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2007-09-14 PIER Vol. 77, 493-499, 2007. doi:10.2528/PIER07090502

Design of Miniature Planar Dual-Band Filter with 0° Feed Structures

Wei Xue, Chang-Hong Liang, DDD Li, and Jun-Wa Fan

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.

2007-09-14 PIER Vol. 77, 425-491, 2007. doi:10.2528/PIER07082403

Central Force Optimization: a New Metaheuristic with Applications in Applied Electromagnetics

Richard Formato

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.

2007-09-09 PIER Vol. 77, 417-424, 2007. doi:10.2528/PIER07090501

Novel Design of Dual -Mode Dual-Band Bandpass Filter with Triangular Resonators

Li-Peng Zhao, DDD Li, Zhi-Xi Chen, and Chang-Hong Liang

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.

PIER Vol. 77, 409-416, 2007. doi:10.2528/PIER07082803

Novel Dual-Mode Dual-Band Bandpass Filter Using Double Square-Loop Structure

Zhi-Xi Chen, DDD Li, and Chang-Hong Liang

A dual-mode dual-band bandpass microstrip filter using double square-loop structure is proposed in this paper. Each of the square-loop forms a dual-mode resonator with controllable respective passband. Two tuning patches placed symmetrically at the side of the perturbation patch are used to change the higher passband frequency, while while keeping the lower invariable. Several attenuation poles in the stopband are realized to improve the selectivity of the proposed bandpass filter. The filter is evaluated by experiment and simulation with good agreement.

2007-09-09 PIER Vol. 77, 391-408, 2007. doi:10.2528/PIER07082401

Simplified Formulation of Dyadic Green's Functions and Their Duality Relations for General Anisotropic Media

Abdullah Eroglu and Jay Kyoon Lee

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.

2007-09-07 PIER Vol. 77, 379-390, 2007. doi:10.2528/PIER07082504

Analysis and Design of a Rectangular Dielectric Resonator Antenna Fed by Dielectric Image Line through Narrow Slots

Asem Al-Zoubi, Ahmed Kishk, and Allen Wilburn Glisson

Analysis and design of a narrow aperture coupled rectangular dielectric resonator antenna (DRA) fed by dielectric image line (DIL) are presented. The modal expansion method is used to describe the fields in the dielectric resonator side and the change in the modal voltage of the image line at the aperture is developed to analyze the single element DRA. The DIL is connected to the Xband rectangular waveguide through a waveguide transition and DIL tapering is used to match between the waveguide and the DIL.

2007-09-07 PIER Vol. 77, 367-378, 2007. doi:10.2528/PIER07081002

Reduction of Crosstalk in Wavelength Division Multiplexed Fiber Optic Communication Systems

Ragini Tripathi, Ramgopal Gangwar, and Nar Singh

In this paper two new methods to reduce the crosstalk in WDM systems are presented. These two methods along with the present methods are analyzed and their performances are compared. The proposed methods yield better results. Both signal power and optical signal power to noise power ratio (OSNR) improve significantly.

2007-09-03 PIER Vol. 77, 357-365, 2007. doi:10.2528/PIER07080201

Measuring the Permittivity of Dielectric Materials Using STDR Approach

Gholamreza Moradi and Abdolali Abdipour

This paper presents a new approach for measuring dielectric properties of materials. The proposed approach is based on applying the synthetic time domain reflectometry to a dielectric filled waveguide. The compromising measurement results show that this algorithm can be successfully applied for measuring other parameters of the materials. Also, the approach has been successfully applied to detect the discontinuities of as a multi-section microstrip line. This approach is very useful in measuring the electromagnetic parameters of the different liquids, gels, and solid materials.

