In this paper, a novel wideband directional coupler using coplanar waveguide multilayer slot-coupled technique is presented and implemented. The coupler uses two coplanar waveguide lines etched on two layers and coupled through an hexagonal slot etched on the common ground plane located between these layers. Firstly, conformal mapping techniques were used to obtain analytic closed-form expressions for the even- and odd-mode characteristic impedances. Secondly, using this approach, a new design of the directional coupler was performed. Both simulation and experimental results show a good performance in terms of bandwidth.
This paper outlines the trend of signal generation in synthetic aperture radar particularly chirp (linear FM signal) generation using digital approach. A study in fundamental of FM signal and typical analog FM signal generation is highlighted. Various signal generation in SAR using digital techniques is discussed and finally the some of the digital chirp generators are presented.
The electromagnetic rays might be shaded when an obstacle occurs in its way. In this paper, the close analytic expressions determining whether a ray is shaded by boards, elliptic cylinders, elliptic spheres and elliptic cones are presented based on general principle of Geometrical Optics. In optical methods like GTD or UTD in computational electromagnetics which are based on various rays, what studied in this paper with the advantages of analytical measures can be useful to keep the rays valid. Several examples are given as further proof.
Some new parameters in Vivaldi Notch antennas are debated over in this paper. They can be availed for the bandwidth application amelioration. The aforementioned limiting factors comprise two parameters for the radial stub dislocation, one parameter for the stub opening angle, and one parameter for the stub's offset angle. The aforementioned parameters are rectified by means of the optimization algorithm to accomplish a better frequency application. The results obtained in this article will eventually be collated with those of the other similar antennas. The best achieved bandwidth in this article is 17.1 GHz.
In this paper, novel compact broadband dual frequency microstrip antennas are presented and broad-band impedance matching is proposed as a method for improve the matching level of antennas. The first proposed design consists of a rectangular microstrip antenna with a pair of parallel slots loaded close to the radiating edge of the patch and three meandering narrow slots embedded in the antenna surface. The second proposed design consists of a rectangular microstrip antenna with a meandering slits. With the first proposed design a size reduction of 34% and 45% for the two resonant frequencies is obtained respectively. The two frequencies have an operation frequency ratio of 1.30 and 1.25. The theoretical design implementation of compensated compact rectangular microstrip antennas with new configuration Pi-matching networks was presented. A new compensation network consisting of RC Mutator circuit and discrete capacitors are employed at the input of the microstrip antenna operating at 1.5 GHz and 2.5 GHz. The performance parameters of the designed microstrip antenna with and without compensation network were compared. The results show that compensation network can improve the return loss level and the resonant frequency can be controlled in a wide RF band.
The diffraction efficiency (DE) of guided optical waves (GOWs) and the magneto-optic (MO) -3 dB bandwidth are key parameters in MO Bragg cells. To improve the diffraction performance, the MO Stokes interaction between magnetostatic forward volume waves (MSFVWs) and GOWs are studied by use of the coupledmode theory in metal clad yttrium-iron-garnet (YIG) waveguides. Our analysis shows that, by adjusting the spacing of the metal layer from the ferrite surface, (1) the DE can be further increased by 7.32 dB compared with that of the inclined magnetization, but the MO bandwidth will be dropped down to the low level in the optimizing waveguide configuration; (2) when the DE and the MO bandwidth should be considered synthetically, a DE improvement of 3.9 dB with a bandwidth about 560 MHz is achieved corresponding to the large gainbandwidth product. Thus, the YIG waveguide coated with perfect metal layers can be used to improve the performance of MO Bragg cells.
In this paper we have theoretically studied the omnidirectional total reflection frequency range of a multilayered dielectric heterostructures. Three structures of Na3AlF6/Ge multilayer have been studied. The thickness of the two layers of the first and second structure is differing from each other and the third photonic structure is the combination of first and second structures. Using the Transfer Matrix Method (TMM) and the Bloch theorem, the reflectivity of one dimensional periodic structure for TE- and TM-modes at different angles of incidence is calculated. From the analysis it is found that the proposed structure has very wide range of omnidirectional total frequency bands for both polarizations.
A novel broadband design of a printed dipole antenna using PBG (photonic band-gap) structures is proposed and studied in the electromagnetic scattering. The high surface impedance and a frequency gap are used to reduce RCS (radar cross section) across needed frequency range (3.7-4.5 GHz). Because the high surface impedance restrains the surface waves, the obtained results show that RCSis reduced by 15 dB at resonance frequency and radiation characteristics of the antenna at operating frequencies are improved. The method of RCSreduction is suggested, and experimental results are presented.
