In this paper, we investigate nonuniformly spaced linear arrays (NUSLA) rigorously. Several important problems in NUSLA design are solved with the combination of the Genetic Algorithm and Conjugate Gradient method (GA-CG). The pattern synthesis for the specified beamwidth and minimum achievable sidelobe level (SLL) are performed and for the first time, the graphs which show the relation between the beamwidth, sidelobe level and number of elements for NUSLA are derived. Also, the NUSLA's pattern for the specified directivity and sidelobe level is synthesized. The graphs showing the behavior of NUSLA relative to the increase of its length for a fixed number of elements are derived. These graphs showthe relations between the directivity and sidelobe level of NUSLA with its length. As a practical design, an array of parallel dipoles is designed for specified beamwidth/sidelobe level or specified directivity/sidelobe level. Furthermore, a novel Neural Network based model for the NUSLA is presented for the rapid and accurate computation of Sparameters. The computed S-parameters are used for the computation of coupling among elements. Then the GA-CG method can adjust these values in the synthesis process to achieve desired pattern and bearable coupling among elements.
This paper proposes the application of the Wiener filter in an adaptive manner in speech enhancement. The proposed adaptive Wiener filter depends on the adaptation of the filter transfer function from sample to sample based on the speech signal statistics (mean and variance). The adaptive Wiener filter is implemented in time domain rather than in frequency domain to accommodate for the varying nature of the speech signal. The proposed method is compared to the traditional Wiener filter and the spectral subtraction methods and the results reveal its superiority.
A new numerical method is presented for the design and optimization of linear arrays of nonuniformly spaced longitudinal slots on the broad wall of rectangular waveguides, based on the Method of Least Squares (MLS). Elliott's design theory for travelling-wave-fed slot arrays is extended to nonuniformly spaced slots. As a common approach in MLS, an error function is formulated according to the design goals (namely the input impedance matching and pattern synthesis) and then minimized with respect to the design parameters (namely slot lengths, offsets, spacings and excitations). Having the slot parameters, one can design a linear slot array which accounts for the desired input impedance matching and array pattern. This approach has the advantage of combining the ``nonuniform pattern synthesis'', which includes the external mutual coupling and element pattern of slots, with ``impedance matching'' and ``calculation of the array parameters''. This procedure increases the design speed as well as synthesizing any desired pattern. The MLS design results and those obtained by HFSS simulation software are in good agreement and verify the accuracy of the proposed method.
This paper presents a new approach for solving accurate approximate analytical solution for strong nonlinear oscillators. The new algorithm offers a promising approach by Hamiltonian for the nonlinear oscillator. We find that these attained solutions are not only with high degree of accuracy, but also uniformly valid in the whole solution domain.
On the base of conductor-backed coplanar waveguide (CBCPW) structure, a novel CB-CPW structure is proposed and analyzed, which is realized by using the UC-PBG structure to replace the back conductor of CB-CPW. From 1.3 GHz to 2.8 GHz, The transmission characteristic of the proposed CB-CPW is better than that of CBCPW, and is similar to that of CPW, therefore, this novel CB-CPW not only owns the advantage of CB-CPW, such as good mechanical strength and good heat yield, but also owns the advantage of CPW, such as good transmission characteristic. At last, a dual-band antenna based on this novel CB-CPW is designed and computed, the numerical results validate that this novel CB-CPW is feasible in microwave application.
A band pass filter with a linearly periodic refractive index profile is discussed in analogy with Kroning Penney model in band theory of solids. The suggested filter is a one-dimensional ternary periodic structure and provides better control in dispersion relation as compared to a binary structure because it has two more controlling parameters relative to those of the binary one. Since three layers are involved in the formation of band gaps a much broader range of dispersion control is obtained. Both refractive index modulation and optical thickness modulation are considered. A mathematical analysis is presented to predict allowed and forbidden bands of wavelength with variation of angle of incidence. It is also possible to get desired ranges of the electromagnetic spectrum filtered with this structure by manipulating the value of the lattice parameters.
The discrete complex image method is one of the most prominent techniques that handle the Sommerfeld integrals encountered in the integral equation formulations of multilayered media. The extraction of surface waves extends the validity of the method to the far field. These surface waves are expressed in terms of Hankel functions that suffers a singularity problem at the origin which contaminates the results in the near field. In this work,w e use a formulation developed recently by the author to derive a new expression for the surface waves. The new expression is shown to obviate the singularity of the Hankel functions at the origin,and hence leads to accurate results in the near field.