2007-09-03 PIER Vol. 77, 343-356, 2007. doi:10.2528/PIER07081901

Novel Microstrip Triangular Resonator Bandpass Filter with Transmission Zeros and Wide Bands Using Fractal-Shaped Defection

Jian-Kang Xiao, Qing-Xin Chu, and Sheng Zhang

Fractal microwave passive circuits are simple and novel structures that attract much attention recently, however, the fractal technique is dominantly applied in antennas. In this paper, some new characteristics of microstrip equilateral triangular patch resonator with fractal defection are analyzed, and novel fractal bandpass filters using equilateral triangular resonator are presented to implement high performances of multi-transmission zeros, wide passband and stopband, and low passband insertion loss as well as miniaturization. Using fractal defection in patch, multi higher order modes are inspired for coupling a much wider passband, and parasitical harmonics are effectively suppressed. A new bandpass filter with a wide passband of about 0.92 GHz (εr = 9.8) or 2.7 GHz (εr = 2.2), maximum passband insertion loss of less than 0.5 dB, and multi-transmission zeros at both sides of passband, and a second bandpass filter with wide passband and stopbands of more than 2 GHz are implemented. Compared with some literatures, sizes of the new filters reduced and performances are greatly enhanced. The proposed filters have compact and simple structures, small sizes, high selectivity and so on, and all these features are the requirement of wireless communication circuits.

2007-09-01 PIER Vol. 77, 329-342, 2007. doi:10.2528/PIER07082501

A Numerical Study on Time- Reversal Electromagnetic Wave for Indoor Ultra-Wideband Signal Transmission

Shao-Qiu Xiao, Jian Chen, Bing-Zhong Wang, and Xiao-Fei Liu

In this paper, the propagation of ultra-wideband (UWB) pulse based on time reversal (TR) technique is studied by finitedifferent time-domain method in indoor environment. Time compression and spatial focusing of TR waveform are simulated and the propagation of multi-waveform string is analyzed. Then UWB wireless signal transmission based on TR concept is studied numerically. The studied results indicate that the UWB communication based on TR technique can obtain better Inter-Symbol Interference (ISI) and Co- Channel Interference (CCI) performance than traditional one because of its unique property.

2007-09-01 PIER Vol. 77, 309-328, 2007. doi:10.2528/PIER07081401

Time Domain Analysis of Active Transmission Line Using FDTD Technique (Application to Microwave/mm - Wave Transistors)

Kambiz Afrooz, Abdolali Abdipour, Ahad Tavakoli, and Masoud Movahhedi

In this paper, an accurate modeling procedure for GaAs MESFET as active coupled transmission line is presented. This model can consider the effect of wave propagation along the device electrodes. In this modeling technique the active multiconductor transmission line (AMTL) equations are obtained, which satisfy the TEM wave propagation along the GaAs MESFET electrodes. This modeling procedure is applied to a GaAs MESFETs by solving the AMTL equations using Finite-Difference Time-Domain (FDTD) technique. The scattering parameters are computed from time domain results over a frequency range of 20-220 GHz. This model investigates the effect of wave propagation along the transistor more accurate than the slice model, especially at high frequencies.

2007-08-30 PIER Vol. 77, 285-307, 2007. doi:10.2528/PIER07082102

Scattering of Obliquely Incident Plane Wave by an Array of Parallel Concentric Metamaterial Cylinders

Bassem Henin, Mohamed Al Sharkawy, and Atef Elsherbeni

A rigorous semi-analytical solution is presented for electromagnetic scattering from an array of parallel-coated circular cylinders of arbitrary radii and positions due to an obliquely incident TMz plane wave excitation. In order to check the validity of this technique, the radar cross-section of a single coated cylinder, a linear array of cylinders, and an arbitrary position array of cylinders are calculated and compared with available data in the literature. Furthermore, the near field is calculated to prove the validity of the boundary conditions on the surface of any cylinder with obliquely incidence wave. As an application, circular metamaterial cylinders are used to show the effect of metamaterial characteristics in altering the forward and backward scattering and in focusing the near field around the objects.

2007-08-30 PIER Vol. 77, 281-284, 2007. doi:10.2528/PIER07082502

Study on the Impedance-Matching Technique for High-Temperature Superconducting Microstrip Antennas

Shu-Fang Liu, Xiao-Wei Shi, and Shao-Dong Liu

Impedance-Matching technique is in common use for antennas to broaden their bandwidth. Its application in hightemperature superconducting microstrip antennas is studied theoretically in this paper. It is found that employing an impedance-matching network directly to HTS microstrip antennas to broaden their bandwidth is of little significance.