The high-frequency method for solving the scattering from homogeneous dielectric objects with electrically large size in half space is presented in this paper. In order to consider the scattering fields of the targets in half space, the half-space physical optics method is deduced by introducing the half-space Green's function into the conventional physical optics method (PO). Combined with the graphical-electromagnetic computing method to read the geometry information of all visible facets, the equivalent currents and the reflection coefficients are utilized to account of the homogenous dielectric objects with half-space physical optics method in half space. The numerical results show that this method is efficient and accurate.
In synthetic aperture radar (SAR) processing, autofocus techniques are commonly used to improve SAR image quality by removing its residual phase errors after conventional motion compensation. This paper highlights a SAR autofocus algorithm based on particle swarm optimization (PSO). PSO is a population-based stochastic optimization technique based on the movement of swarms and inspired by social behavior of bird flocking or fish schooling. PSO has been successfully applied in many different application areas due to its robustness and simplicity [1-3]. This paper presents a novel approach to solve the low-frequency high-order polynomial and highfrequency sinusoidal phase errors. The power-to-spreading noise ratio (PSR) and image entropy (IE) are used as the focal quality indicator to search for optimum solution. The algorithm is tested on both simulated two-dimensional point target and real SAR raw data from RADARSAT-1. The results show significant improvement in SAR image focus quality after the distorted SAR signal was compensated by the proposed algorithm.
This work proposes a site attenuation method to calculate the intensity of the field received by a mobile phone on a two-lane highway. To validate the model, radio propagation measurement was carried out through the intercity connection highway of the City of Isparta. The measurement system consisted of live radio base stations transmitting at 900 MHz and 1800 MHz. Downlink signal strength level data were collected by using TEMS test mobile phones, and were analyzed by TEMS Investigation, MapInfo and Google earth. Transmitted power-into-antenna was 14 W for both 900 MHz and 1800 MHz. Both base station sectors are facing towards the same direction having a 14 dBi gain. A proposed approximation was compared with real data. The results indicate that wet white pine trees cause 3 dB to 6 dB extra loss at 1800 MHz and about 1 dB to 3 dB extra loss at 900 MHz. Although 1800 MHz transmitter is 10 m higher, it loses its advantage in signal strength at longer distances.
In this paper, an efficient method to obtain the elements current distribution for a non uniformly spaced array is presented. For a given far field pattern, after sampling the array factor the proposed method uses the least mean square error technique to solve the system ofequations rather than solving the previously published Legendre function method. It's shown that the average side lob level obtained by this proposed method is some 5 dB lower in comparison with the existing Legendre function method ofsolution. Ifthe Legendre function method published in the literature is to be used to solve for the current distribution, in the final part ofthis paper, a criteria on how to choose suitable vectors that would result in a 3 dB lower side lobe level performance will be provided.
Wideband code division multiple access (WCDMA) is an interference-limited system. When the system operates at nearly full capacity, admitting another user may affect the stability of the system. Therefore, proper Call Admission Control (CAC) is crucial and should balance between Quality of Service (QoS) requirements for the new user and also for the existing users and at the same time keep the accepted traffic as high as possible. In this paper, we investigate this tradeoff in the uplink direction using power-based Multi-Cell Admission Control (MC-AC) algorithm. Multimedia services are considered with different QoS requirements. Different traffic scenarios are considered. Simulation results reveal that MC-AC algorithms have many advantages over single cell admission control in terms of overall stability of the system and total system throughput.
MEMS phase shifter has been developed using inductors. The design consists of a CPW line capacitively and inductively loaded by the periodic set of inductors and electrostatic force actuated MEMS switches as capacitors. By applying a single bias voltage on the line, the characteristic impedance can be changed, which in turn changes the phase velocity of the line and creates a true time delay phase shift. The governing equations for the impedance and loss are derived. The ABCD matrix is defined for a unit cell and multi-cell DMTL phase shifter to extract scattering parameters equations. The MEMS switch is actuated by a 39 voltage waveform using a high resistance bias line. Estimated spring constant and switching time is 22 N/m and 3 μs, respectively. The structure is designed for Ka-band frequency range. The acceptable frequency range for the design containing 21 cells is between 26 GHz and 27 GHz and optimum condition occurs at 26.3 GHz. For the whole structure and optimum condition the un actuated position results in a return loss -16 dB and insertion loss of -1.65 dB. The actuated position results in a return loss -12.5 dB and insertion loss of -1.6 dB. The phase shift for the whole structure is 190 degree. The optimum condition can be easily changed by modifying the design parameters. The spacing in the proposed structures is S = 250 μm. The structure is also low loss. The length and the loss per bit with the phase shift of 270◦ are decreased by 37.5 percent and 21 percent respectively.
This paper presents an accurate and robust time-domain electromagnetic model for microwave components of integrated circuits. The time-domain model has been validated on different structures such as metallic waveguides, planer lines and the transition of waveguide-microstrip line under harmonic oscillation excitation. The results obtained from simulation were compared to the experimental test results. The simulation results demonstrated that the approach is suitable to model microwave components of integrated circuits.
