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2007-10-17 PIER Vol. 78, 437-455, 2008. doi:10.2528/PIER07092505

Quasi-Metallic-Wall Technique for Increasing the Efficiency of CB-CPW Antennas

Mourad Nedil, Mohamed Adnane Habib, Tayeb Denidni, and Halim Boutayeb

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.

2007-10-17 PIER Vol. 78, 421-436, 2008. doi:10.2528/PIER07100202

High Gain Rectangular Broad Band Microstrip Antenna with Embedded Negative Capacitor and Chip Resistor

Adnan Kaya

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.

2007-10-03 PIER Vol. 78, 393-419, 2008. doi:10.2528/PIER07091401

Novel Microstrip Hairpinline Narrowband Bandpass Filter Using via Ground Holes

Azhar Hasan and Ahmed Nadeem

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 εr 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.

2007-10-04 PIER Vol. 78, 377-392, 2008. doi:10.2528/PIER07091302

A Theoretical Study of Electromagnetic Transients in a Large Plate Due to Voltage Impact Excitation

Saurabh Kumar Mukerji, Ghanshyam Singh, Sandeep Goel, and Seema Manuja

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.

2007-09-29 PIER Vol. 78, 361-376, 2008. doi:10.2528/PIER07090403

Solution of an Integro-Differential Equation Arising in Oscillating Magnetic Fields Using HE's Homotopy Perturbation Method

Mehdi Dehghan and Fatemeh Shakeri

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.

2007-09-29 PIER Vol. 78, 349-360, 2008. doi:10.2528/PIER07092004

Pulse Preserving Capabilities of Printed Circular Disk Monopole Antennas with Different Substrates

Qi Wu, Rong-Hong Jin, and Jun-Ping Geng

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.

2007-09-29 PIER Vol. 78, 329-347, 2008. doi:10.2528/PIER07091002

Field Analysis of Dielectric Waveguide Devices Based on Coupled Transverse-Mode Integral Equation - Mathematical and Numerical Formulations

Hung-Wen Chang and Meng-Huei Sheng

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.

2007-09-29 PIER Vol. 78, 321-328, 2008. doi:10.2528/PIER07090801

Miniaturized Circularly-Polarized Antenna Using Tapered Meander-Line Structure

Jian-Feng Li, Bao-Hua Sun, Hai-Jin Zhou, and Qi-Zhong Liu

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.

2007-09-26 PIER Vol. 78, 301-320, 2008. doi:10.2528/PIER07091305

High Bit Rate Dense Dispersion Managed Optical Communication Systems with Distributed Amplification

Manoj Mishra and Swapan Konar

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.

2007-09-25 PIER Vol. 78, 285-300, 2008. doi:10.2528/PIER07091405

Radiation from Open-Ended Circular Waveguides: a Formulation Based on the Incomplete Hankel Functions

Renato Cicchetti and Antonio Faraone

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.

2007-09-25 PIER Vol. 78, 265-283, 2008. doi:10.2528/PIER07091004

A Fuzzy Model for Computing Input Impedance of Two Coupled Dipole Antennas in the Echelon Form

Saeed Reza Ostadzadeh, Mohammad Soleimani, and Majid Tayarani

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.

2007-09-25 PIER Vol. 78, 255-264, 2008. doi:10.2528/PIER07090102

An Innovative Portable Ultra Wide Band Stereophonic Radio Direction Finder

Shubhendu Joardar, Minakshi Jaint, Vasudev Bandewar, and Ashit Bhattacharya

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.

2007-09-21 PIER Vol. 78, 219-253, 2008. doi:10.2528/PIER07090605

Time-Domain Theory of Metal Cavity Resonator

Geyi Wen

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.

2007-09-20 PIER Vol. 78, 209-218, 2008. doi:10.2528/PIER07091201

Two Novel Band-Notched UWB Slot Antennas Fed by Microstrip Line

Guang-Min Zhang, Jing-Song Hong, and Bing-Zhong Wang

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.

2007-09-20 PIER Vol. 78, 189-207, 2008. doi:10.2528/PIER07081502

Tunability of Granular Ferroelectric Dielectric Composites

Liisi Jylha and Ari Sihvola

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.

