In this paper a novel numerical optimization technique for antenna configurations is introduced. This algorithm is inspired from colonizing weeds, which is shown to be very robust and adaptive to changes in the environment. Thus, capturing their properties would lead to a powerful optimization algorithm. The feasibility, efficiency and effectiveness of the proposed algorithm for optimization of antenna problems are examined by a set of antenna configurations. The obtained results are compared with a particle swarm optimization technique which is widely used in antenna optimization. Numerical results show that there is a good agreement between the corresponding results.

In this paper, analytical relation for pulse width evolution and broadening in fiber systems using the Volterra series transfer function (VSTF) in linear and nonlinear cases are derived. This evaluation is done for traditional and optimum dispersion compensated fibers. Effects of group velocity dispersion (GVD) and self-phase modulation (SPM) are taken into account. It is shown that the analytical formulation can be applied to design and analysis the long hauls practical systems, and is helpful in understanding the pulse distortion caused by the interaction between SPM and GVD. The proposed relations are extracted analytically and for the first time pulse broadening factor in general case is derived.

Computation of coherent electromagnetic wave propagation through rain medium with a realistic raindrop shape is the subject of this work. T-Matrix approach towards the computation of forward scattering amplitude of raindrops is considered numerically exact. The results of Total Cross Section and forward scattering amplitude due to raindrops with MPP model shape are calculated by T-Matrix method. Both horizontal and vertical polarization of incident wave are considered where specific attenuation, phase shift and cross polarization discrimination (XPD) for terrestrial coherent electromagnetic wave propagation in the frequency range of 3-300 GHz are presented. Furthermore the effect of temperature on specific attenuation vs. frequency is investigated.

This paper presents a new quasi-metallic-wall technique for improving the gain of CB-CPW single antenna and arrays. This technique allows reducing the surface wave losses of the CB-CPW antennas, which decreases the antenna radiation efficiency. It consists on including pins as quasi-metallic wall between the upper and lower ground planes in the CB-CPW antenna structure. To validate the proposed approach, a CB-CPW-slot antenna fed through an inductive coupled CPW-line operating at 5.8 GHz is considered. This approach allows to increase the antenna efficiency from 70% to 95% around the operating frequency. The antenna gain achieves then an improvement of 2 dBi. Also, an antenna array is designed and the pins technique is also applied to prove its applicability for the array case. An efficiency increase from 64% to 95% was achieved. Both single antenna and antenna array withpins were fabricated and measured. A good agreement between numerical and experimental results was obtained.

Various communication systems require single radiating element operating in wide band. In this paper, a novel active integrated single microstrip antenna is proposed and its radiation pattern and gain performance is optimized with analysis. The reactive loading is provided by a negative capacitor section embedded within the patch. The active negative capacitor is made of a field-effect transistor that exhibits negative resistance as well as capacitance. It can, therefore, compensate the loss of an inductor. A microstrip patch operating at 10.5 GHz having 12.2% bandwidth has been utilized as a reference antenna. With the proposed antenna design, the antenna radiation pattern can be as large as about 1.5 times that of an antenna without reactive loading. In addition, it has been shown that active compensation significantly improves the matching level.

A new numerical method is proposed for the analysis of electromagnetic scattering from conducting surfaces. The method involves Monte Carlo integration technique in the Method of Moments solution of the Electric Field Integral Equation for determining the unknown induced current distribution on the surface of the scatterers. The unknown current distribution is represented in terms of a modified entire domain polynomial basis functions satisfying the appropriate edge conditions and symmetry conditions of the problem. This leads to very small order of the Method of Moments matrix as compared to the conventional sub-domain basis functions. The accuracy and the effectiveness of the method are demonstrated in three cases of scattering from conducting circular disks and results are compared with the solutions using conventional sub-domain basis functions. While the sub domain analysis is incapable of handling large domain problems, the proposed method overcomes this limitation. It is also observed that the proposed method is superior to conventional sub-domain method in dealing with singularity problem of the integral equation easily and efficiently.