2007-08-30 PIER Vol. 77, 273-280, 2007. doi:10.2528/PIER07082302

A Novel and Compact UWB Bandpass Filter Using Microstrip Fork-Form Resonators

Hui Chen and Yu-Xing Zhang

A novel and compact ultra wideband (UWB) bandpass filter (BPF) with two transmission zeros near both passband edges of lower and higher frequency is proposed by using a new structure of fork-formresonators. The fork-formresonator generates a attenuation pole at the higher passband edge, lower insertion loss, wider bandwidth and compacter dimension, as compared with the traditional parallel unilateral-coupled resonator. A microstrip bandpass filter cascaded by two stages fork-formresonators with a 3-dB fractional bandwidth of 128% (from1.0 GHz to 4.6 GHz) is designed, fabricated, and tested. The measured characteristics of the filter agree with the theoretical simulations, and the measured results show good specifications which are very low insertion loss 0.5±0.3 dB within the passband and good return loss less than −15 dB from1.5 GHz to 4.0 GHz, respectively.

2007-08-30 PIER Vol. 77, 267-272, 2007. doi:10.2528/PIER07081702

An Expression for the Radar Cross Section Computation of an Electrically Large Perfect Conducting Cylinder Located Over a Dielectric Half-Space

Xiao-Jie Chen and Xiao-Wei Shi

A method is presented to calculate the monostatic Radar Cross Section (RCS) of an electrically large perfect conducting cylinder vertically located over a dielectric half-space using Physical Optics (PO) technique. The four-path modal method is used to approximate the influence of the half-space to the scattering mechanism. The comparison between the results calculated by this expression and that by Moment Method (MOM) show that the expression is effective and efficient.

2007-08-27 PIER Vol. 77, 243-266, 2007. doi:10.2528/PIER07072903

Linear and Nonlinear Superimposed Bragg Grating: a Novel Proposal for All-Optical Multi-Wavelength Filtering and Switching

Hassan Ghafoori-Fard, Mohammad Moghimi, and Ali Rostami

In this paper, the linear and nonlinear applications including optical filtering and switching of superimposed Bragg grating are presented. For realization of superimposed Bragg grating electrooptic effect is used. The introduced system acts as an optical chip. The induced superimposed index of refractions due to sampled electric potentials applied through metallic strips on electro-optically active core-cladding are investigated analytically and simulated numerically using the Transfer Matrix Method (TMM). It is shown that the applied electric field induces superimposed refractive index grating, which can be controlled using amplitudes and frequency contents of potential samples as well as optical waveguide parameters. Our proposed structure is analog programmable device for realization of many interesting optical signal conditioners such as optical filters, optical beam splitters, and many other special transfer functions in linear case. The proposed device is tunable and can be controlled using the applied potential parameters (samples) and easily satisfy dense wavelength division multiplexing (DWDM) system demand specifications. The electro-optic Pockels effect for generation of the superimposed gratings in this building block will be used. Then we propose an optical chip for performing the introduced functions. In practical cases, for realization of DWDM demands, we need very large number of potential samples approximately 3 to 4 orders of magnitudes. So, this type of block as optical controllable chip really from practical point of views is impossible and illegal. In this paper, we will present a simple approach for decreasing the number of efficient control samples from outside for managing the proposed tasks. Our calculations in this paper shows that with less than approximately 200 control pins, we can realize all of proposed practical ideas with acceptable precision. Also, with 3 samples per period, our design will cover 215 individual DWDM channels theoretically from 1.55um towards lower wavelengths and 325 channels for 4 samples per period case, which is infinity from practical point of views. All of transfer functions corresponding to these channels can be manipulated using applied potential samples. Also, as nonlinear applications of the superimposed Bragg grating multi-wavelength optical switching is presented. For this purpose the switching operation is illustrated first and then switching thresholds in the case of three predefined wavelengths are shown. Thus we illustrate numerical results for demonstration of the ability of the proposed structure. At the same time, we investigate effects of the parameters of the proposed structure such as the nonlinear refractive index and the grating length (number of layers) on switching performance including threshold intensity and slope of transition function. The proposed structure can be used as multi-wavelength switching applicable to DWDM and multi wavelength communication systems.

