A novel microstrip quad-band bandpass filter was designed and fabricated on an Al₂O₃ ceramic substrate of 1 mm thick. Two different types of open-loop resonator --- a winding line-shaped resonator (WLR) and a stepped impedance resonator (SIR) --- were positioned in parallel at the two sides of input/output microstrip lines that had the same coupling lengths and coupling gap widths. The proposed filter was based on a WLR with four different resonant frequencies: 1.23 GHz, 2.49 GHz, 3.73 GHz, and 5.41 GHz. By carefully selecting the resonant frequencies of the two resonators to be slightly different, the phase difference for the signals in the two resonators was negative, indicating that energy cancellation occurred, resulting in wide bandwidths and deep transmission zeros. The spurious resonant frequencies of the SIR were designed to be non-integer multiples of the fundamental resonant frequency by adjusting the length, characteristic impedance ratio, and electrical length. The SIR was designed to have three resonant frequencies at around 2.27 GHz, 3.37 GHz, and 4.94 GHz, which had phase differences with the WLR's resonant frequencies of 2.49 GHz, 3.73 GHz, and 5.41 GHz. Finally, a novel quad-band filter with a narrow band in the L2-band (GPS, 1.227 GHz) and three wide bands in the WIMAX (3.5 GHz) and WLAN (2.4 GHz and 5.2 GHz) was achieved.

Organic-inorganic thermoplastic composites offer a cost-effective material choice with tuneable dielectric properties for various telecom components and applications. Typically such composites require substantial loading of inorganics to obtain a feasible level of permittivity at RF frequencies dramatically decreasing mechanical ruggedness and increasing losses. In this paper we demonstrate utilization of nanoparticle phase in BaSrTiO₃-polypropylene-graft-poly (styrene-stat-divenylbenzene) composite to enhance the high frequency properties and overcome the problems associated with high filler loading. The effect of nanosize silicon, silver and Al₂O₃ additives with different volume fractions in complex permittivity was investigated up to 1 GHz. Significant increase in the effective permittivity of the composites with all the additives was observe, especially in the case of the nanosized silver particles where only 2 vol.% addition was able to enhance ε_r by 52% without increasing the dielectric losses when compared to the reference sample.

In this paper, an improved CBFM/p-FFT algorithm is presented, which can be applied to solve electromagnetic scattering problems of large-scale periodic composite metallic/dielectric arrays, even when the array has electrically small periodicity or separating distance. Using characteristic basis function method (CBFM), scattering characteristics of any inhomogeneous targets can be represented by special responses derived from a set of incident plane waves (PWs). In order to reserve the dominant scattering characteristics of the targets and remove the redundancy of the overfull responses, a singular value decomposition (SVD) procedure is applied, then, new series of basis functions are built based on the left singular vectors after SVD whose corresponding singular values beyond a predefined threshold. However, the algorithm of CBFM combined with method of moments (MoM) still requires a lot of memory and CPU resources to some large scale problems, so the precorrected-fast Fourier transform (p-FFT) method is applied based on the novel built basis functions, with which, the required memory and solve time for solution can be reduced in an extraordinary extent. For a near correction technique is applied to process the interactions between cells placed within a distance less than a predefined near-far field threshold, arrays with electrically small periodicity can be analyzed accurately. Moreover, the incomplete LU factorization with thresholding (ILUT) preconditioner is applied to improve the condition number of the combined algorithm, which improves the convergence speed greatly.

An effective Nonlinear Schrödinger Equation for propagation is derived for optical dark and power law spatial solitons at the subwavelength with a surface plasmonic interaction. Starting with Maxwell's Nonlinear Equations a model is proposed for TM polarized type spatial solitons on a metal dielectric interface. Two separate systems are considered in which one metal dielectric interface has a dielectric Kerr medium that has self-defocusing and another similar interface which the dielectric Kerr medium that has self-focusing depending on the modulus of the electric field to some power law variable p. The beam dynamics are analytically studied for these nanowaveguides.

An improved composite right/left-handed (CRLH) unit cell optimized for a leaky-wave (LW) antenna is presented. This CRLH cell consists of a series of one transmission line, an interdigital capacitor, another transmission line and a shunt shorted stub. Introducing the transmission lines, the parasitic self-resonances of the capacitor are shifted outside the operational band, the radiation range is extended and the transition frequency at which the balanced cell condition is achieved can be chosen in the design process from a broader range of frequencies. The characteristics and performances of the proposed cell are verified by simulation and by measuring two artificial transmission lines.

