Nursel Akcam

Estimation of Radar Cross-Section in Rayleigh, MIE, and Optical Regions by the 2-D-FDTD Simulation

In this paper, the far-field electromagnetic fields were calculated by using near-field/far-field (NF/FF) transformation technique from the near field finite-difference time domain (FDTD) data obtained by total field/scattering field (TF/SF) formulation. To evaluate the effectiveness of scattering mechanisms depending on the frequency used, the target geometry and the electrical properties, first of all simple shapes such as a square cylinder, a circular cylinder, and an equilateral triangle, were studied. It has been shown that the radar cross section (RCS) calculations can be done in Rayleigh, Mie, and optical regions by the 2-D FDTD simulation. Finally, the RCS behavior of an aircraft model composed of simple shapes as ellipse and triangle are investigated for different illuminations and different frequencies.

Array Antenna Using Defected Ground Structure Shaped With Fractal Form Generated by Apollonius Circle

A novel multiband antenna was designed and manufactured by blending a fractal shape and defected ground structure achieving superior performances yet within a slight architecture that makes this design a perfect fit for geostationary satellite communications. Apollonius circles were utilized in order to design a sui generis fractal shape that was etched on the ground face of the antenna to tune different frequency bands. The designed single antennas are aligned to build

Collaborative Intent Exchange Based Flight Management System with Airborne Collision Avoidance for UAS

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Analysis of apollonius circles fractals as frequency selective surface

array antenna structure. The test results of the manufactured antenna were both aligned successfully with computer simulations and proved the efficiency of this very small antenna design.

Heterogenous Computing on Iris Matching with OpenCL

This paper presents a Flight Management System (FMS) with multi-level autonomy modes that meet the requirements of future flight operations for unmanned aerial systems (UAS). It is envisioned that the future of airspace will become highly heterogeneous and integrate non-standardized aerial systems. In that case, only ground systems will be able to predict future trajectories based on performance models (stored in huge parametric databases). Meanwhile, airborne systems are required to share information. The proposed FMS structure integrates new functionalities such as (1) formal intent and information exchange and collaboration in tactical planning utilizing air-to-air and air-to-ground data links and (2) decentralized, short-term collision detection and avoidance. The air-to-ground data link enables intent sharing and allows field operators (i.e., flight operators or air traffic controllers) to interpret, modify, or re-plan UAS flight intent. The onboard FMS persistently monitors the airspace, tracks potential collisions with the other aircraft and the terrain, and requests re-planning when it detects a possible issue. When an immediate response is needed, the onboard FMS generates a 3D evasive maneuver and executes it autonomously. Flight traffic information is obtained from ADS-B/In transponders and air-to-air data links. ADS-B-In/Out implementations make the unmanned systems more visible to the systems in 3D. In addition, the air-to-air data links enable intent sharing between airborne systems and are traceable in four dimensions (i.e., space and time). The experimental FMS was deployed in quadrotor UASs and a ground station and GUI was designed to perform demonstrations and field experiments for the issues introduced in the paper.

Secure communication tests carried out with next generation narrow band terminal in satellite and local area networks

In this study, the response of a recently proposed fractal structure namely Apollonius Circles to an incident plane wave is addressed in terms of resonance frequencies, bandwidth and stability at oblique incidence. Although the base structure has been applied as a defected ground plane, the stand alone reflection characteristics is still needed to be examined. 0–30 GHz range is examined in both TE and TM modes and the applicability of the unit cell structure as an FSS is discussed.

Field leakage reduction using a two-dimensional matched numerical dispersion method and high-order cubic curvilinear interpolation [em programmer's notebook]

This study presents parallelization of Hamming Distance algorithm, which is used for iris comparison on iris recognition systems, for heterogeneous systems that can be included Central Processing Units (CPUs), Graphics Processing Units (GPUs), Digital Signal Processing (DSP) boards, Field Programmable Gate Array (FPGA) and some other mobile platforms with OpenCL. OpenCL allows to run same code on CPUs, GPUs, FPGAs and DSP boards. Heterogeneous computing refers to systems include different kind of devices (CPUs, GPUs, FPGAs and other accelerators). Heterogeneous computing gains performance or reduces power for suitable algorithms on these OpenCL supported devices. In this study, Hamming Distance algorithm has been coded with C++ as a sequential code and has been parallelized a designated method by us with OpenCL. Our OpenCL code has been executed on Nvidia GT430 GPU and Intel Xeon 5650 processor. The OpenCL code implementation demonstrates that speed up to 87 times with parallelization. Also our study differs from other studies, which accelerate iris matching, with regard to ensure heterogeneous computing by using OpenCL.

Spillover Losses in Small Cassegrain Antennas

Communication becomes more and more important day by day and especially secure communication from one end to the other holds a vital place in our daily life. Developed countries which are aware of this fact has started to carry out serious studies on secure communication from one end to the other. One of the most important studies is the project which appeared as FNBDT (Future Narrow Band Digital Terminal) at first and was renamed as SCIP (Secure Communication Interoperability Protocol) later on. FNBDT (Future Narrow Band Digital Terminal) or SCIP (Secure Communication Interoperability Protocol) is a communication protocol which is a result of secure communication need of diferent network devices in contact with each other. The main purpose of the protocol is to provide the new generation terminals which are source of transmission with secure communication with each other through different networks using narrow band. National and international studies on FNBDTISCIP has focused on three main points; FNBDT protocol, SCIP protocol and codes of MELP (Mixed Excitation Linear Prediction) Studies about implementation of FNBDTISCIP are much fewer than theoretical studies on the matter. Some tests of FNBDTISCIP on satellite and local Networks are carried out to overcome this lack of implementation. It is aimed to set up calls on diferent Networks, to check transmission of voice and data with and without any loss and to find out the limits with these tests. Results of these tests were declared before. In this study, some tests on satellite and local Networks are carried out; as a result, values about call set ups and limits of voice and data transmission are compared with ITU (International Telecommunications Union) standards.

SHIELDING EFFECT ANALYSIS OF PATCH ELEMENTS HAVING DIFFERENT NUMBERS AND LENGHTS

In this study, the Total Field/Scattered Field (TF/SF) formulation, one of the methods used for effectively introducing far-field sources into the Finite-Difference Time-Domain (FDTD) Method, is described in detail. The incident fields required for the implementation of the TF/SF formulation were obtained by the Incident Field Array (IFA) Method. The errors introduced in the Incident Field Array Method were presented by numerical examples, and the Matched Numerical Dispersion (MND) Method was applied to a two-dimensional FDTD grid. It was also shown that for wideband pulse excitations, applying the Matched Numerical Dispersion Method to the TF/SF wave source reduced the field leakages nearly 200 dB (subject to double-precision implementation) compared to the Single-Frequency Compensation method for angles of incidence φ = 45. However, a similar improvement could not be obtained for an angle of incidence of φ =30. It was demonstrated that by using higher-order cubic curvilinear interpolation instead of the linear interpolation used in the Incident Field Array Method, the field leakage could be approximately reduced by 70 dB for an angle of incidence of φ = 45 . This higher-order interpolation technique is applicable for any time-dependent plane wave. A 1 GHz sinusoidal wave was used as the incident wave in the simulation.