2007-09-19 PIER Vol. 78, 173-187, 2008. doi:10.2528/PIER07091104

Hybridization of Simulation Codes Based on Numerical High and Low Frequency Techniques for the Efficient Antenna Design in the Presence of Electrically Large and Complex Structures

Hsi-Tseng Chou and Heng-Tung Hsu

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.

2007-09-19 PIER Vol. 78, 159-172, 2008. doi:10.2528/PIER07090701

Fractional Duality in Homogeneous BI-Isotropic Medium

Sajid Naqvi, Muhammad Faryad, Qaisar Naqvi, and Musarat Abbas

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.

2007-09-19 PIER Vol. 78, 129-157, 2008. doi:10.2528/PIER07090305

Ultra Wide Band RCS Optimization of Multilayerd Cylindrical Structures for Arbitrarily Polarized Incident Plane Waves

Homayoon Oraizi and Ali Abdolali

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 (εr, μr, 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 (εr, μr > 1), and unconventional materials (0 < εr, μr < 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.

2007-09-18 PIER Vol. 78, 103-127, 2008. doi:10.2528/PIER07082101

Mutual Coupling of Printed Elements on a Cylindrically Layered Structure Using Closed-Form Green's Functions

R. Acar and Gülbin Dural

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.

2007-09-18 PIER Vol. 78, 83-101, 2008. doi:10.2528/PIER07091303

Multiple UWB Emitters DOA Estimation Employing Time Hopping Spread Spectrum

Joni Lie, Boon Ng, and Chong Meng S. See

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.

2007-09-17 PIER Vol. 78, 73-81, 2008. doi:10.2528/PIER07082902

A Dual Band Circularly Polarized Ring Antenna Based on Composite Right and Left Handed Metamaterials

Ang Yu, Fan Yang, and Atef Elsherbeni

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.

2007-09-13 PIER Vol. 78, 61-71, 2008. doi:10.2528/PIER07081501

Thinned Arrays Using Pattern Search Algorithms

Aidin Razavi and Keyvan Forooraghi

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.

PIER Vol. 78, 49-59, 2008. doi:10.2528/PIER07082903

Modeling with NURBS Surfaces Used for the Calculation of RCS

Yan Zhao, Xiao-Wei Shi, and Le Xu

In this paper, the edge-facet model is transformed to the Non-Uniform Rational B-Spline (NURBS) model. The parameters of the knot vectors and the control points of NURBS are computed based on the data points on the surface of a target, and the NURBS model is constructed with the parameters. The degrees of the two parametric directions of a NURBS surface and the B-spline basis function are also analyzed. The relative errors between the NURBS models and the real models prove that the modeling method proposed in this paper is exact. Finally, the results of the Radar Cross Section (RCS) computed by the Physical Optics (PO) method with NURBS models are illustrated, and the results prove that the modeling method is of high precision and can be widely used in computational electromagnetics techniques.

2007-09-11 PIER Vol. 78, 39-48, 2008. doi:10.2528/PIER07082703

Identification of Inhomogeneous OR Multilayer Dielectric Walls

Mohammad Khalaj-Amirhosseini

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.

2007-09-11 PIER Vol. 78, 25-38, 2008. doi:10.2528/PIER07081601

Electromagnetic Scattering from a Perfect Electromagnetic Conductor Cylinder Buried in a Dielectric Half-Space

Shakeel Ahmed and Qaisar Naqvi

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.

2007-09-11 PIER Vol. 78, 17-24, 2008. doi:10.2528/PIER07090301

Design of Novel Dual-Band Bandpass Filter with Microstrip Meander-Loop Resonator and CSRR DGS

Gao-Lei Wu, Wei Mu, DDD Li, and Yong-Chang Jiao

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.

2007-09-09 PIER Vol. 78, 1-15, 2008. doi:10.2528/PIER07071704

Accuracy and Complexity Assessment of Sub-Domain Moment Methods for Arrays of Thin-Wire Loops

Panagiotis Papakanellos

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.