Agah Oktay Ertay

Design and simulation study of Helix Traveling Wave Amplifier for Ku-Band applications

The purpose of this investigation is to present a Ku-Band Helix Traveling Wave Tube Amplifier (TWTA) design and simulation procedure with considering initial design assumptions. The design process which consists of four critical steps is stated. Firstly, required input parameters such as dc beam current (Io), dc beam voltage (Vo) and frequency band of operation are chosen. Determination of the design objectives such as gain and output power constitutes the second stage of the design procedure. For this purpose, overall gain in considered frequency range is specified as over 20 dB. The output power is aimed to 100 W. To obtain design objectives mentioned in the second step, it is necessary to have optimum helix slow wave structure (SWS) design parameters such as helix pitch, radius and pitch angle. Therefore, the optimized design parameters of the SWS are determined by using Eigen Mode Solver (EMS) (cold (beam absent) analysis) of Computer Simulation Technology (CST) Microwave Studio (MWS) for acquiring the beam-wave synchronization. Particle in Cell (PIC) simulation (hot (beam present) analysis) is carried out by assuming the uniform electron beam flow. The length of the interaction structure of the designed TWT is nearly 110 mm and all design objectives are nearly achieved as it is expected. Many crucial figures related to gain, power and beam wave interaction are depicted with detailed explanations. Furthermore, the design limitations of this proposed design due to assumptions are also clarified.

On the assessment study of small signal gain analysis of helix type traveling wave tube with pierce parameters

The main idea of this study is to investigate the small signal gain analysis of the helix type Traveling Wave Tubes (TWTs). Dispersion equation of the TWT is discussed and the behavior of propagation constants of the helix TWT structure is expressed when beam-wave interaction occurs. All possible waves or modes which play important role in the amplification process are considered. The effects of loss due to interaction circuit, space charge effects and beam velocity variations are taken into account when solution of the dispersion equation and TWT gain characteristics are carried out. Fundamental aspects of the TWT small signal gain analysis with Pierce parameters such as b (velocity parameter), QC (space charge parameter), d (cold tube circuit loss) are examined. Some significant figures are obtained to express the behavior of the gain with respect to Pierce parameters. It is noted that Pierce small signal theory gives important information to investigate the gain characterization of the TWT considering natural effects of beam velocity, circuit loss and beam-wave interaction.

On the study of comparative analysis of dielectric loaded effects for rectangular cavity resonators

In this paper, a comparison study of dielectric loaded effects of rectangular resonant cavity in terms of resonance frequency, dielectric loading rate and various dielectric constant for different TEy and TMy modes is presented. This study includes two stage analysis procedures. Firstly, field expressions and resonance frequency of the dielectric loaded rectangular resonant cavity with respect to dielectric loading rate are obtained for different TEy and TMy modes by using semi-analytical approach. Secondly, perturbation method is applied for acquiring resonance frequency of each chosen different mode and dielectric constant with respect to dielectric loading rate. Comparison of two different method in terms of variation of resonant frequency with respect to relative dielectric thickness is performed for different dielectric loading case for the same mode and different modes for the same dielectric loading. The results show that perturbation approach can be good alternative to semi-analytical method to calculate the variation of the resonant frequency with respect to relative dielectric thickness.

A compact bandstop filter design for X-band applications

The main objective of this work is to present a compact microstrip bandstop filter for X-band applications. The designed filter covers X-band and has stopband bandwidth with better than 2.5GHz for -20dB. Maximum |S11| value in the passband region is below -15dB for the final filter. Optimum distributed bandstop filter design method is used to acquire the design goals. The final filter has a compact size with 12.87mm × 7.04mm. Two-stage design procedure is proposed to realize design objectives. It is proposed in the first stage of the design procedure to have realizable open stubs which is difficult to implement for given dielectric substrate properties. To remedy this difficulty, a wide stopband region is selected. The second stage of the design procedure presents an optimization process to achieve desired filter. In order to examine the frequency responses of all design steps, three commercial electromagnetic simulators are used. Consistent simulation results are obtained before implementation.

A coplanar vivaldi antenna design with improved frequency response for microwave breast imaging

The main goal of this work is to present a planar director added coplanar Vivaldi antenna with improved impedance bandwidth, directivity for microwave breast imaging applications. Three stage design procedure is proposed to enhance the directivity and impedance bandwidth. Proposed antenna operates from 1.3GHz to 7.09GHz which fractional bandwidth is over 138%. The directivity of the proposed antenna is relatively enhanced at higher frequencies. The designed antenna structure has 64×70×1.6 mm3 dimensions and suitable for microwave imaging applications.

Investigation of schizophrenic EEG signals using wavelet transform functions

The aim of the present study is to investigate EEG data of schizophrenic patients and healthy individuals using different wavelet transform functions and to utilize those functions as a tool for revealing the brain locus causing schizophrenia. In this study, pretreatment of EEG data of both schizophrenic patients and healthy controls were performed to eliminate artifacts and the data were filtered with a 40 Hz low pass filter. Filtered data were subjected to continuous wavelet transform in order to obtain wavelet coefficients as much points as in EEG signal in a range of 0-256 scale. Scales for different EEG bands ( e.g. delta <; 4Hz) were determined. For each channel standard deviation and mean values of coefficients for delta, theta, alpha, gamma bands and the results for patients and healthy individuals were compared to find out the brain locus the disease is originated from. Same process was performed with different wavelet transform functions, and the results were compared.

A compact CPW-fed wide band microstrip antenna design for mobile applications

In this work, a CPW-fed wide band antenna, , covering mobile applications is presented. The proposed antenna operates between 1600 - 2550MHz and has a gain of 2dBi. A relatively small design is implemented for various wireles communication applications such as wireless local area networks(WLANs), 3G. The designed antenna has matched impedance and dipole like radiation pattern. The proposed antenna has a very stable radiation patern in frequencies of operation.

A wideband CPW-fed microstrip antenna design for wireless communication applications

In this study, a wideband linear polarized microstrip antenna by co-planar waveguide fed with three resonant is presented. Antenna has square slot and fork shaped geometry. This microstrip antenna covers wireless communication systems such as wireless local area networks, global positioning systems, digital communication systems, personal communication systems as well as it has 2750 MHz bandwidth and 2415 MHz center frequency of operation. The antenna is designed with its optimal parameters that can cover wireless communication systems.

A compact low pass filter design with a fan-shaped defected ground structure for broad stopband

The aim of the paper is to acquire low pass filter with broad stopband frequency characteristics. To achieve this, a novel fan-shaped defected ground structure (DGS) is presented and compared with other conventional simple DGS units such as square, circular and elliptical. Furthermore, effects of slot length variation of the novel DGS unit are analyzed. Finally, top side of the structure is modified adding several impedance lines to the center of the microstrip line to obtain broad stopband. Designed filter is quite compact with a dimension of 20 mm × 14 mm × 1.27mm. Simulations of design procedure are achieved with ANSYS HFSS and SONNET.