2007-08-24 PIER Vol. 77, 225-242, 2007. doi:10.2528/PIER07081804

Interaction of Dual Band Helical and PIFA Handset Antennas with Human Head and Hand

Mohammad Ali Ebrahimi-Ganjeh and Amir Attari

Helical antenna and planar inverted-F antenna (PIFA) are two commonly used handset antennas. This paper presents a comprehensive study on the performance of a dual band PIFA and a dual band helical antenna designed for operating in GSM900 and DCS1800 frequency bands. Radiation patterns and VSWR of these antennas are computed in free space as well as in the presence of head and hand. The specific absorption rate (SAR) of the helical antenna is calculated and compared with that of the PIFA handset antenna. The peak average SAR in the head is compared with SAR limits in the safety standards and so the maximum radiation power of each antenna is determined. In addition, radiation efficiencies of these handset antennas are computed in the presence of head and hand. All numerical simulations are performed using the Ansoft HFSS software. Numerical simulations results are in good agreement with published measurement results.

2007-08-24 PIER Vol. 77, 215-224, 2007. doi:10.2528/PIER07081602

Backscattering of Electrically Large Perfect Conducting Targets Modeled by NURBS Surfaces in Half-Space

Xiao-Jie Chen and Xiao-Wei Shi

Backscattering Radar Cross Section (RCS) of electrically large targets is analyzed using Physical Optics (PO) approximation. The targets are located in a dielectric half-space,and modeled with Nonuniform Rational B-spline (NURBS) surfaces. The influence of the half-space is considered by the "four-path" model approximation. Results show the validity of the method.

2007-08-24 PIER Vol. 77, 193-214, 2007. doi:10.2528/PIER07073103

Double Statistical Distribution of Conductivity and Aspect Ratio of Inclusions in Dielectric Mixtures at Microwave Frequencies

Marina Koledintseva, Richard DuBroff, Robert Schwartz, and James Drewniak

An analytical model of a composite dielectric presented in this paper is the extension of Maxwell Garnett formulation. It takes into account the simultaneous statistical (Gaussian) distribution of conductivity and aspect ratio of inclusions. The inclusions are randomly oriented elongated conducting spheroids at concentrations below the percolation threshold. The formulation presented herein is limited to microwave frequencies. However, taking subtle frequencydependent effects that play important part at optical frequencies into account is straightforward. Some results of computations of microwave complex effective permittivity of composites with different input parameters have been obtained using analytical and numerical integration in Maple 10 software. It is shown how the parameters of the distribution laws - mean values and standard deviations of aspect ratio and conductivity - affect the resultant complex effective permittivity. The results of computations demonstrate that the most important factors affecting frequency characteristics of microwave effective permittivity are the mean values of the aspect ratio and conductivity. As for the standard deviations of aspect ratio and conductivity, their effects are the most noticeable in the transition between the static and optical limits of the Debye characteristic for the effective permittivity. There is almost no effect in the static and "optic" regions of the Debye curves.

2007-08-24 PIER Vol. 77, 181-192, 2007. doi:10.2528/PIER07072504

An Efficient Hybrid Swarm Intelligence-Gradient Optimization Method for Complex Time Green's Functions of Multilayer Media

Mohsen Ghaffari-Miab, Amin Farmahini-Farahani, Reza Faraji-Dana, and Caro Lucas

A new hybrid technique for optimization of a multivariable function is proposed. This method is applied to the problem of complex time Green's function of multilayer media. This technique combines Particle Swarm search algorithm with the gradient based quasi-Newton method. Superiority of the method is demonstrated by comparing its results with other optimization techniques.

2007-08-23 PIER Vol. 77, 171-180, 2007. doi:10.2528/PIER07080604

A Perturbative Approach for the Evaluation of EM Scattering Properties from Arbitrary Dielectric Bodies with Inclusions

Leonardo Lucci

An approximate perturbative technique for the analysis of electromagnetic scattering from dielectric bodies of arbitrary shape containing dielectric inclusions, illuminated by an arbitrarily polarized incident plane wave, is investigated. The perturbative approach here presented allows for the efficient computation of the scattering properties of a given body as the inclusions vary, with a formulation solving only for the inclusion bound field component.