Desired far-field radiation patterns of 5 × 11 conformal antenna array are synthesized using a hybrid genetic algorithm (HGA), which combines the simplified quadratic interpolation (SQI) method and the real-coded genetic algorithm (RCGA). This hybrid genetic algorithm is shown to outperform standard genetic algorithm (GA) when used to synthesize amplitude weights of the elements to satisfy specified deep notches, nulls and average sidelobe level constraints. The HGA procedure appears to be a high effective means to compensate the mutual coupling effects on the individual element patterns for the conformal antenna array.

Using eigen-modes of a one-dimensional array of slits together with a mode matching technique, we investigate the extraordinary transmission through a subwavelength grating. The analysis serves to determine the contribution of various transmission mechanisms to the overall transmission. It is shown that surface plasmon polaritons excited on the input interface of the grating at certain wavelengths can absorb the incident power and thus reduce the total transmitted power. We also examine the characteristics of the different types of modes involved in the transmission through a metallic grating.

Analytical TM scattering from semi-elliptic channel loaded with confocal elliptic cylindrical impedance core is investigated. Fields in every regions are expressed appropriately in terms of Mathieu functions. Applying boundary conditions at the impedance core and across different regions of channels and using orthogonality of angular Mathieu functions result in two simultaneous set of equations which would be solved numerically.

A novel design of dual circularly polarized antenna is proposed. By etching cross slots on the patch, circular polarization (CP) is achieved. The patch is fed by two L-strips which provide wide impedance bandwidth and high isolation level. Polarization diversity between left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) is provided by switching the two ports and both LHCP and RHCP signals can be received simultaneously. The experimental results show that the 3 dB axial ratio CP bandwidth of the proposed design is increased two times, as compared to a referential CP antenna fed by L-strip. The details of experimental results for the proposed design are presented and discussed.

This paper describes a novel design of a dual-polarized ultra wideband horn antenna. Based on a VSWR ≤ 2.6, the bandwidth of the designed UWB horn antenna is from 8-18 GHz, most suitable for radar systems. A newcoaxial line to quadruple-ridged waveguide transition and a newtec hnique for tapering the flared section of the horn is introduced to improve the return loss and matching of the impedance, respectively. Results of simulation for VSWR, isolation, gain and radiation pattern of designed horn antenna are presented and discussed.

A tiny metallic cylinder placed into a planar dielectric waveguide scatters the field developed by a current-carrying skew strip centralized at the middle of the slab. Due to the small size of the scatterer, the induced surface current is taken independent of the azimuthal angle. The Green's function of the problem is expressed in closed form and it is inserted to the scattering integral after the polar equation of the strip has been determined. The behavior of nearfield quantities in the slab, with respect to geometrical and material parameters, is observed and examined.

Maxwell's equations are solved to determine transient electromagnetic fields inside as well as outside of a large conducting plate of an arbitrary thickness. The plate is carrying a uniformly distributed excitation winding on its surfaces. Transient fields are produced due to sudden application of a d.c. voltage at the terminals of the excitation winding. On the basis of a linear treatment of this initial value problem it is concluded that the transient fields may decay at a faster rate for conducting plates with smaller values of relaxation time. It is also shown that the growth of flux in a perfectly nonconducting plate is a piecewise linear function of time and the current in its excitation winding is a series of stepfunction of time.

Abstract-In this paper, we present a novel improved hairpinline microstrip narrowband bandpass filter with via ground holes. The new filter design methodology is derived from conventional hairpinline filter design. This design methodology incorporates use of λ/8 resonators, thereby reducing the size of the filter by 35% as compared to the conventional design. An analysis is presented to show the effects of tap point height and microstrip width on fundamental parameters of filter and subsequent relationships are developed. Through use of via ground holes and a wider microstrip line for resonators, 3 dB Fractional Bandwidth (FBW) less than 2%, Insertion Loss (IL) less than 1.6 dB and Return Loss (RL) better than 40 dB is achieved with midband center frequency 1 GHz. Spurious response suppression is achieved till 3ƒ₀. Robustness of this design approach is demonstrated by designing filters on two more substrates having ε_r 2.17 and 9.2. As low as 0.48% FBW was achieved by using different substrates. The design approach is successfully tested for center frequency upto 2 GHz beyond which folding the resonator becomes practically difficult. Finally, a bandpass filter is designed with this design methodology and fabricated using FR4 substrate. S-parameter measurements show a good agreement with the simulated results.

