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.

In the domain of electromagnetic wave propagation in the presence of rough surfaces, the Rayleigh roughness criterion is a widely-used means to estimate the degree of roughness of considered surface. In this paper, this Rayleigh roughness criterion is extended to the case of rough layers. Thus, it provides an interesting qualitative tool for estimating the degree of electromagnetic roughness of rough layers.

With the growth of broadband wireless technology like code division multiple access (CDMA) and ultra-wideband (UWB), lots of development and efforts towards wireless communication system and imaging radar system are well justified. Efforts are also being imparted towards a convergence technology involving both communication and radar technology which will result in intelligent transport system (ITS) and other applications. The authors have tried to converge the communication technologies towards radar and to achieve the interference free and clutter free quality remote images of targets using DS-UWB wireless technology. In this paper, we propose a direct sequence spread spectrum (DSSS) radar for remote sensing in ITS system. We have successfully detected single target using 1D radar imaging, and also separated multiple targets and implemented DSSS radar using software defined radio (SDR) to get continuous connectivity of the system. Authors have sought down the limitations of DSSS radar which according to them can be solved by using adaptive equalizer and rake processing.

A thin dipole antenna is a well-known antenna with linearly polarized wave operation. In this work, a wide-strip dipole antenna is proposed for circularly polarized wave operations. To obtain circularly polarized (CP) wave operations, there are two conditions to be satisfied. One is that the antenna must have two degenerated orthogonal modes with different resonant frequencies. The other is that the phase difference of two orthogonal modes is 90 degrees. To match the first condition, the slab width W is tuned to generate current distributions directed in two different directions. In addition, the second condition is matched by asymmetric feeding point by adjusting the overlapped square width C. The parametric study is completed by the Ansoft HFSS simulator. Simulated results reveal that the CP wave is mainly influenced by the slab width W. The influences of the parameters C and d on the performances of the proposed antenna are also investigated in this paper. Taking -8 dB as reference, there are two working bands for this proposed antenna and the measured center frequencies are 0.66 GHz and 2.04 GHz, respectively, and the corresponding bandwidths are 0.27 GHz (40%) and 1.78 GHz (87%), respectively. In addition, the measured center frequencies and bandwidths of the axial ratio are 1.94 GHz and 0.53 GHz (27%), respectively.

In this paper, a new hybrid method of obtaining the degrees of freedom for redial airgap length in Switched Reluctance Motor operation under normal and faulty conditions based on magnetiostatic analysis is presented. At the beginning, this method goes through the magnetic design of the motor utilizing three dimensional (3-D) Finite Element Method (FEM) in order to consider the end effects as well as axial fringing field effects. The motor parameters, such as torque, flux linkage, flux density versus rotor position are precisely obtained. Then, a Multi Layered Perceptron Neural Network is designed by considering the nonlinear behavior of the motor parameters obtained under different modes of operatin. Using this network and the obtained parameters from FEM, an Objective Function (OF) for torque ripple with the aim of having a minimum mean square error is estimated. In addition, an improved Genetic Algorithm (GA) for the minimization the OF is also presented to determine the motor's operational regions. Finally, the legal intervals for different modes of motor operation are addressed.

This paper presents an analysis of found results in experiments developed with transformers built with planar coils, when they are excited by square waves, in comparison with transformers built with planar coils inner ring coils. The transformer was built joining two planar coils one over the other. In this kind of transformer, similar responses as analysis of transformers built with planar coil inner ring coil are found, as well the results of resonance. Because the low self-inductances and parasitic capacitances obtained in these configurations, although the coils resistance is low, which generates low exponential drops on responses. The resonance is found in higher frequencies, but satisfying conditions of sum of responses in resonance.

In 1-D photonic crystal with structural defects, localized mode results in strong electromagnetic fields around the position of the defect. Thus, the strong fields enhance the tangential force on a lossy dielectric layer, as well as normal force on the perfect dielectric slab. The results of this study suggest a class of micro-machines driven by electromagnetic wave, such as sunlight or microwave.

The fade margins for 15, 23, 26 and 38 GHz frequency bands are predicted based on one-minute rain rate measurements for four years at Universiti Teknologi Malaysia (UTM) Skudai and the specifications of the given four MINI-LINKS. The availabilities of terrestrial microwave links are also investigated based on rain attenuation data collected from seven operational microwave links at 15 GHz and one at 23 GHz for more than one year. The fade margins for all eight links are measured based on the rain attenuation data collected with different hop lengths. In this paper, the feasibility to design outage-free wireless broadband radio link also highlighted. These results will contribute to the better design of outage-free Broadband Fixed Wireless Access (BFWA) system such as, Local Multipoint Distribution Service (LMDS) and IEEE802.16 in tropical regions.

We investigate the problem of defining propagating constants and modes in metallic waveguides of an arbitrary cross section, filled with a homogeneous bi-isotropic material. The approach follows the guidelines of the classical theory for the isotropic, homogeneous, lossless waveguide: starting with the Maxwell system, we formulate a spectral problem where the square of the propagation constant shows up as the eigenvalue and the corresponding mode as the eigenvector. The difficulty that arises, and this is a feature of chirality, is that the eigenvalue is involved in the boundary conditions. The main result is that the problem is solvable whenever the Dirichlet problem for the Helmholtz equation in the cross section is solvable and a technical hypothesis is fulfilled. Our method, inspired by the null-field method, is quite general and has a good potential to work in various geometries.

The thermal noise of the resistive vee dipole (RVD) has been analyzed using a numerical model based on the method of moments. The RVD analyzed in this paper has curved arms and is loaded with surface-mount chip resistors, which approximate a modified Wu-King profile. The total noise power delivered to a 200­­­­ Ω feed line and the contribution of individual resistors to the total noise power are presented. The results show that the noise temperature of the RVD is very high and the resistors close to the drive point contribute more to the total noise power than do the resistors close to the open ends of the antenna arms.

This paper addresses the problem of direction of arrival and time delay estimation, and derives multi-invariance MUSIC (MI-MUSIC) algorithm therein. The proposed MI-MUSIC, which only requires one-dimension searching, can avoid the high computational cost within two-dimension MUSIC (2D-MUSIC) algorithm. It means that MI-MUSIC algorithm has better performance than that of ESPRIT and MUSIC, and also can be viewed as a generalization of MUSIC. Simulation results verify the usefulness of our algorithm.