Dual-polarized antenna is widely used in communication systems such as ECM and DF systems. In this paper a novel doubleridged horn antenna with dual polarizations is introduced for frequency range of 8-18 GHz. Common double ridged horn antennas have single polarization over the operating frequency. We have used five layers polarizer to provide dual polarizations performance of the double-ridged horn antenna. In order to achieve dual polarizations the strips width, strips spacing and layers distances are optimized. It is worth mentioning that the corresponding VSWR of the antenna during the optimization process should be maintain below a certain value (VSWR<2). Simulation results show that the proposed antenna yields dual polarizations performance and low VSWR over the operating frequency. We have used CST software for antenna simulation which is based on the finite integral technique.
The ground conductivity is the most important factor in the transmitter's coverage area in ground wave propagation. Regarding the day-to-day increase in digital broadcasting, a lower sensitivity of this kind of broadcasting and ability to create single frequency networks, it seems necessary to increase the accuracy of ground conductivity to minimize fading zones. The higher the abovementioned conductivity, the lower the ground wave attenuation. Also in this case, the transmitted wave will tilt less towards the ground to satisfy the boundary conditions in electric conductivity and so-called will enter the earth. In most of the presented papers to determine the field strength, conductivity is considered as known, but it's dependent upon the soil genus, the annual/monsoon precipitation and the heat average. Here it is intended to provide a new method based on Mie algorithm to determine the conductivity based on the difference of Horizontal Electric Dipole near the ground. The previous conductivity measurements included determining it in a point by point manner in a low frequency and determining the conductivity based on the coverage area intensity. The new method holds the two methods advantages together.
Analysis of a frequency agile broadband E-shaped patch antenna (ESPA) symmetrically loaded with tunnel diodes is presented in this paper. The notch parameters such as notch-length, notch-width and position are optimized to achieve the optimum broadband operation of ESPA. Under the optimum conditions of ESPA (bandwidth 32.35%), the performance of the antenna is also analyzed as a function of bias voltage of tunnel diode. It may be mentioned that the proposed antenna can be operated in tunable band that varies from 1055 MHz (bandwidth 42.54%) to 1324 MHz (bandwidth 49.77%) with the bias voltage. Further, the radiated power of the proposed antenna is enhanced by 5.67 dB as compared to the E-shaped patch antenna.
Recently, hyperthermia has been investigated as an alternate therapy for the treatment of tumors. This paper explored the feasibility of preferential hyperthermia as a method of treating deep seated tumors. The overall goal of this research was to determine theoretically if preferential heating could be used to attain the desired thermal dose (DTD) for a two cm diameter tumor. The simulations in this work show that, when using a single rod insert, the model cannot provide enough energy for an entire 2 cm diameter tumor to receive the DTD. However, when using an enhanced design model with multiple (4) rods inserts, the DTD could be attained in a tumor up to 3.5 cm in diameter. This study involved using the model a spherical 2 cm tumor, assuming the tumor is located in deep tissue with a constant perfusion rate and no major blood vessels nearby. This tumor was placed in the center of a cube of healthy tissue. To achieve the preferential heating of the tumor, a rod insert was placed in the center of the tumor and microwave energy was applied to the insert (in the form of volumetric heating). The thermal modeling of this system was based on the Pennes Bioheat equation with a maximum temperature limitation of 80◦C. Additional enhanced design models were also examined. These models include 2 cm and 4 cm tumors with four rod inserts symmetrically placed about the tumor and a 4 cm tumor model using a single rod insert with antennae attached to insert to increase energy distribution to the tumor. The simulations show that only the enhanced design cases with four rods inserts can achieve the DTD for an entire 2 cm tumor. The main purpose of this research was to determine if a minimally invasive treatment system using one or more rod inserts could be used to preferentially heat (and attain the DTD) a 2 cm diameter (or larger) tumor. Achieving the DTD for a 2 cm or larger tumor was important because currently the maximum diameter tumor that can be treated via hyperthermia is approximately 2 cm. In the remainder of this paper. I present the following: First, a background of prior research performed on various subject matters related to basic hyperthermia treatments, combination hyperthermia treatments, and computer modeling. After that, the development and verification of simplified thermal computer models of human tissue is described. Discussed next is the method of calculating the resulting thermal dose, the process of analyzing the results of the simulations of the thermal computer models. Once these introductory topics have been considered, the results of the computer modeling (using the primary thermal model) are presented. First, the effects of varying the perfusion rates in the computer model are explained. Then, a comparison of the overall treatment times, where the optimal treatment time was chosen, is discussed. Presented next is the results of varying the heat input rate. Rates examined include a constant heat generation rate, a constant insert temperature, a pulsed heat generation rate, various ramp heat generation rates, as well as exponential decay heat generation rates.