A triple-band omni-directional antenna which comprises three pairs of dipoles placed back to back and printed on a dielectric substrate is presented. A prototype is constructed and tested. The experimental results show that the 10 dB return loss bandwidth (VSWR < 2.0) in 2.4 GHz, 5.2 GHz and 5.8 GHz reaches as much as 130 MHz, 500MHz and 200 MHz, respectively. Moreover, the radiation patterns are almost omni-directional in the azimuthal plane. Peak antenna gain is 1.63 dBi, 2.36 dBi and 1.54 dBi, which indicate that the proposed antenna can be used as a triple-band antenna for the WLAN application.

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.

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.

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.

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.

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.

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.

The characteristics of the guided electromagnetic wave propagation through a slab waveguide of uniaxially anisotropic dispersive metamaterial are investigated. Taking the cold plasma media model with ω_mpz < ω_mp⊥ < ω_ep⊥ as an example,the mode classification established in terms of the operating angular frequency ω₀ of the slab waveguide. The results indicate that the mode properties are closely dependent on the frequency. When ω² _mpz < ω²₀ < ω²_mp⊥ there are infinite guided modes. It is also found that when ω²_em < ω²₀ < ω²_mpz,there may be multiple solutions of the propagating mode with imaginary transverse wave number in a slab waveguide with thickness less than a certain value.

The propagation properties of surface plasmon polaritons (SPP) modes in nanoscale narrow metallic structures: gap, channel, and rectangular-hole waveguides, are analyzed by the complex effective dielectric constant approximation. The results show that all the SPP modes exist below the critical frequency where the real part of metal permittivity is negative unity. It is found that both cutoff frequency and cutoff height exist in channel waveguide and rectangularhole waveguide. The channel and rectangular-hole waveguides have different propagation properties at cutoffs due to their different cutoff conditions. Compared with the gap waveguide, the channel waveguide has shorter propagation length and better confinement when the operation frequency is near the critical frequency, but has longer propagation length and worse confinement when the operation frequency is far from the critical frequency. Among the three waveguides, the rectangular-hole waveguide has the best confinement factor and the shortest propagation length. The comprehensive analysis for the gap, channel, and rectangular-hole waveguides can provide some guidelines in the design of subwavelength optical devices.

The suitable use of an array antenna at the base station of a wireless communication system can result in improvement in signalto- interference ratio (SIR). In the present work, we consider circular array (CA) and concentric circular antenna array (CCAA) that are used for smart antenna systems. The performance criteria for SIR improvement is employed in this paper, is the spatial interference suppression coefficient. We first develop the expression of this figure of merit for CCAA and then analyze and compare the SIR performance for various configurations of eight and nine elements of CA and CCAA, with and without the element in the center by using circular patch antenna are provided. In addition, the effect of mutual coupling (MC) is taken into account.

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.

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.

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.

Multimode fibers are characterized by multipath propagation of optical signals and this leads to severe intersymbol interference at the output of the fiber. In this work an approach based on the Rake receiver is proposed to overcome this drawback. An optimization algorithm was developed and appropriate software was employed to apply the proposed methodology on specific multimode fiber. Extensive simulation results were produced and are presented herein. The numerical results have shown that the order of magnitude of the maximum data rate, R, supported at different CDMA gains, in order to achieve a Bit Error Rate value smaller or equal to a convergent point, is related to the length of the multimode fiber, L, by the expression R = dL⁻¹ with d increasing from 10⁶ to 10⁷ (Kbps. m) when CDMA gain increases from 50 to 500.

In this paper, a generalized photon wave function (PWF) which is applicable to electromagnetic problems is introduced. The formulation treats the electromagnetics fields as quantum mechanical entities. The introduced PWF is especially useful for boundaryvalue problems. For instance,the reflection coefficient at a dielectric half space is calculated based on the concepts of PWF and quantum mechanics. With the proposed method, inhomogeneous media, both isotropic and anisotropic, can also be analyzed. It is shown that by defining certain new variables, such as effective charges and effective currents, we will be able to describe the behavior of electromagnetic fields by the proposed photon wave function. At the end of this paper, a new FDTD method based on the notion of photon wave function is introduced and the resonance frequencies of a cubic cavity are obtained.

Vector wave three-dimensional (3-D) conducting rough surface scattering problem solved by a UV method with multilevel partitioning (UV-MLP) is developed in this paper. For a 3-D conducting rough surface scattering problem, the scattering structure is partitioned into multilevel block. By looking up the rank in the static problem, the impedance matrix for a given transmitting and receiving block is expressed into a product of U and V matrix. The UV method is illustrated by applying to a 3D scattering problem of random conducting rough surface in this paper. Numerical simulation results are illustrated.

A Ku band six-bit phase shifter is presented in this work. The developed phase shifter consists of four bits realized as periodically loaded-line and two bits based on novel switched-line with loaded-line. A 71Ω line impedance is chosen for the main transmission line in order to reduce the diode loss. Every bit has special tuning elements for the fine tuning of the required phase shift. The phase error for the 64 phase states is not greater than 3.4 degrees at the designed center frequency of 15 GHz, and the insertion loss for the 64 phase states is 5.2 dB±1.1 dB over the operating bandwidth of 14.9-15.1 GHz.

The aim of this work is to introduce the application of wavelet in Electromagnetic Scattering and making improvement in the moment method development. The conventional moment method basis and testing functions are used to digitalize the integral equations of the electric or magnetic field, resulting in dense matrix impedance. By using the wavelet expansion, wavelets as basis and testing functions, a sparse matrix is generated from the previous moment method dense matrix, which may save computational cost. Here application has been made upon two types of two dimensional antennas, which are circular cylindrical antennas and parabolic reflector antennas. Results are compared to the previous work done and published, excellent results are obtained.

This paper describes a steerable broadband dielectric antenna with 30% fractional bandwidth, operating at 11 GHz. The structure consists of a hollow cylindrical dielectric pellet of permittivity 6 fed by four probes. Two methods are described for beam forming: 1- Beam forming has been achieved by individually switching between excited probes. The switched excitation mechanism provides the antenna with a reconfigurable radiation beam that can be moved in the azimuth plane. 2- Variable phase excitation of several probes. Complete azimuth sweep was demonstrated by both methods, allowing any desired angle of beam directions. Simulation and experimental results are presented to illustrate the advantages of both designs.

A conformal cylindrical dipole array is developed in this paper. Because the conformal dipole array is curved, new far field pattern behaviors emerge. In this paper, we start to analyse the equations for the far field of the conformal dipole array by using the method of moments (MoM) with a dyadic Green's function, and then validate the accuracy of the far field expressions. Next, a novel Gauss amplitude distribution, which is capable to yield a desired far field radiation pattern when the array structure has a relative small cylindrical radius, is proposed. The advantage of the proposed method is that it can provide good aperture distributions to obtain low sidelobe level.