2007-08-23 PIER Vol. 77, 149-170, 2007. doi:10.2528/PIER07081201

A Novel Proposal for Ultra-High Resolution and Compact Optical Displacement Sensor Based on Electromagnetically Induced Transparency in Ring Resonator

Reza Yadipour, Karim Abbasian, Ali Rostami, and Zia Koozekanani

In this paper a novel method for ultra-high-resolution, compact and tunable optical displacement sensor using ring resonator and electromagnetically induced transparency (EIT) is proposed. The introduced technique uses ring resonator as an interesting element including high quality factor. We show that the proposed sensor can easily detect well below nanometer ranges. It is shown that the proposed idea of using EIT the resolution of the sensor is so high for displacement below mm range and for ranges larger than mm the sensitivity of the proposed sensor in both EIT and traditional cases is same approximately. Also, the proposed sensor is optically tunable. So, depends on required resolution optical control field can be used to tune the sensitivity of the proposed device.

2007-08-20 PIER Vol. 77, 137-148, 2007. doi:10.2528/PIER07080701

A Modified Microstrip-Fed Two-Step Tapered Monopole Antenna for UWB and WLAN Applications

Reza Zaker, Changiz Ghobadi, and Javad Nourinia

This paper presents a novel modified Printed Tapered Monopole Antenna (PTMA)for ultra wideband (UWB)wireless communication applications. The proposed antenna consists of a truncated ground plane and two-tapered radiating patch separated by a slot (air gap)of different slopes, which provides a wideband behavior and relatively good matching. Moreover, the effects of a modified T-shaped slot inserted in the first tapered patch, on the impedance matching is investigated. The antenna has a small area of 23 × 26.5mm2 and offers an impedance bandwidth as high as 100% at a centre frequency of 7.2 GHz for S11 < −10 dB, which has an area reduction of 15% and a frequency bandwidth increment of 72% with respect to the previous similar antenna. The presented antenna covers the 5.2/5.8 GHz WLAN and 5.5 GHz WIMAX operating bands. Numerical analysis using Ansoft HFSS and measurement results is also presented in the paper.

2007-08-20 PIER Vol. 77, 121-136, 2007. doi:10.2528/PIER07071803

An Efficient Modeling with GA Approach to Retrieve Soil Texture, Moisture and Roughness from ERS-2 SAR Data

Dharmendra Singh and Asutosh Kathpalia

One of the most important functions of radar remote sensing is to retrieve the soil moisture and surface parameters where surface parameters generally includes soil surface roughness and texture of soil (i.e.,% of coarse sand,silt and clay). Variation of soil moisture and surface parameters changes the soil permittivity, and affects the observation of the radar wave scattering (σ0). How to invert the moisture and surface parameters from radar data has been one of the most interesting problems to be resolved. Still,v ery few reported work is available to retrieve the soil textures with radar data. Therefore,in present paper an attempt has been made to retrieve the soil textures with soil moisture and surface roughness from Synthetic Aperture Radar (SAR) data. In this case number of variables are more and it is difficult to invert and retrieve the various parameters. To overcome this difficulty,an approach based on Genetic Algorithm (GA) with inclusion of empirical modeling has been proposed to retrieve the soil moisture,roughness and soil texture with ERS-2 (European Remote Sensing) SAR (Synthetic Aperture Radar) data of Haridwar region of India. The retrieved surface parameters and moisture content with proposed approach show quite good agreement with observed values of soil moisture and surface parameters. This study infers that modeling with GA has great potential to retrieve several variables simultaneously with good results.

2007-08-15 PIER Vol. 77, 111-120, 2007. doi:10.2528/PIER07080302

Analysis of Transient Electromagnetic Scattering with Plane Wave Incidence Using MOD-FDM

Baek-Ho Jung and Tapan Kumar Sarkar

Recently, a marching-on in degree finite difference method (MOD-FDM) was employed in the finite-difference time-domain (FDTD) formulation to obtain unconditionally stable transient responses. The objective of this work is to implement a plane wave excitation in the MOD-FDM formulation for scattering problems for an open region. This formulation has volume electric and magnetic current densities related to the incident field in Maxwell's equations explicitly. Numerical results computed by the proposed formulation are presented and compared with the solutions of the conventional FDTD method.

