An effective method for improving the characteristics of the microstrip parallel coupled line coupler is proposed. Some grooves are oriented parallel to the strips and just next to them. It can be shown that an appropriate depth of the grooves can be used for equalizing the even- and odd-mode phase velocity in a coupled microstrip lines with proper geometrical dimensions. Sets of design graphs are derived for various depths of grooves as a parameter and with curves that implies phase velocity equalization curves. The simulated scattering parameters for couplers in conventional and proposed topology show the efficacy of the new grooved substrates.
Cyclic delay diversity (CDD) is a simple approach to increase the frequency selectivity of the channel in an orthogonal frequency division multiplexing (OFDM) based transmission scheme. However, CDD can cause serious degradation in the performance of channel and frequency estimation in the frequency domain. This paper suggests a post-FFT frequency estimation scheme suitable for arbitrary cyclic delays in the CDD-OFDM system. By partitioning uncorrelated pilot subcarriers into subsets to be flat, and performing frequency estimation for each pilot subset, a robust integer frequency offset estimation scheme is derived.
Current driven electrostatic ion cyclotron instability has been studied for parallel flowv elocity shear with perpendicular a.c. electric field to the ambient magnetic field for bi-Maxwellian density drift distribution function. The method adopted for expression for dispersion relation and growth rate is kinetic approach and method of characteristic solution for ionospheric plasma. The effect of a.c. frequency, density gradient, and velocity shear scale length has been discussed.
There are various techniques for the deposition of SiO2 films on silicon. Flame Hydrolysis Deposition (FHD) techniques is the most economical technique for the deposition of SiO2 films. In this technique the SiO2 films are deposited by hydrolysis of SiCl4 in a high temperature H2-O2 flame. In the present study we present the growth of SiO2 films by indigenously developed FHD system and organic compound Tetraethoxyorthosiliate/Tetraethoxysilane TEOS as source of silicon. The films deposited by the FHD system are porous and need annealing at higher temperatures for the densification. We present here for the first time direct dense glassy transparent SiO2 films deposited by our FHD system. The optical properties of the deposited films were studied by ellipsometery. FTIR spectroscopy was carried out to study the various characteristic peaks of SiO2 bonds. The peaks corresponding to Si-O-Si stretching, bending and rocking modes are observed at 1090 cm-1, 812 cm-1 and 463 cm-1 respectively. The absence of peaks corresponding to the OH bond in the deposited film reveals that the deposited films are most suitable for the photonic devices application. The surface analysis was carried out using SEM. The EDAX of the deposited film confirms the composition of the Si and O in the deposited film.
In this paper, a compact design and construction of microstrip Ultra Wide Band (UWB) antenna is proposed. The proposed antenna has the capability ofop erating between 4.1 GHz to 10 GHz. The antenna parameter in frequency domain analysis have been investigated to show its capability as an effective radiating element. Furthermore, time domain Gaussian pulse excitation analysis in UWB systems is also demonstrated in this paper. As a result, the simulation results demonstrated reasonable agreement with the measurement results and good ultra-wideband linear transmission performance has also been achieved in time domain.
This paper presents microstrip transmission lines for designing a microstrip open loop resonator bandpass filter and a novel dual band transmitter. Microstrip open loop resonator bandpass filter with the dumbbell DGS under feed lines enhances the harmonic suppressed at the center frequency of 2.44 GHz. An asymmetric dumbbell DGS-integrated microstrip line is applied to the dual band transmitter which performs as a frequency doubler at 6.8 GHz or a power amplifier at 2.4 GHz. For the proposed bandpass filter,it has a wide stopband characteristic with attenuation -25 dB up to 8 GHz and has an -1.25 dB insertion loss by using two dumbbell DGS. Measurements of the dual band transmitter show that in frequency double mode,fundamen tal suppression and maximum output are -41 dBc and 7.8 dBm. And in amplifier mode,second harmonic suppression,P1 dB and gain achieve -52.6 dBc,13.7 dBm and 16.5 dB, respectively.
Simultaneous multiple beam generation by phased array antennas have great importance in recent time, e.g., multiple access satellite communication systems, MIMO (multiple input and multiple output), target tracking radars etc. Here in this article a novel yet simple wideband multiple beam formation network (BFN) has been proposed. Unlike the conventional phase shifter based system, this scheme is based on true time-delay units which is potential for wideband application.
A semi-analytic method, based on scattering approach is applied to analyze the finite size photonic crystal cavities surrounded by cylindrical dielectric rods.The resonant frequency and the quality factor (Q) are determined by this method.Also, with a source at the center of the cavity, field and energy distribution can be obtained at different frequencies.The algorithm is simple to simulate on PCs. There is no need for absorbing boundary conditions which are required in most numerical methods.Using the symmetry of the structure the computational cost is reduced to 1/8 and 1/12 those of the square and hexagonal lattices respectively.Since the computational time is very low (in the order of one minute) the variation in size and dielectric constant of the rods can be examined easily.It is shown as an example that by varying the radius of the rods according to their distance from the center of the cavity, the Q factor is increased considerably in comparison with that of uniform structures.
