The dispersion equation governing the guided propagation of TE and TM fast wave modes of a circular cylindrical waveguide loaded by metal vanes positioned symmetrically around the wave-guide axis is derived from the exact solution of a homogeneous boundary value problem for Maxwell's equations. The dispersion equation takes the form of the solvability condition for an infinite system of linear homogeneous algebraic equations.The approximate dispersion equation corresponding to a truncation of the infinite-order coefficient matrix of the infinite system of equations to the coefficient matrix of a finite system of equations of sufficiently high order is solved numerically to obtain the cut-off wave numbers of the various propagating modes. Each cut-off wave number gives rise to a unique dispersion curve in the shape of a hyperbola in the ω-β plane.

A novel dual-broadband circularly polarized folded slot antenna with single-feed is presented. The proposed antenna consists of two folded annular slots. By adjusting the asymmetric widths of the two slots, circularly polarized radiation can be achieved in two different bands. By optimizing the parameters of the proposed antenna, two wide impedance bandwidths of 35.0% (1.91-2.72 GHz) and 46.5% (4.36-7.00 GHz) can be obtained, and two axial ratio bandwidths are 2.36-2.56 GHz and 5.68-6.04 GHz, respectively. The antenna with simple structure is fabricated and measured. Good agreement between the simulated and measured results is also achieved.

A novel cascade microstrip filter with mixed electric and magnetic coupling is proposed and examined. For the first time, we designed a novel multilayer configuration resonator with a compact size. Compared with conventional open-loop filter, the size decreased 75%. First, using novel multilayer configuration resonator instead of monolayer configuration resonator, the size decrease about 45%. Meanwhile, two microstrip patches can be served as inner coupling capacitor, which create and strengthen electric field. Owing to this inner coupling, the size of filter can be further reduced. What's more, with a section of high characteristic impedance transmission line connected to the ground though a via-hole, it can be served as coupling inductor and create main magnetic filed, base on this structure mixed EM coupling is realized, and can generate additional transmission zero. That's means adopt low-order filter can achieve same characteristic as high-order filter. Based on the above solutions, the filter size can be sharply decreased to 12.5 mm×7.7 mm (i.e.,0.05λ_g×0.033λ_g). Furthermore, advantages of using this type filter are not only low insert loss, but also increased attenuation out-of-band with controllable transmission zeros.

This paper presents the theory, design, and experimental investigation of an ultra thin (6% λ₀) and triple band metamaterial radar absorber. The theoretical design of the reported absorber is investigated. The absorber performance was validated using the electromagnetic simulations and confirmed by experimental measurements for different incidence angles. The results confirm that the proposed metamaterial absorber can demonstrate triple bands with better than -15 dB reflection coefficient for all incident angles.

Recent advances in satellite communication technologies in the tropical regions have led to significant increase in the demand for services and applications that require high channel quality for fixed and mobile satellite terminals. Due to lack of reliable investigations regarding accurate performance evaluation, experiments, and analysis on the satellite communication link in tropical regions under atmospheric impairments for both scenarios, accurate signal quality performance analysis is necessary. This paper presents the link characteristics observations and performance analysis with propagation measurements done in tropical region to provide an accurate database regarding rain attenuation in the tropics for fixed and mobile scenarios. The paper also presents a newly developed extension attached to the measurements setup for improved packet error rate (PER) performance evaluation related to the degradations occur in channel quality for different types of impairments (rain, mobility, and physical obstacles) for 4 modulation schemes, namely QPSK, 8-PSK, 16-QAM and 32-QAM. The results show that the rain impairments at Ku band cause up to 12.5 dB and 23 dB at 77.5° and 40.1° elevation angles respectively in two tropical regions inside Malaysia for fixed scenario with a significant increase in PER at higher M-ary modulation schemes. For mobile scenario, the PER appeared at higher M-ary scheme due to the lower signal power degradation in which, in turn, exceeded 1 dB when the vehicle speed exceed 100 km/hr at clear sky. The obstacles at the satellite communication link are shown to have significant effect on the power and PER received by satellite terminal especially at higher M-ary modulation schemes.

To save the computation time and improve the accuracy of reconstruction results by support vector machine (SVM), a multi-output least square SVM (LS-SVM) algorithm is proposed to reconstruct the position of a 2-D perfect electric conductor cylinder below a rough surface. Firstly, the scattered electromagnetic field at a number of observation positions is calculated by the method of moment to generate the training and testing data. Then the multi-output LS-SVM is trained to reconstruct the coordinate of the object center. Numerical results show that this approach is accurate and efficient even with some additive Gaussian noise.

A novel switchable beam textile antenna (SBTA) for wireless body area network (WBAN) applications is proposed. The SBTA is centrally-fed by a coaxial probe and the power distributed over four circular radiating elements. Four RF switches are integrated through which the SBTA is able to generate beam steering in four directions: 0°, 90°, 180°, and 270°, with a maximum directivity of 6.8 dBi at 0°. Its small size (88 mm x 88 mm) and flexibility enables the structure to be easily integrated into safety jackets, rain coats, etc., for tracking, and search and rescue communication purposes. The structure successfully integrates reconfigurability into a wearable textile antenna.