The frequency shift of the transfer function of single layer composite materials has been analyzed and tested. The effects are studied by means of planar pseudo-elliptical filters in Ka waveguide. The filters, consisting of a frequency selective surface placed perpendicularly to the waveguide axis, have been realized by a high resolution photolithographic technique. Deviations of the experimental transfer functions from the simulation are analyzed with particular emphasis to the effect of metal thickness. The finite thickness of the metal constituting the frequency selective surface causes a shift of the transfer function towards high frequencies (blueshift), attributed to dipole-dipole interaction in the metal layer. Such an effect is only partially predicted by full wave analysis based on finite element method. The increase of the thickness determines a reduction of the attenuation for thickness values between 10 and 100 skin depths.

In this paper, a novel compact microstrip-fed ultra-wideband (UWB) step-slot antenna with a rotated patch is demonstrated and experimentally studied. With an effective combination of the step-slot and rotated patch and proper dimensions, bandwidth enhancement for UWB operation is obtained. From the simulated and measured results, the enhanced impedance bandwidth is brought up to about 117.5% from 2.88 to 11.08 GHz defined by 10 dB return loss. Details of the proposed antenna are described, and experimental results are presented and discussed.

We experimentally characterize the pulse propagation in two-dimensional composite right- and left-handed transmission lines periodically loaded with Schottky varactors. A properly designed line structure should produce that nonlinearity rendered by the varactors creating a self-focused pulse on the line and finally collapses, which allows it to be engineered for pulse processing systems. We built a test breadboard line and observed self-focused pulses.

In this paper, a novel narrowband frequency selective surface (FSS) with a stable performance based on substrate integrated waveguide technology is presented. The unit cell of the FSS consists of a double-sided metalized substrate with a circular hole and a SIW circular cavity. In this way, incident EM waves enter the circular cavity and excite a TM110 cavity resonance, leading to a narrow pass-band. The high-Q property of the TM110 cavity resonance provides a very good wide-angle and polarization-independent stability. Both the simulation and experimental results show that such narrowband FSS owes its advantages to high selectivity, low profile stable performance with various incident angles and different polarizations, which is suitable for impulse detections, narrow-band communications, electronic countermeasures, etc.

This paper presents a new method of sequential microwave filter tuning. For filters with R tuning elements (including cavities, couplings and cross-couplings), based on physically measured scattering characteristics in the frequency domain, the Artificial Neural Network (ANN) is used to build inverse models of R sub-filters. Each sub-filter is associated to one tuning element. The sub-filters are obtained by successive opening or shorting of resonators and by removing coupling screws. For each sub-filter, the ANN training vectors are defined as physical reflection characteristics (input vectors) and the corresponding positions of the tuning element, which is detuned, in both directions, from its proper setting (output vectors). In the tuning process, such inverse models are used for calculating the tuning element increments needed for setting the tuning element in the proper position. The tuning experiment, conducted on 8- and 11- cavity filters, has shown the performance of the presented method.

Synchronization performance of a pulse-based ultra-wideband (UWB) system is investigated by taking into account of distortions caused by transmitter and receiver antennas and wireless propagation channels in different environments. The synchronization scheme under consideration can be achieved in two steps: a slide correlator and a phase-locked loop (PLL)-like fine tuning loop. Effects of the non-idealities are evaluated by analyzing the distortion of the received UWB pulse and subsequently the synchronization performance of the pulse-based UWB system. It is found that generally a smaller step is required for the sliding correlator due to distortions introduced by the antennas and channels. However, the fine tuning loop can always be stabilized by adjusting the loop parameters. Therefore, synchronization can always be achieved.

The Multilook Cross Correlation (MLCC) is one of the most reliable algorithms used for Doppler ambiguity number estimation of the Doppler centroid parameter. However, the existing MLCC algorithm is only suitable for low contrast scenes. In high contrast scenes, the estimated result is not reliable, and the error is unacceptable. Besides, the Doppler centroid estimation processing time is long and can only be used in offline processing. In this paper, we introduce a modified MLCC algorithm that has better sensitivity which is suitable not only for low contrast scenes, but also for high contrast scenes. In addition, the modified MLCC algorithm can be implemented on parallel signal processing units for better time efficiency. Experiments with RADARSAT-1 data show that the modified algorithm works well in both high and low contrast scenes.

A rigorous modal theory of conical diffraction from curved strip gratings is presented. In this approach, the C-method with adaptive spatial resolution is used in conjunction with the combined boundary conditions. The method is successfully validated by comparison with a case where the solution can also be obtained in the Cartesian coordinate system.