A novel design approach for erbium-doped fiber amplifiers is proposed based on particle swarm optimization algorithm. The main six parameters of the EDFAs including: pumping wavelength, input signal power, fiber numerical aperture, erbium-doped area radius, erbium concentration, and the fiber length are optimized utilizing a fast and efficient method called particle swarm optimization algorithm. In this paper, a combination of fiber amplifier bandwidth, gain, and flatness are taken into account as objective function and the results are presented for different pump powers. Our investigation shows that particle swarm optimization algorithm outperforms genetic algorithm in convergence speed, straightforwardness, and coping with highdimensional spaces, when the parameters of EDFA are to be optimized. It has been shown that the required time for the optimization of the fiber amplifier parameters is reduced four times by using particle swarm optimization algorithm, compared to genetic algorithm method.
Maximum likelihood (ML) direction-of-arrival (DOA) estimation is essentially an optimization of multivariable nonlinear cost function. Since the final estimate is highly dependent on the initial estimate, an initialization is critical in nonlinear optimization. Alternating Projection (AP) initialization has been proposed as computationally efficient method for the initialization of the ML DOA cost function. In this paper, we propose a multi-dimensional (M-D) search scheme of uniform exhaustive search and improved exhaustive search. Improved exhaustive search is used to reduce the computational load of uniform exhaustive search. In the improved exhaustive search algorithm, the two-step procedure is applied to reduce the computational load of the uniform exhaustive search initialization scheme. In numerical results, it is shown that the performance of the proposed scheme is better than that of AP initialization.
The design and performance of a circularly polarized microstrip patch antenna, for the application in Wireless Local Area Network (WLAN), are reported here. The antenna is a proximity coupled microstrip patch antenna where the radiating patch is loaded by a V-slot. This miniaturized microstrip antenna has wide bandwidth in the frequency band of WLAN and exhibits circularly polarized far field with very good axial ratio bandwidth. The simulated results using IE3D software are verified by measurement.
A compact printed ultra-wideband (UWB) antenna with band-notched characteristic is presented. The antenna is designed to cover the Federal Communications Commission (FCC) bandwidth for UWB applications (3.1--10.6 GHz) with band-notched at frequency band (5.15--5.825 GHz). The proposed antenna is fed by microstrip line, and it consists of square radiating patch on the top layer with a slotted-parasitic patch on the bottom layer of the antenna. The slotted-parasitic patch acts as a notch filtering element to reject the frequency band (5.15--5.825 GHz) which is used by IEEE 802.11a and HIPERLAN/2. Moreover, the pulse distortions of different input pulses are investigated based on S21 parameters for two cases; face to face and side by side orientations. There is a small acceptable influence on the matching between the input and the output pulses and it is found that the pulse distortion is low. Therefore, the proposed antenna is a good candidate for UWB applications.
A tomography method is proposed to image magnetic anomaly sources buried below a non-flat ground surface, using the expression of the total power associated with a measured magnetic field. It is shown that the total power can be written as a sum of crosscorrelation products between the magnetic field data set and the theoretical expression of the magnetic field generated by a source element of unitary strength. Then, applying Schwarz's inequality, an occurrence probability function is derived for imaging any distribution of magnetic anomaly sources in the subsurface. The tomographic procedure consists in scanning the half-space below the survey area by the unitary source and in computing the occurrence probability function at the nodes of a regular grid within the half-space. The grid values are finally contoured in order to single out the zones with high probability of occurrence of buried magnetic anomaly sources. Synthetic and field examples are discussed to test the resolution power of the proposed tomography.
This paper presents an aperture coupled microstrip antenna with a rectangular patch which is located on top of two slots on the ground plane. The patch and slots are separated by an air gap and a material with low dielectric constant. There is a 50Ω feed line which is divided into two 100Ω feed lines by a two way microstrip power divider under the ground plane. Using a parametric study on the effect of the position and dimensions of the feed line the impedance bandwidth of the antenna (VSWR < 2) is increased to 7.9 GHz (86%) centered at 9.25 GHz and the gain of the structure is more than 7 dB from 5.4 GHz to 8.8 GHz (48%).
The problem of electromagnetic scattering by thin metal plates is formulated in terms of Electric Field Integral Equation and solved by an improved form of the Spectral Iteration Technique. The local solution at the edges of the plate is chosen as initial guess for the unknown surface current in order to guarantee and enhance the convergence of the iterative scheme. Numerical simulations on a square conducting plate are presented to validate the proposed approach.