Ramp response technique in low frequency can be used for generating 3-dimensional images of radar targets (even stealthy or buried targets) so as to identify them. This technique uses the target profile function, which is defined as its transverse cross- sectional area versus distance along the observing direction. For mutually orthogonal observing views, reconstructed 3D images are quite accurate. However, in practice, due to the bias introduced from the response in shadow region and from limited non-orthogonal observing directions, reconstructions become distorted.To evaluate the quality of the reconstruction and to further identify objects from their reconstruction, we need to calculate profile functions of 3D reconstructed objects in arbitrary directions. Therefore, in this paper, we propose an algorithm meeting this needs.

In this paper, a novel second-order transmission condition is developed in the framework of non-conformal finite element domain decomposition method to meet the challenges brought by complex and large-scale electromagnetic modeling. First, it is implemented efficiently on the non-conformal interface via a Gauss integral scheme. Then, the eigenvalue analysis of the DDM system show a more clustered eigenvalue distribution of this transmission condition compared with several existing transmission conditions. After that, it is applied to large-scale complex problems such as S-type waveguides in the high frequency band and dielectric well-logging applications in the low frequency band. The final numerical results demonstrate that this transmission condition has high efficiency and huge capability for modeling large-scale problems with multi-resolution in any frequency band.

In this paper, two staggered array configurations are presented for enhancing size and radiation properties of wideband phased array systems. The proposed arrays are obtained either by rotating each element 45° or by inserting additional rows in the middle which are shifted by half the distance between elements. These two configurations allow for a smaller distance between array elements (29% less), while the actual distance between elements in the diagonal direction is kept the same. Reducing the distance between elements results in eliminating/reducing the grating lobes in a wider frequency range, which improves the array usable bandwidth. In addition, this proposed array produces better gain and maximum steering angle.

This paper addresses the possibility of displacement measurement by microwave interferometry at an unknown reflection coefficient with the use of as few as two probes. The case of an arbitrary interpobe distance is considered. The measurement error as a function of the interprobe distance is analyzed with the inclusion of variations of the detector currents from their theoretical values. The analysis has shown that as the interprobe distance decreases, the maximum measurement error passes through a minimum for reflection coefficients close to unity and increases monotonically for smaller reflection coefficients. Based on the results of the analysis, the interprobe distance is suggested to be one tenth of the guided operating wavelength λ_g. In comparison with the conventional interprobe distance of λ_g/8, the suggested one offers a marked reduction in the maximum measurement error for reflection coefficients close to unity, while for smaller ones this error remains much the same (for a detector current error of 3%, the maximum measurement error in percent of the operating wavelength is 2.2% and 1.0% at λ_g/10 as against 4.8% and 2.7% at λ_g/8 for a reflection coefficient of 1 and 0.9, respectively, and 2.9% at λ_g/10 as against 2.4% at λ_g/8 for a reflection coefficient of 0.1).

The fine-grained parallel micro-genetic algorithm (FGPMGA) is developed to solve antenna design problems. The synthesis of uniformly exited unequally spaced array is presented. Comparison with the micro-genetic algorithm (MGA) has been carried out. It is seen that the FGPMGA significantly outperforms MGA, in terms of both the convergence rate and exploration ability. The FGPMGA can also reduce the optimization time. Then the FGPMGA and the body of revolution finite-difference time-domain (BOR-FDTD) are combined to achieve an automated design process for conical corrugated-horn antenna. Numerical simulation results show that the horn antenna has good impedance matching (the VSWR is less than 1.5), stable beamwidth and gain, as well as good rotation symmetry patterns over the whole band 8~13 GHz.

A compact quad-band hybrid antenna for Compass/WiMAX/WLAN applications is proposed. The hybrid antenna is designed based on the method of combining a composite right/left-handed transmission line (CRLH-TL) unit cell with a meandered monopole and wide multi-band characteristics are achieved by merging some of resonance frequencies of the CRLH-TL unit cell and meandered monopole together. Coplanar waveguide (CPW) is used as a parallel excitation for both the CRLH-TL unit cell and meandered monopole. A prototype of the proposed hybrid antenna has been constructed and experimentally studied. The measured results show that four distinct operating bandwidths with 10 dB return loss are about 30 MHz (1.25-1.28 GHz), 290 MHz (2.44-2.73 GHz), 650 MHz (3.17-3.82 GHz) and 1130 MHz (5.03-6.16 GHz), covering the Compass B3, 2.5/3.5/5.5 GHz WiMAX and 5.2/5.8 GHz WLAN bands. Furthermore, the antenna has a single-layer planar structure with a small volume of only 31 × 21 × 2 mm³. Acceptable radiation patterns and peak realized gains are obtained over the operating bands.