The characteristics of radiating longitudinal slots in a rectangular waveguide have been studied. A moment method solution is used with entire basis expansion and testing functions (Galerkin) including the effect of wall thickness. It is shown in this paper. 1) The determination of different parameters like VSWR, reflection coefficients and insertion loss are calculated with the results of normalize reactance and conductance. 2) The Taylor distribution approach with specific SLL for desired linear aperture array antenna. The resonant conductance or resistances are calculated from desired amplitude distribution. The formulation uses transmission matrix approach. The computed result shows excellent agreement with measured results. CST Microwave studio is used for the simulation and is totally based on FIT techniques.
A novel compact dual-band electromagnetic band-gap (EBG) structure is proposed in this paper. The major contribution to this dual-band design is using cascaded mushroom-like units which operate at different frequencies. The position of via is moved off the center of the metal patch to get a lower resonant frequency and the effects of the radius of via are considered at the same time. The method of suspended microstrip is utilized to measure the band-gap characteristics of the EBG structures. Several dual-band EBG structures are designed and compared. Results show that this novel cascaded structure offers additional flexibility in controlling the frequencies of the stopband over a wide range. The cascaded dualband EBG structure has potential application to dual-band antenna and circuit.
The third generation promises increased bandwidth up to 384 Kbits/s for wide area coverage up to 2Mbits/s for local area coverage. A smart antenna technique has been developed specifically to meet the bandwidth needs of 3G [5, 7, 12, 14]. Smart beamforming provides increased data throughput for mobile high speed data application. Here in this paper we worked on MVDR Beamforming scheme for continuing demand for increased bandwidth & better quality of services. Adaptive minimum variance beamforming can be easily implemented to increase capacity as well as suppressing co-channel interference & to enhance the immunity to fading. The computer simulation carried out in MATLAB platform shows the signal processing technique optimally combines the components in such a way that it maximizes array gain in the desired direction simultaneously minimize it in the direction of interference [1, 3, 15, 16].
An open resonance cell (ORC) with finite-length cylindrical mirrors is suggested for making absolute measurements of complex permittivity in the case of stretched cylindrical specimens or liquid dielectrics in cylindrical containers. For H-polarization, we report ORC features simulated in rigorous electromagnetic terms using a twodimensional (2-D) model of an open resonator with cylindrical mirrors and a dielectric test rod inserted. On this basis, the ORC laboratory prototype with finite-length mirrors was built. The measurements of dielectric test rods were performed in the 10 mm wave band. In the studies of dielectric materials, E-polarized modes of the cylindricalmirror ORC demonstrate some specific features, which are discussed, too
The recurrence dispersion equation of coupled single-mode waveguides is modified by eliminating redundant singularities from the dispersion function. A recurrence zero-bracketing (RZB) technique is proposed in which the zeros of the dispersion function at one recurrence step bracket those of the next recurrence step. Numerical examples verify the utility of the RZB technique in computing the roots of the dispersion equation of the TE and TM modes of both uniform and non-uniform arrays.
This paper deals with Approximate Analytical Solutions to nonlinear oscillations of a conservative, non-natural, single-degreeof- freedom system with odd nonlinearity. By extending the Variational approach proposed by He, we established approximate analytical formulas for the period and periodic solution.To illustrate the applicability and accuracy of the method, two examples are presented: (i) the motion of a rigid rod rocking back and forth on the circular surface without slipping, and (ii) Cubic-Quintic Duffing Oscillators. Comparison of the result which is obtained by this method with the obtained result by the Exact solution reveals that the He's Variational approach is very effective and convenient and can be easily extended to other nonlinear systems and can therefore be found widely applicable in engineering and other sciences.
Abstract-In this paper, a novel ultra-wideband switched-beam antenna system based on 4×4 two-layer Butler matrix is presented and implemented to be used in hostile environment, such as underground mines. This matrix is based on the combination of a broadband twolayer slot-coupled directional coupler and a multilayer slot-coupled microstrip transition. With this configuration, the proposed matrix was designed without using any crossovers as used in conventional Butler matrices. Moreover, this new structure is compact and offers an ultra-wide bandwidth of 6 GHz. To examine the performance of the proposed matrix, experimental prototypes of the multilayer microstrip transition and the Butler matrix were fabricated and measured. Furthermore, a three 4-antenna arrays were also designed, fabricated and then connected to the matrix to form a beamforming antenna system at 3, 5.8 and 6 GHz. As a result, four orthogonal beams are produced in the band 3-9 GHz. This matrix is suitable for ultrawideband communication systems in confined areas.
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