effects of the array and host body parameters on the performance of the array are presented. The results are compared with a previously published spectral domain solution to show the accuracy of the method. Also, performance comparisons with those of the cylindrical arrays of axially oriented dipoles and planar arrays are made to observe the effects of curvature and the dipole orientation on the performance of the array.
  • Thumbnail Image
    ItemOpen Access
    Design and fabrication of resonant nanoantennas on chalcogenide glasses for nonlinear photonic applications
    (2013) Duman, Hüseyin
    Optical nanoantennas are the metallic nanostructures which confine electromagnetic waves into sub-wavelength volumes at resonant conditions. They are used for various applications including biological and chemical sensing, single molecule spectroscopy, manipulation and generation of light. Combining extremely large electromagnetic field enhancement in plasmonic resonant nanoantenna with high optical nonlinearity of chalcogenide glass leads to a low-threshold broadband light generation scheme in sub-wavelength chip-scale structures. New frequency generation with ultra-low pumping power in plasmonic nanostructures allows compact on-chip light sources which can find applications in single molecule spectroscopy, optical signal processing and broadband lasers. We propose plasmonic nanoantenna chalcogenide glass systems for initiating nonlinear phenomena at low threshold. Size and shape of antennas are optimized according to linear refractive index of substrate and surrounding media for this purpose by finite difference time domain (FDTD) simulations. Resonant behaviour of antennas at their near-field and nonlinear response of optically highly nonlinear chalcogenide glasses are investigated. On resonance, strong field accumulation at the interface of the gold stripe and highly nonlinear As2Se3 glass triggers a start of the spectral broadening of incident beam accompanied by third harmonic generation at an ultra-low threshold power level of 3 W/µm2 . Moreover, we fabricate the designed structures by electron beam lithography, wet chemical techniques and optimize each fabrication step of processes by several experiments. Fabrication steps are explained and SEM images of related steps are presented.
  • Thumbnail Image
    ItemOpen Access
    Development of closed-form Green's functions to investigate apertures on a pec circular cylinder covered with dielectric layer(s)
    (2009) Akyüz, Murat Sencer
    Closed-form Green’s function representations for magnetic sources, which is in general used to represent aperture type antennas on conducting surfaces, are developed for a cylindrically stratified media. The resultant expressions are valid for almost all possible placements of source and observation points including the cases where ρ = ρ 0 and φ = φ 0 . Hence, they can be used in a Method of Moments solution procedure. In the course of obtaining these expressions, the conventional spectral domain Green’s function representations for magnetic sources are reorganized in order to handle relatively large cylinders and the axial line problem. Available acceleration techniques that exist in the literature are implemented to perform the summation over the cylindrical eigenmodes efficiently and to handle some numerical problems along the kz integration path. Then, the resulting expressions are transformed to the spatial domain using the discrete complex image method with the help of the generalized pencil of function method, where a two-level approach is used. It should be noted that a similar methodology has recently been developed for electrical sources and very accurate results have been presented. In this work, its magnetic source counterpart has been developed. Numerical results are presented in two different forms: (a) ρ 6= ρ 0 ; the magnetic source is on the conducting cylinder, which forms the innermost layer of the dielectric coated cylinder. This is a typical scenario for the radiation problem of aperture type antennas. (b) ρ = ρ 0 ; both the magnetic source and the observations points are on the conducting cylinder which forms the innermost layer. There is a singledielectric layer on the top of them. This is a typical scenario for the mutual coupling between aperture type antennas.
  • Thumbnail Image
    ItemOpen Access
    Resonant optical nanoantennas and applications
    (2010) Kılınç, Murat Celal
    Being one of the fundamentals of electrical engineering, an antenna is a metallic shape structured to transmit or receive electromagnetic waves. Thanks to the recent advances in nano fabrication and nano imaging, metallic structures can be defined with sizes smaller to that of visible light, wavelengths of several nanometers. This opens up the possibility of the engineering of antennas working at optical wavelengths. Nanoantennas could be thought of optical wavelength equivalent of common antennas. Today physics, chemistry, material science and biology use optical nanoantennas to control light waves. Optical nanoantennas are tailored for many technological applications that include generation, manipulation and detection of light. The near field enhancement of resonant optical nanoantennas at specific wavelengths is their most promising advantage that attracts technological applications. In this thesis, we study the resonance characteristics of optical nanoantennas and investigate the governing factors by numerical calculations. We also evaluate radiated electric field from the resonating nanoantenna. Finally, we employ the resonant near field enhancement in optical nonlinear generation. The fabrication of nanoantennas with FIB milling is also explored.