In this paper, we present a low-profile, compact, ultra-wideband antenna that uses a set of closely coupled radiators. The system of two coupled radiators has two different linearly independent modes of operation with complementary frequency bands of operation. These include the differential mode and the common mode of operation. When the antenna is excited in the common mode of operation, it acts as an ultra-wideband (UWB) antenna covering a broad frequency band. When excited in the differential mode, the antenna operates as a wideband dipole in a frequency range below that of the common mode. Thus, by appropriately combining the two modes using a suitably designed feed network, the bandwidth of the antenna can be extended and its lowest frequency of operation is reduced. Mode combining is achieved with a feed network that employs a frequency-dependent phase shifter. Using this feed network, the two modes of the antenna are combined and a single-port broadband device is achieved that has a bandwidth larger than that of either the common or the differential mode individually. A prototype of the antenna is fabricated and experimentally characterized.

In this paper, the design of an array of wideband combined antenna elements is presented. A TEM horn antenna is combined with magnetic dipoles to obtain a wideband element with a bandwidth from 180 MHz to 30 GHz. The element is then miniaturized in order to be placed in a two by two array, and then the optimized values of the horizontal and vertical spacings are calculated. To enhance the array bandwidth, a lens is placed in front of each element. This leads to an increase in the bandwidth from 0.2 to 10 GHz while no grating lobes appear over the bandwidth. The combined element is fabricated and the simulation results are verified by the measured data. Furthermore, simulation results for the return loss, radiation patterns and antenna gain for the 2 × 2 array are presented.

Spherical shells are proposed and presented to improve the gain of a class of wideband phased array systems. This kind of phased arrays is composed of compact elements, which allow for a small distance between elements that is much less than half wavelength at lower operating frequencies. This small distance, as a function of wavelength, results in a small gain. Therefore, shells confronting the array are proposed to improve the gain. The formulations required to define the geometry and material properties of the shell are developed. Two and four element arrays are designed and simulated with and without shells to test the technique, and promising results are obtained at lower frequencies for the array with shells.

In this paper, an experimental characterization of a MIMO underground channel is presented. A simple statistical model is proposed at 2.45 GHz. The Channel is characterized in terms of path loss, shadowing, RMS delay spread, and capacity. The measurements are carried out in an underground mine, which is a harsh confined environment. The path loss model is extracted from measured data for the line of sight (LOS) and non line of sight (NLOS) scenarios for both MIMO and SISO channels. The path loss exponent in LOS is less than 2 in MIMO and SISO as the environment has a dense concentration of scatterers. A statistical study is carried out to find the delay spread. For MIMO and SISO, there is no relation between the delay spread and the transmitter receiver distance. Furthermore, the delay spread of the MIMO is less than the one of the SISO channel in the LOS measurement campaigns. Aikake information Criteria are used as a goodness of fit for different statistical distributions to represent the delay spread. According to the calculated capacity for a constant signal to noise ratio in LOS case, the transmission performance is significantly improved by using the MIMO scheme over the traditional SISO. Therefore, MIMO is an ideal candidate for future wireless underground communications.

This paper is concerned with the theory of wave propagation in biaxial anisotropic media. Consider a multilayered planar structure composed of media with electric and magnetic anisotropy, surrounded by two half spaces. Exat relations for reflection coefficient from this structure can be useful for arriving at the intended applications. In this paper, by matching of transverse field components at the bounderies, we will arrive at exact recursive relations for reflection coefficient of the structure. In the previous works, the magnetic and electric anisotropy were not taken into consideration at the same time, or complex relations were arrived. But using this novel method, those complexities will not appear and both electric and magnetic anisotropy are take into consideration. Moreover, we will not set any limits on the right half-space so the right most half-space may be a PEC, PMC, PEMC, surface impedance, dielectric or a metamaterial. Finally, the last section of the paper confirms the validity of the relations arrived at and as an interesting application; the zero reflection condition will be obtained.

A WLAN band notched compact ultra-wideband (UWB) microstrip monopole antenna with stepped geometry is proposed. A L-slot loaded modified mushroom type Electromagnetic Band Gap (EBG) is designed, analyzed and used to realize notched band characteristics for wireless local area network (WLAN) in the UWB frequency range. The proposed antenna having partial ground plane is fabricated on a low cost FR4 substrate having dimensions 40 ( Lsub ) × 30 (Wsub ) × 1.6 (h) mm³ and is fed by a 50-Ω microstrip line. The results show that the proposed antenna achieves impedance bandwidth (VSWR < 2) from 2.3 GHz to 11.4 GHz with band notched characteristics (VSWR > 2) from 4.9 GHz to 6 GHz. Fidelity factor for proposed antenna is also analyzed to characterize time domain behavior. Simulation and measurement results of VSWR are found in good agreement.

A miniaturized crossed-dipole fractal antenna with circular polarization is presented in this letter. The radiating elements of the antenna were built as the Koch curve, and the antenna was mounted on a specially designed ground plane. Furthermore, the influence of fractal dimension to bandwidth and axial ratio of fractal antenna is also experimentally studied. The bandwidth of the VSWR≤ 1.5:1 within 3dB axial ratio for the fractal antenna is about 5.98%. The measured results show that the proposed fractal antennas have good circular polarization property, efficiency and 23.4-33.5% size reduction comparing with the conventional crossed-dipole antenna. The tested results are in good agreement with that of the simulations.