PIER Vol. 77, 97-110, 2007. doi:10.2528/PIER07080102

Uniform Gain Power-Spectrum Antenna-Pattern Theorem and Its Possible Applications

Shubhendu Joardar and Ashit Bhattacharya

For certain applications in radio astronomy, viz. radio spectrographs, spectrum monitoring etc., only the amplitude power spectrum coverage within an angle of observation could be of interest. Ideally, the antenna structures of such instruments should illuminate this covering angle with a fixed uniform gain. This might be achieved using a combination of dipole antennas, a single vertical dipole, a loop antenna etc., but are subjected to limited bandwidth. This limitation could be overcome if many electrically-identical wideband antennas are positioned across the perimeter of a circle lying in the horizontal plane such that the antennas' adjacent half power beam angles touch each other. It has been theoretically observed that if two identical antennas are positioned at an angle with respect to one-another in such a way that their adjacent half power beam angles coincide, then if the amplitude power spectrums of the two are added, the result is effectively an amplitude power spectrum obtained from a single antenna having an uniform gain and uniform signal to noise ratio within the angle subtended by them. This angle also happens to be equal to the half power beamwidth of the individual antennas. A proper design using frequency independent antennas might possibly result to an user specified uniform amplitude power spectrum gain coverage across any required angle, with a theoretically unlimited bandwidth. More number of identical antennas might be positioned in similar fashion for extending the angular coverage. The power spectrums from these antennas could be directly added which effectively represent the power spectrum from a single antenna possessing uniform gain coverage within an angle equal to the product of individual half power beamwidth angle with one less the number of antennas, thus achieving user defined gain, wide bandwidth, and uniform signal to noise ratio across the angle. It is also possible to recover the time domain signal by applying Fourier Transform on the outputs of the antennas followed by an addition of their amplitudes while keeping the phase information identical to that of one antenna (taken as reference), and taking its inverse Fourier Transform.

2007-08-12 PIER Vol. 77, 85-96, 2007. doi:10.2528/PIER07072904

Complete Dispersion Analysis of Vivaldi Antenna for Ultra Wideband Applications

Aidin Mehdipour, K. Mohammadpour-Aghdam, and Reza Faraji-Dana

Besides the return loss and radiation pattern, dispersion characteristic of the antenna is one of the most important factors which should be considered in ultra wideband applications. In this paper, dispersion behavior of two specific Vivaldi antennas has been fully investigated in both frequency and time domains. All simulations are carried out by CST MS software. Moreover, by fabricating the antennas, the simulation results are verified by experimental data.

2007-08-08 PIER Vol. 77, 75-84, 2007. doi:10.2528/PIER07080202

Reconstruction of Inhomogeneous Dielectrics at Microwave Frequencies

Mohammad Khalaj-Amirhosseini

The transmission line techniques are generalized to measure the permittivity function of one-dimensional inhomogeneous dielectrics. A rectangular waveguide is used and the dielectric slab under test is placed at the input flange of it. Then the measured scattering parameters or the short-circuited reflection coefficient are used to extract the permittivity function of dielectric. To solve the problem an optimization-based procedure is used. The usefulness of the proposed method is verified using a comprehensive example.

2007-08-08 PIER Vol. 77, 67-73, 2007. doi:10.2528/PIER07072707

A Compact Square Loop Dual-Mode Bandpass Filter with Wide Stop-Band

Yun Xiu Wang, Bing-Zhong Wang, and Jian Wang

A new dual-mode microstrip bandpass filter with wide stop-band is presented using the square loop resonator with treeshaped patches attached to the four inner corners of the loop. The mode splitting is realized by introducing a small cut locating at a 45 offset from its two orthogonal modes. It is shown that the dual-mode filter has a wide stop-band including the first spurious resonance frequency. The center frequency can be tuned. Moreover, the proposed filter has a smaller size compared with conventional dualmode bandpass filters at the same central frequency.

