In this paper, we present a new class of miniaturized microstrip bandpass filters with low-insertion loss, sharp-rejection and narrow-band performance. The proposed filters are composed of two spiral-shaped resonators and rectangle window feed structures. Both back-to-back and interdigital combinations of the resonators are adopted to obtain the miniaturized filter size. Compared to the traditional square loop bandpass filter, the sizes are reduced by 82% and 80%. It is also found that there is a pair of transmission zeros located on each side of the passbands, resulting in high selectivity. To validate the proposed idea, two demonstration filters with back-to-back and interdigital spiral-shaped resonators are implemented. The measured results exhibit good agreement with the full-wave simulation results.

Electrical Capacitance Tomography (ECT) is a non-invasive and non-destructive imaging technique that uses electrical capacitance measurements at the periphery of an object to generate map of dielectric permittivity of the object. This visualization method is a relatively mature industrial process tomography technique, especially in 2D imaging mode. Volumetric ECT is a new method that poses major computational challenges in image reconstruction and new challenges in sensor design. This paper shows a nonlinear image reconstruction method for 3D ECT based on a validated forward model. The method is based on the finite element approximation for the complete sensor model and the solution of the inverse problem with nonlinear iterative reconstruction. The nonlinear algorithm has been tested against some complicated experimental test cases, and it has been demonstrated that by using an improved forward model and nonlinear inversion method, very complex shaped samples can be reconstructed. The reconstruction of very complex geometry with objects in the shape of letters H, A, L and T is extremely promising for the applications of 3D ECT.

In this paper, the design of Log Periodic Fractal Koch Antennas (LPFKA) is proposed for Ultra High Frequency (UHF) band applications. The procedure to design the LPFKA with three different numbers of iterations in order to reduce the antenna size is discussed. The Computer Simulation Technology (CST) software has been used to analyze the performances of the designed antennas such as return loss, radiation patterns, current distribution and gain. The antennas have been fabricated using FR4 laminate board with wet etching technique. Using fractal Koch technique, the size of the antenna can be reduced up to 27% when the series iteration is applied to the antennas without degrading the overall performances. Both simulated and measured results are compared, analyzed and presented in this paper.

The problem about the electrical current distribution along thin radial impedance monopole, located on the perfectly conducting sphere, has been solved in a rigorous electrodynamic formulation in the paper. The problem formulation strictness is provided by the use of the Green's function for the Hertz's vector potential for unbounded space outside the perfectly conducting sphere at formulation of the initial integral equation concerning the current in monopole. The approximate analytical solution of the integral equation has been obtained by the method of iterations both for the case of excitation of the monopole by the δ-generator of voltage, located on the finite distance over the spherical scatterer, and at the excitation of the monopole at its basis.

With deregulation of telecom sector (law 24/96) in our country (Morocco), many operators of cellular network appear. Among the operators technology that operate, we find GSM9800 and CDMA900 that are used by two different operators. It turns out from the measurements of indicator of quality of service that the performance of GSM900 is degraded, and the major cause is the interference created by CDM800 which cannot be neglected. In this paper, we adopt a new approach in order to make GSM900 and CDMA800 operate in harmony. This method is based on a physical optimization of antenna systems and could be understood as a physical symmetry rotation in the space of parameters such that tilt and Azmit control the system. It independently reduces the interference effects on the distance between the base stations. Moreover, it allows us to improve client service without using hard installations and inexpensive technologies.

In this paper, a dual-loop gate antenna is designed to generate the magnetic field distribution in various directions. It is applied to Radio Frequency Identification (RFID) systems for animal identification operating at the low frequency (LF) band of 125 kHz and 134.2 kHz. The percentage of volume of magnetic field intensity is introduced and used as a figure of merit in the design. The optimum antenna parameters are also designed by the genetic algorithm (GA) in conjunction with the Numerical Electromagnetic Code (NEC). The prototype antenna was fabricated and tested to confirm the antenna performance in the LF-RFID system for animal identification. It is found that the dual-loop gate antenna can be efficiently used in the LF-RFID system.

A novel complementary split ring resonators (CSRR) is applied to realize a compact Ultra-Wide Band (UWB) bandpass filter based on half-mode substrate integrated waveguide (HMSIW) in this paper. Sharpened rejection skirts and widened upper stopband are achieved due to the two resonant frequencies of the proposed CSRR. Very good agreement is observed between measurement and simulation results.

