Serkan Simsek

A planar ultra-wideband monopole antenna with half-circular parasitic patches

A simple planar ultra-wideband (UWB) microstrip-fed antenna with defected ground structure and two parasitic patches is presented. Two symmetrical quarter-circle shaped segments are cut both on the each of lower edges of the radiating patch and on the each of upper edges of the ground plane. These segments provide a wider bandwidth than the ordinary rectangular antenna especially in the middle frequencies. By means of removing U-shaped slot in the radiating patch the radiation characteristics of the 7-10 GHz frequency range are improved. Two half-circle shaped parasitic patches are connected via a hole to the ground plane. These patches are added on both sides of the 50-Ω microstrip-fed line to achieve good radiation performance for frequencies higher than 10 GHz. The proposed antenna is simulated by ANSYSs HFSS program using finite element method (FEM). The simulation results show that 127% of the impedance bandwidth is between 3.1 and 13.8 GHz for 20log|S11|<;-10 dB. The simulated antenna is fabricated on FR4 substrate and measured.

A simple and compact CPW-fed UWB printed monopole antenna with defected ground structures

A planar simple and compact monopole antenna for UWB applications is proposed with CPW feeding. The radiating patch of the antenna consists of a top-cut half-circle together with a triangle on the lower edge. The bottom side of the antenna includes a rectangular defected ground plane with two different symmetrical bevels. By cutting out these bevels on the ground plane, bandwidth coverage of the overall UWB range except 5.4-7 GHz frequency band is provided. To enhance input impedance bandwidth characteristics at 5.4-7 GHz frequency band, dimensions of the triangular part on the lower edge of the patch and top-cut half-circle part on the upper edge are optimized. The overall size of the proposed antenna is 22×20×1 mm3. Simulations are carried out using commercially available ANSYSs HFSS program which uses the finite element method (FEM). Results show that 110% of the impedance bandwidth between 3.6 and 12.2 GHz for VSWR<;2 is achieved. Moreover, antenna has a stable omnidirectional pattern at XZ plane over the frequency band. Also, the presented antenna is fabricated on FR4 substrate and it is measured.

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 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 monopole antenna with enhanced bandwidth by using slots and parasitic strips

A novel compact ultrawideband (UWB) microstrip monopole antenna with enhanced bandwidth by use of slots and parasitic strips is presented. The proposed antenna consists of a semicircular shaped patch with a U-slot and two rectangular slots, a semi ellipse shaped ground plane, and two parasitic radial strips. The designed antenna has a small size of 20 × 22 × 0.8 mm3 and operates over the frequency band between 3.76 and 11.84 GHz for 20log |S11| <; -10dB.

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.

Small printed UWB monopole antenna

A compact microstrip-fed ultra-wideband monopole antenna is presented. The antenna has a simple planar structure and occupies a compact size of 22 mm × 16 mm × 1 mm, including the feeding mechanism. Proposed antenna, which is printed on FR4 substrate with a relative permittivity of 4.4 has been easily fabricated and has low manufacturing cost, has a bandwidth from 3.8 GHz to 12 GHz, and has a stable omni directional pattern at x-z plane over the frequency band. In antenna design, we simulate and investigate this antenna structure by using finite element method (FEM) based Ansofts HFSS program.