2007-08-08 PIER Vol. 77, 55-65, 2007. doi:10.2528/PIER07072506

Study of the Band-Notch Function for Swallow-Tailed Planar Monopole Antennas

Hai-Jin Zhou, Qi-Zhong Liu, Ying-Zeng Yin, and Wen-Bo Wei

In this paper, we propose two swallow-tailed ultrawideband planar monopole antennas that exhibit notch characteristics in the IEEE802.11a frequency band (5.15-5.825 GHz) by inserting various slots into the antennas. The effects of the lengths of the slots on the notched frequency band are analyzed. The radiation patterns of the proposed antennas are also measured and the gains are shown to be flat, except in the notched frequency band.

2007-08-08 PIER Vol. 77, 43-54, 2007. doi:10.2528/PIER07072302

Compact Artificial Magnetic Conductor Designs Using Planar Square Spiral Geometries

Yanghyo Kim, Fan Yang, and Atef Elsherbeni

Compact spiral artificial magnetic conductors (AMC) have been investigatedin this paper. First, single andd ouble spirals are examinedto achieve an in-phase reflection at a lower frequency comparedto a conventional patch element of the same size. However, these two designs generate a large cross polarization. The cross polarization affects the operating frequency and bandwidth. In order to eliminate the cross polarization effect, a four-arm spiral element is introduced. This geometry does not generate a cross polarization, and an operating frequency that is 49.45% lower than the reference patch element has been achieved.

2007-08-01 PIER Vol. 77, 29-41, 2007. doi:10.2528/PIER07072301

Novel Microstrip Bandpass Filters with Transmission Zeros

Yong-Zhong Zhu and Yong-Jun Xie

Some design methods for band-pass filters based on halfwavelength resonators have been proposed. The main feature of these methods is that n or n + 1 transmission zeros can be generated for a structure composed of n resonators. To demonstrate the usefulness of the proposed filter structures, three kinds of two-pole compact microstrip hairpin filters are designed and fabricated. Good agreement between measured and simulated data has been demonstrated.

2007-08-01 PIER Vol. 77, 15-27, 2007. doi:10.2528/PIER07072202

Model the Electromagnetic Scattering from Three-Dimensional PEC Object Buried Under Rough Ground by MoM and Modified PO Hybrid Method

Hai Chen and Guo-Qiang Zhu

In this paper, method of moment and modified physical optical hybrid method is used to analyze the scattering from 3-D PEC object buried under rough surface. The random rough ground surface is characterized with Gaussian statistics for surface height and for surface correlation function. The air-earth interface and the object are all replaced by the corresponding equivalent currents and the equivalent current on the ground surface is divided into two parts: the current caused by the incident wave which is named as incident current, and the current caused by buried object which is named as scattered current. The incident currents are obtained by PO approximation and the scattered currents are related to the current on the buried scatter by a modified PO method in this work. Only the current of scatter is considered as unknown and will be solved by MoM. After obtaining the current of scatter, the scattered current on the ground surface is calculated by the modified PO approximation. And the scatter field will be calculated by using the scattered current. In order to validate the hybrid method proposed in this paper, several numerical examples are given and compared with the results of MoM.

2007-08-01 PIER Vol. 77, 1-14, 2007. doi:10.2528/PIER07072001

Ambiguity Functions of Direct Chaotic Radar Employing Microwave Chaotic Colpitts Oscillator

Zhi-Guo Shi, Shan Qiao, Kang Chen, Wan-Zhao Cui, Wei Ma, Tao Jiang, and Li-Xin Ran

The ambiguity functions of a kind of direct chaotic radar system are investigated. In this radar system, a microwave chaotic Colpitts oscillator is employed to generate the source signal that is directly transmitted through a wideband antenna without modulation. The auto-ambiguity function of this radar system shows many sidelobes which makes the unambiguous detection difficult. It is because the spectrum of the chaotic signal is not very flat and smooth, with pulsation peaks in it. The cross-ambiguity functions of the direct radar system have also been investigated to evaluate the electronic counter countermeasure (ECCM) performance and the "multi-user" characteristic. It is shown that rather excellent ECCM capability can be achieved in this radar system with transmitting chaotic signals generated by circuits with same parameters but at different time or with slightly different circuit parameters. In addition, several possible methods to reshape the spectrum of the chaotic signal from microwave Colpitts oscillators to improve the unambiguous detection performance are suggested at the end of this paper.