In this paper two four-pole filters at X-band are presented, both designs use a coaxial quarter wavelength resonator suspended in air by short circuits between the coaxial center and outer conductor. Different couplings between suspended resonators have been used to obtain a Chebyshev and a quasi-elliptic response. The Chebyshev filter was designed to have a 9.2 GHz centre frequency with a 4% fractional bandwidth. The second design is a quasi-elliptic filter composed of two vertically stacked rectangular coaxial lines, where one pair of resonators is placed on the lower coaxial line and another pair is located on the upper line. Coupling between coaxial lines is achieved through an iris in the common coaxial ground plane. The quasi-elliptic filter has been designed to have a centre frequency of 9.1 GHz with a 4% fractional bandwidth. Two transmission zeros located at the sides of the passband have been successfully achieved with the proposed filter topology. Experimental results for both designs are presented, where a good agreement with simulations has been obtained.

Circular antenna array design is one of the most important electromagnetic optimization problems of current interest. The problem of designing a large multiple concentric planar thinned circular ring arrays of uniformly excited isotropic antennas is considered in this paper. This antenna must generate a pencil beam pattern in the vertical plane along with minimized side lobe level (SLL). In this paper, we present an optimization method based on an improved variant of one of the most powerful real parameter optimizers of current interest, called Differential Evolution (DE). Two sets of different cases have been studied here. First set deals with thinned array design with the goal to achieve number of switched off elements equal to 220 or more. The other set contains design of array while maintaining side lobe level (SLL) below a fixed value. Both set contains two types of design, one with uniform inter-element spacing fixed at 0.5λ and the other with optimum uniform inter-element spacing. The half-power beam width of the synthesized pattern is attempted to maintain fixed at the value equal to that of a fully populated array with uniform spacing of 0.5λ. Simulation results of the designed thinned arrays are compared with a fully populated array for all the cases to illustrate the effectiveness of our proposed method.

Excitation and propagation of a pulse electromagnetic wave in an open circular dielectric waveguide is considered. Partition of the pulse field into radiated wave, surface wave, and guided wave has been revealed and the corresponding physical effects are interpreted directly in the time domain. Namely it was shown that there is a precursor at the rod axis that propagates with speed of light in free space, it originates from the pulse surface wave that propagates along the rod surface and radiates into the rod in a Cherenkov like manner.

A novel self-similar antenna for band-notched ultra-wideband (UWB) applications is proposed. The UWB performance is obtained by introducing a quasi-trapezoidal radiating patch and a self-similar ground plane. By etching two similar slots on the radiating patch, band-notched characteristic can be obtained. The measured results show that the antenna covers the band of UWB from 2.6 to 12.8 GHz excluding the rejected bands from 3.3 to 3.6 GHz and from 4.8 to 6.0 GHz. In addition, the antenna exhibits nearly omni-directional radiation patterns and stable gains over the operating bands.

The broadcast nature of the wireless medium makes the communication over this medium vulnerable to eavesdropping. In this paper, we propose a directional sensitive modulation signal transmitted by Monopulse Cassegrain antenna for physical (PHY) layer security transmission. The main idea is that the sum beam transmit communication signal, simultaneously, and two difference beams transmit artificial noise to guarantee secure transmission of the sum beam. The eavesdropper's channel is degraded by artificial noise, but the desired receiver's channel does not affect because of the spatial orthogonality between the sum beam and two difference beams. In this way, the desired receiver can demodulate the communication signal while the eavesdroppers learn almost nothing about the information from its observations. A closed-form expression of the secrecy capacity is also derived for this practical transmit scheme from the viewpoint of information theoretic. Finally, simulation results show that the proposed signal can significantly improve the performance of secure wireless communications.

A matrix technique for the computation of the per-unit-length internal impedance of radially inhomogeneous cylindrical structures is presented. The cylindrical structure is conceptually divided into a number of layers, each layer being characterized by its constitutive parameters, conductivity, permeability, and permittivity. Within this general framework, compound conductors, compound capacitors, compound magnetic cores, or any other compound structures resulting from a mix of the above, can be analyzed by using the very same tool. The developed software program, MLCS, which implements the mentioned matrix technique, also permits the evaluation of the electric and magnetic fields intensity at the layers' interfaces. The MLCS program is validated by using several application examples.

This paper describes how the ionosphere reflected echoes observed by a high frequency surface wave radar (HFSWR) can be processed to extract information regarding the ionosphere sporadic E (Es) and F2 layers. It is shown that the range/time spectrum contains the data to estimate the occurring time and virtual heights of both the still and drifting Es layer clouds. In addition, for the drifting Es the data can be processed to extract the time-varying ranges and estimate virtual heights, horizontal drifting speeds. Information regarding the F2 layer such as the time-varying virtual heights can also be extracted. The time-frequency distributions (TFD) of the Es and F2 layer echoes calculated after the range migration compensation can be used to extract the intrinsic Doppler patterns. This is further used to obtain information on the internal nonuniform structures and disturbances such as the travelling ionospheric disturbances (TID) that are due to the acoustic gravity waves (AGW). Processing results of echo data collected by the portable HFSWR system named OSMAR-S demonstrate the validness of the above methods.