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.

Central Force Optimization (CFO) is a new deterministic multi-dimensional search metaheuristic based on the metaphor of gravitational kinematics. It models "probes" that "fly" through the decision space by analogy to masses moving under the influence of gravity. Equations are developed for the probes' positions and accelerations using the analogy of particle motion in a gravitational field. In the physical universe, objects traveling through threedimensional space become trapped in close orbits around highly gravitating masses, which is analogous to locating the maximum value of an objective function. In the CFO metaphor, "mass" is a userdefined function of the value of the objective function to be maximized. CFO is readily implemented in a compact computer program, and sample pseudocode is presented. As tests of CFO's effectiveness, an equalizer is designed for the well-known Fano load, and a 32-element linear array is synthesized. CFO results are compared to several other optimization methods.

In this paper,pattern search (PS) algorithms are introduced as a new tool for array thinning. It is shown that by selection of a fitness function which controls more than one parameter of the array pattern,and also by proper setting of weight factors in fitness function,one can achieve very good results. The method is tested on linear arrays of isotropic and non-isotropic elements and is shown to be useful in both cases. Mainlobe scanning to different angles is also tested and the results are success. In all cases studied in this paper,relativ e sidelobe level (SLL) is less than −20 dB with only small increase in mainlobe beamwidth compared to the case of a uniform array. Results of PS optimization are compared in two cases,whic h their starting points of optimization are different from each other. There is also a comparison made between results of array thinning using Genetic Algorithm (GA) and PS,and PS is shown to be a fast and reliable algorithm to be used in array thinning problem.

A microwave technique is proposed to measure the permittivity function of inhomogeneous dielectric walls. The measured reflection or transmission coefficients are used to extract the permittivity function of the dielectric walls. To solve the problem an optimization-based procedure is used. The usefulness of the proposed method is verified using some examples.

An analytical solution is presented for the electromagnetic scattering from a perfect electromagnetic conducting circular cylinder, embedded in the dielectric half-space. The solution utilizes the spectral (plane wave) representations of the fields and accounts for all the multiple interactions between the buried circular cylinder and the dielectric interface separating the two half spaces.

A novel dual-band bandpass filter with meander-loop resonator and complement split-ring resonator (CSRR) defected ground structure (DGS) is proposed in this letter. Microstrip meanderloop resonator and CSRR DGS are operated for respective passbands. Several finite attenuation poles in stopbands are realized to improve the selectivity of the proposed bandpass filter and isolation between the two passbands. Compact size,dual band and high selectivity characteristics are realized by this type of filter structure. The filter is evaluated by experiment and simulation with very good agreement.

A direct sub-domain moment-method formulation is presented for the analysis of arrays of thin-wire loops. Curved piecewise sinusoidal basis functions are used for the description of the currents on the loops, while both point matching and reaction matching are examined as testing schemes. Numerical results are provided for representative array structures with the intention to delve into the behavior of the solutions as the number of basis/testing functions grows, but also for the purpose of comparison with well-documented results. Finally, the complexity of the developed codes is estimated and general guidelines are provided for the efficient and accurate analysis of multi-element arrays.

A novel dual-mode dual-band bandpass filter based on conventional triangular dual-mode filter is designed in this paper. The filter has the characteristics of compact structure, low insertion loss and so on. Based on the current design schemes, the design of dualmode and dual-band filter can be integrated in a novel filter structure. Several attenuation poles in the stopband are realized to improve the selectivity of the proposed bandpass filter. The experimented results were in good agreement with simulated results.

A simplified method to obtain the complete set of the dyadic Green's functions (DGFs) for general anisotropic media is presented. The method is based on the k-domain representation of the fields in terms of wave matrices. The Fourier transformed Green's functions are calculated through the inverses of wave matrices. The inverses of the wave matrices, which lead to the final form of DGF, are obtained using dyadic decomposition technique. This facilitates the inverse operation significantly and gives DGFs clear vector representation, which helps their physical interpretation. The dyadic decomposition of the wave matrices has been presented for uniaxially anisotropic, biaxially anisotropic and gyrotropic media. The method of deriving DGF using the technique given in this paper is applied on a uniaxially anisotropic medium and verified with the existing results. It is shown that the knowledge of the inverse of one type of wave matrix is adequate to find the complete set of the dyadic Green's functions for a general anisotropic medium using the method presented. The duality relations of dyadic Green's functions are also developed. It is shown that once the dyadic Green's functions for one of the dual media are obtained, the DGFs for the other dual medium can be found by application of the duality relations shown in this paper.