Numerical results are presented for single-mode guidance, which is based on photonic band gap (PBG) effect, in one-dimensional planar all-dielectric light-guiding systems. In such systems there may be two kinds of light-speed point (the intersection of a mode-dispersion curve and the light line of guiding region ambient medium): One is the intrinsic light-speed point that is independent of the guiding region width, and the other is the movable light-speed point that varies with the guiding region width. It is found that the intrinsic light-speed point plays an important role to form the single-mode regime by destroying the coexistence of the lowest guided TM and TE modes that are born with a degeneration point. A mode-lost phenomenon is exposed and this phenomenon suggests a way of how to identify PBG-guided fundamental modes. Quasi-cutofffree index-guided modes in the PBG guiding structures are examined, which appear when the higher-index layers are adjacent to the guiding region and the guiding region width is small. The transverse resonance condition is derived in the Maxwell optics frame, and it is shown that there is a significant revision to the traditional one in the ray optics model. A sufficient and necessary condition for intrinsic light-speed points is given, which provides strong support to the numerical results.

This paper proposes the configuration of a novel dual-polarized wide-band patch antenna system suitable for indoor mobile communication applications. This configuration consists of two compact patch antennas, which have different feed structures from classical patch antenna configuration. These antennas, which are separated by a thin absorber to have a good isolation, are fed independently to obtain dual polarization. The antenna structure is designed, simulated, manufactured and measured. The operation bandwidth spans 1900-2700 MHz covering Bluetooth, Wireless Local Area Networks (WLAN) and Universal Mobile Telecommunications System (UMTS) bands. The simulations show good agreement with the measurement results that the antennas have return losses higher 15 dB, and the coupling between two antennas is below -20 dB within the operation band.

In this paper, an innovative technique for the determination of the dielectric properties of planar substrates is presented. Starting from a set of impedance measurements performed on a section of a microstrip transmission line built on the planar dielectric substrate under test, the proposed technique formulates the reconstruction problem in terms of an optimization one successively solved by means of an effective stochastic algorithm. Such a method allows one the reconstruction of the permittivity values at multiple frequencies by simply using a vector network analyzer and a standard calibration procedure for the impedance measurement. The results of some representative experimental tests are shown for a preliminary assessment of the effectiveness of the proposed approach.

A novel circularly polarized microstrip rectenna operating on C-band with low profile is proposed. The input and output match networks of the rectifying circuit are realized by λ/4 microstrip lines and open stubs with the harmonics being inhibited. The circularly polarized receiving antenna is a truncated-corner square patch fed by microstrip line with DGS (Defect Ground Structure) for suppressing high order harmonics further. The voltage of 4.34V on the load of 298 Ω is measured and the overall RF-DC conversion efficiency of 68.4% is obtained. This kind of rectenna can be extended to large arrays for wireless power transmission applications.

A novel design of multiband microstrip antenna array with dumbbell shape defected ground structure (DGS) is presented. The DGS is inserted into the ground plane between the two elements of the antenna array in order to suppress mutual coupling. Both simulation and measurement results verified that the DGS had improved the radiation properties of the antenna array. Measurement results of the DGS antenna showed mutual coupling reduction of maximum 5 dB and gain enhancement to 3 dB.

In this paper, a broadband quadrature hybrid is presented. The hybrid comprises a Wilkinson divider, followed by an improved Schiffman phase shifter. An improved wideband Schiffman phase shifter on a single layer printed circuit board is accompanied by a lumped capacitor between two coupled lines. Lumped capacitor is in parallel with the odd-mode capacitance of the two coupled lines, hence, the odd-mode capacitance is increased and consequently the odd-mode impedance is decreased. Therefore, by this method we can control the ratio of the even mode impedance to the odd mode impedance which is critical in Schiffman phase shifter design. Compared with the cascading Microstrip multi-section coupled lines, our proposed single layer phase shifter is smaller in size. Also, the proposed phase shifter has the greater bandwidth compared to the patterned ground plane Schiffman phase shifter and its realization is simpler because of its single layer structure. As an example, a Schiffman phase shifter at frequency f₀ =650 MHz is designed and simulated. With the proposed phase shifter a 90°hybrid is designed, simulated, fabricated and measured. Exprimental results show that the amplitude and phase imbalance between two paths at worth case are within 0.75 dB and 5°, respectively, over the frequency band from 362 MHz to 891 MHz, or around 84% bandwidth. The measured return loss is better than -10.8 dB over the operating frequency band.

A modified two-element Yagi-Uda antenna with tunable beams in the H-plane (including four significant beams: forward, backward, omni-directional, and bi-directional beams) is presented. These tunable beams are achieved by simply adjusting the short-circuit position of the transmission line connected to the parasitic element. The principle of operation is investigated by examining the current relations between the driven and parasitic elements. Measured results of a fabricated prototype are presented and discussed.

