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.

In this paper, the previously introduced fuzzy modeling method is used to model the input impedance of two coupled dipole antennas in the echelon form. The initial data of two coupled dipole antennas in the parallel and collinear form, which are required for the model, are obtained using the MoM (Method of Moments). Then, the knowledge of two coupled dipole antennas in the echelon form is easily predicted based on the knowledge of two coupled dipole antennas in the parallel and collinear form and the concept of spatial membership functions. Comparing the results of the proposed model with MoM shows an excellent agreement with a vanishingly short execution time comparing with MoM.

A portable ultra wide band radio direction finder has been constructed based on the principle of stereophonic direction recognition of sound by human ears. The instrument consists of two log periodic antennas having identical electrical properties. They are positioned in a plane, preferably parallel to the ground. The directivities of the antennas are aligned at slightly different directions with respect to each other. Their output powers are compared at the source frequency for the respective polarizations. The back lobes of the antennas have been reduced by symmetrically positioning two metallic plates (reflectors) behind the antennas. The antennas, reflectors and a compass are mounted over a video camera stand such that they could be manually positioned in the azimuth. Since the antennas are of identical make, ideally the radiation pattern of either antennareflector combination should behave as a flipped image of the other set. For any particular polarization and frequency, the outputs from the antennas are compared with each other. The antenna assembly is rotated between 0 and 360^◦ in the azimuth until the power difference gets minimized. This position relates to the direction of the source and is indicated on the compass, provided there exits a single radio source at that frequency.

This paper presents a thorough study of the time-domain theory of metal cavity resonators. The completeness of the vector modal functions of a perfectly conducting metal cavity is first proved by symmetric operator theory, and analytic solution for the field distribution inside the cavity excited by an arbitrary source is then obtained in terms of the vector modal functions. The main focus of the present paper is the time-domain theory of a waveguide cavity, for which the excitation problem may be reduced to the solution of a number of modified Klein-Gordon equations. These modified Klein- Gordon equation are then solved by the method of retarded Green's function in order that the causality condition is satisfied. Numerical examples are also presented to demonstrate the time-domain theory. The analysis indicates that the time-domain theory is capable of providing an exact picture for the physical process inside a closed cavity and can overcome some serious problems that may arise in traditional time-harmonic theory due to the lack of causality.

Two kinds of band-notched ultra wide-band slot antennas are proposed. Printed on a dielectric substrate of FR4with relative permittivity of 4.4 and fed by a 50Ω microstrip line, the proposed antennas introduce semicircular annular strips to reject the frequency band (5.15-5.85 GHz) limited by IEEE802.11a. The parameters which affect the performance of the antennas in terms of its frequency domain characteristics are investigated in this paper.

Electrical tunability of a composite consisting of small ferroelectric spheres randomly dispersed into a dielectric background is studied. A new method to calculate the effective permittivity of such a nonlinear composite is introduced. The method is based on the Bruggeman effective medium theory and a specific model for the nonlinear permittivity of the ferrite. The resulting tunability (defined as a measure of the change in the permittivity due to the bias field) is a continuous function of the volume fraction of the ferroelectric material phase in the composite. As an example,SrTiO₃ is studied with two different nontunable background materials.

A hybridization approach to integrate simulation codes based on high and low frequency techniques is developed in this paper. This work allows the antenna design to be performed directly in the presence of the complex and large structures.Since the sizes of the complex structures can be extremely large electrically, and the antenna structure itself can be significantly complicated, such problems can not be resolved with a single technique alone.While low frequency techniques are generally applied for antenna design problems where small scale interactions are involved, high frequency techniques are adopted for the prediction of propagation effects inside the complex structures.The proposed hybridization approach provides a seamless integration of low and high frequency techniques that combines the advantages of both techniques in terms of accuracy and efficiency. Numerical example is presented to demonstrate the utilization of the proposed approach.

The fractional dual solutions of Maxwell equations in bi-isotropic medium are determined using the field decomposition approach. Both negative phase velocity and positive phase velocity propagation have been considered. The results are compared with the corresponding available results for isotropic and chiral medium. Time average power associated with fractional dual fields and corresponding source distribution are also studied.

The addition theorems are applied to analyze the normal incidence of plane waves onto infinitely long conducting or dielectric circular cylinders with multilayer coatings made of common and uncommon materials (ε_r, μ_r, σ) with the objective of minimization and maximization of radar cross-section (RCS). TE, TM and circular polarizations of the incident wave are considered. Optimization of RCS by the method of least squares leads to the determination of layer thicknesses and the material complex permittivities and permeabilities. A sensitivity analysis of RCS with respect to the geometrical and material parameters of the multilayer coated conducting cylinder is also performed. It is observed that broadband reduction of RCS is mostly achievable by a combination of conventional materials (ε_r, μ_r > 1), and unconventional materials (0 < ε_r, μ_r < 1) and lossy materials (σ > 0). It is seen that RCS reduction is due to the diversion and dissipation of radar signals. The results agree very well with the experimental and theoretical data available in the literature.

A hybrid method to calculate mutual coupling of electric or magnetic current elements on a cylindrically layered structure using closed-form Green's functions is presented. When ρ = ρ' and φ is not very close to φ , closed-form Green's functions are employed in the calculation of MoM matrix entries. When both ρ = ρ' and φ = φ' , series representation of the spectral domain Green's functions do not converge, therefore closed-form Green's functions can not be employed. In that case MoM matrix entries are evaluated using the proposed hybrid method. The technique is applied to both printed dipoles and slots placed on a layered cylindrical structures. The computational efficiency of the analysis of mutual coupling of printed elements on cylindrically layered geometries is increased with the use of proposed hybrid method which employs closed-form Green's functions.

In this paper, UWB Direction of Arrival (DoA) estimation using channelization receiver architecture proposed in [1] is extended to cover the case of multiple UWB emitters employing Time Hopping Spread Spectrum (TH-SS) multiple access technique. The DoA estimation is based on the spectral lines extracted from the channelizer. When considering the multiple-emitter case, these spectral lines are dependent on the hopping sequences assigned to the emitters (as derived in [2]). The principle behind the proposed method is to set the channelizer's frequencies at which only the spectral lines from the desired UWB emitter are present while those from the other emitters are absent. This requires a proper design of the hopping sequences that govern the transmission of all emitters. First, an additive white Gaussian noise channel is considered to demonstrate the fundamental principle. Then, the estimation in a realistic multipath channel is addressed. Simulation results show that the direction finding function successfully indicates the DoA of the desired signal when the channelizer's frequencies are set for the detection of that signal.

In this paper a dual band circularly polarized antenna is designed, fabricated, and measured. Based on the concept of composite right and left handed (CRLH) metamaterials, the same phase constants and current distributions on the ring antenna are achieved at two frequency bands. Thus, the antenna has similar radiation patterns at both bands. The circular polarization is implemented by feeding two vertical ports from power dividers that provide equal magnitudes and quadrature phase excitations.

A novel dual-band planar filter is proposed in this paper. It is shown that the two transmission bands can be excited and designed using proposed resonators which combine different sizes of open-loop resonators. The main resonators control the low-band resonant frequency and the sub resonators control the high-band resonant frequency. With 0^◦ feed structures added, the frequency selectivity of the filter is greatly improved. And the proposed filter also has advantages as low insertion loss and miniature size. The measurement of the filter is in good agreement with the simulation.