In this research, an integro-differential equation which describes the charged particle motion for certain configurations of oscillating magnetic fields is considered.The homotopy perturbation method (HPM) is used for solving this equation.HPM is an analytical procedure for finding the solutions of problems which is based on the constructing a homotopy with an imbedding parameter p that is considered as a small parameter.The results of applying this procedure to the integro-differential equation with time-periodic coefficients show the high accuracy, simplicity and efficiency of this method.

This paper presents a theoretical investigation on the pulse preserving capabilities of the CPW-fed circular disk monopole antennas at the assistance of correlation factors. The distortions of the radiated signals, which are mainly caused by the bandwidth mismatch between the antennas and the source pulse, are alleviated by using suitable source pulse. The ringing and pulse-width spreading of the radiated signals caused by the energy-storage effects of the dielectric substrate are discussed in detail. Possible improvement solutions and an example are provided. The improvement of the correlation factors introduced by selecting suitable substrate parameters is about 7% on an average. With the physical insight and design example, the proposed solutions are expected to find applications in the design of printed UWB monopole antennas for better pulse preserving capabilities.

We propose an integral-equation formulation for analyzing EM field of 2-D dielectric waveguide devices. The complex 2-D device is first divided into slices of 1-D horizontally layered structures. The entire EM solutions are determined by transverse field functions on the interfaces between slices. These functions are governed by a system of integral equations whose kernels are constructed from layer modes of each slice. These unknown tangential field functions are expanded as some linear combination of known basis functions. Various waveguide devices such as multi-mode interferometers, waveguide crossing and quasi-adiabatic tapered waveguides can be formulated and studied using present formulation.

A novel miniaturized circularly-polarized antenna is presented. By using tapered meander-line structure, the designed antenna has a size reduction rate of 96% compared with a traditional turnstile dipole antenna. The unequal lengths of the two meanderline dipoles are properly adjusted to achieve a circularly polarized radiation. Furthermore, the impedance matching is effectively realized by a lumped matching network. A prototype of the antenna with a size of 64 × 64mm² has been implemented and tested. Good agreement is achieved between the simulated results and the measured results, which shows that the axial ratio is less than 3.0 dB and the VSWR less than 2.0:1 in the frequency range of 450 ± 1.5 MHz.

In this paper we have investigated optical pulse propagation in a dense dispersion managed (DM) optical communication system operating at a speed of 100 Gb/s and more taking into account of the effects of third order dispersion, intra-pulse Raman scattering and self steepening. Using perturbed variational formulation, we have obtained several ordinary differential equations for various pulse parameters. These equations have been solved numerically to identify launching criteria in the first DM cell of the system. Full numerical simulation of the nonlinear Schr¨odinger equation has been employed to identify effects of higher order terms on pulse propagation and to investigate the intra-pulse interaction. The roles played by these higher order linear and nonlinear effects have been identified. It has been found that the shift of the pulse centre due to intra-pulse Raman scattering increases with the increase in the distance of propagation and average dispersion. We have noticed that for higher value of average dispersion pulses travel less distance before collision than for lower average dispersion.

An analytical formulation based on physical optics is employed to determine the field and the radiated power distribution by open-ended circular waveguides. Using the incomplete Hankel functions, the line integrals yielding the electromagnetic field are evaluated in closed analytical form along the waveguide axis. It is shown that cylindrical waves are generated by the surface currents flowing on the waveguide walls, while spherical waves are produced by the currents and charges excited at the waveguide truncation. Cylindrical and spherical waves are shown to be responsible for the field synthesis in terms of waveguide modes and scattered fields at the waveguide mouth. Numerical results concerning the spatial distribution of the electromagnetic field and associated power density are compared with previously published results, showing the advantage of the incomplete Hankel functions formulation. Finally, the uniform asymptotic representation of the incomplete Hankel function is shown to be suitable to compute the field distribution on the waveguide axis except for the TE₁1 and TM₀₁ modes.