In this paper, the design of compact and high performance parallel coupled line wideband bandpass filter using image parameter method are proposed. The filter mainly comprising one-stage parallel coupled line and two open stubs are designed and implemented on commercial RT/Duroid 5880 substrate. The equivalent circuit of the proposed structure is initially derived by using the image parameter method. It is found that, the normalized bandwidth (NBW) of image impedance for the one-stage parallel coupled line has a relation to the electromagnetic (EM) simulated bandwidth. To further improve the selectivity, two open stubs are connected near the input/output (I/O) ports. The design procedures and their limitations are discussed in detail. The proposed filters are fabricated, measured and showing good characteristics of 87% fractional bandwidth as well as good insertion/return loss, flat group delay varies between 0.3-1.5 ns. High passband selectivity and wide stopband from 8-14 GHz are obseved. The measured results are also having a good agreement with the simulated results.

The main aim of this paper is to accentuate the sensitivity of correlation length 'l' as an important roughness parameter in quantifying the moisture content of bare soil surfaces with specular scattering. For this purpose, an indigenously designed bistatic scatterometer has been used to generate co-polarized specular data at X-band (10 GHz) with incidence angle varied from 30°-- 70°in steps of 10 degrees. The moisture and roughness conditions of the bare soil surface were changed under controlled conditions. Twenty seven experimental fields specified on the ground of different roughness and moisture conditions have been analyzed. Higher level of moisture content with larger correlation lengths was found to be more suitable for observing the effect of increasing rms height on specular scattering. Kirchhoff approach (KA) considered under the stationary phase approximation (SPA) has been used as an inversion algorithm with the application of genetic algorithm for the retrieval of soil parameters. A good agreement was observed between the experimental and retrieved values of soil moisture content (m_ν) and roughness parameters (s and l).

Reconstruction of perfectly electric conductors (PEC) with transverse magnetic (TM) illumination by a subspace-based optimization method (SOM) is presented. Apart from the information that the unknown object is PEC, no other prior information such as the number of the objects, the approximate locations or the centers is needed. The whole domain is discretized into segments of current lines. Scatterers of arbitrary number and arbitrary shapes are represented by a binary vector, and the descent method is used to solve the discrete optimization problem. Several numerical simulations are chosen to validate the proposed method. In particular, a combination of a line type object and a rectangular shape object is successfully reconstructed. The subspace-based optimization method for PEC scatterers is found to be more complex than its counterpart for dielectric scatterers.

In this paper, accurate synthesis formulas obtained by using a differential evolution (DE) algorithm for conductor-backed coplanar waveguides (CBCPWs) are presented. The synthesis formulas are useful to microwave engineers for accurately calculating the physical dimensions of CBCPWs. The results of the synthesis formulas are compared with the theoretical and experimental results available in the literature. A full-wave electromagnetic simulator IE3D and experimental results are obtained in this work. The average percentage error of the synthesis formulas obtained by using DE algorithm is computed as 0.67% for 1086 CBCPW samples having different electrical parameters and physical dimensions, as compared with the results of quasi-static analysis.

Recently the Bacterial foraging optimization algorithm (BFA) has attracted a lot of attention as a high-performance optimizer. This paper presents a hybrid approach involving Bacterial Swarm Optimization (BSO) and Nelder-Mead (NM) algorithm. The proposed algorithm is used to design a bow-tie antenna for 2.45 GHz Radio Frequency Identification (RFID) readers. The antenna is analyzed completely using Method of Moments (MoM), then the MoM code is coupled with the BSO-NM algorithm to optimize the antenna. The simulated antenna and the optimization algorithm programs were implemented using MATLAB version 7.4. To verify the validity of numerical simulations, the results are compared with those obtained using Feko Software Suite 5.3.

The method of least squares (MLS) is used to develop an algorithm for the optimum design of any type of filter under any design specifications for the realization of lowpass, bandpass, highpass and bandstop characteristics. The proposed filter design method can be used for any general filter network topology, which provides high flexibility for the selection of circuit configurations suitable for any desired application. The MLS filter design procedure also incorporates source and load impedance matching, which eventually leads to the simplicity of circuits. The proposed method of filter design may be used for lowpass prototype filters or directly for bandpass, highpass or bandpass filters. Several examples of MLS filter designs are given, which compare very well with the classical methods and indicate the advantages of the proposed method of filter design. The MLS filter design may realize any frequency response characteristics, such as spurious response elimination, multiband filter realization and enhancement of some desired behaviors.