εThis paper presents an analytical solution to study the reflection and transmission of an electromagnetic wave impinged upon a multilayered structure. The structure is composed of a fractal slab sandwiched by ordinary material on either side. Modified Maxwell equations for fractional dimension space are used to represent the fields in a fractal slab. The electromagnetic characteristics of the structure are studied for different dimensions (D) and numerical results are presented for both the classical (D is integer) and fractal (D is non-integer) slabs. This study provides foundations for investigating the waveguides filled with fractal media and electromagnetic waves propagation in multilayered structures at fractional boundaries.

In this paper, the problem of RCS reduction in cylindrical structures with various boundary conditions are investigated comprehensively. It has been done through a general form of boundary conditions called Mixed-Impedance boundary conditions. Genetic algorithm, a powerful optimization method, is used to explore specific conditions that provide major reduction of cylindrical structure's RCS. The optimizations are performed in case of normally and obliquely incident illuminations. Finally, the optimized values are formulated in terms of incident angle to construct a simple and fast way of evaluation of the minimum RCS situation. The results are compared with a cylindrical PEC structure, and it has been verified that the optimized values of MI boundary conditions could result in significant backward RCS reduction for both normal and oblique incident.

A novel microstrip bandpass filter with four transmission zeros is proposed. Four transmission zeros close to the passband are realized to improve the selectivity for the passband. A sixth-order passband is realized with two shorted stubs and a dual-mode ring resonator. The transmission zeros near the passband can be adjusted conveniently by only changing the characteristic impedances of the coupled lines. For demonstration, a planar bandpass filter (3-dB bandwidth 21.9%) was designed and fabricated.

A novel log-periodic dipole antenna for dual-polarized radar systems is presented. The proposed antenna employs meander line technology and matched loads. The simulated and measured results show that the -6 dB reflection coefficient bandwidth of the dual-polarized antenna covers the desired band of 2-8 GHz and the port isolation is higher than 32 dB, along with -20 dB cross-polarization discrimination for both E- and H-planes.

This paper presents the transmission line analysis, thermal and structural analysis of a multi-section coaxial coupler (MSCC) used in traveling-wave tubes (TWTs) to handle high average power over a wide frequency range. Power transmission through coupler from the device demands very good matching between load and source impedances such that low VSWR is achieved. Modeling of the MSCC for wideband TWTs in commercially software packages takes very long iteration time even in high-end computers. An analytical approach has been developed to model MSCC which takes less iteration time even in ordinary computer. Analytical results have been compared to those obtained from CST microwave studio. Finally, thermal and structural analysis has been carried out to study the thermal aspects for handling high average RF power.

A compact microstrip notched ultrawideband patch antenna (UWB) with inverted E- and F-shaped slots is presented. By introducing a new inverted E-shaped notch in the radiating plane, band-notch about 2.68 to 3.55 GHz is achieved. A new type of Defected Ground Structure (DGS) in the ground plane is employed to extend the lower limit of the bandwidth so as to cover ISM 2.4 GHz WLAN-frequency band. The proposed antenna offers 126% bandwidth overall dimension of 13×17×1.6 mm³. The experiment results indicate that the proposed antenna can meet the requirement for UWB communication with size miniaturization.

A systematic procedure is presented for synthesis of generalized Chebyshev lossy bandstop filters with nonparaconjugate transmission zeros. From a lossy scattering parameters with the prescribed reflection zeros, the transformation formulas from the scattering matrix to the admittance matrix are obtained by reconstructing the non paraconjugate transmission zeros as paraconjugate ones. The canonical transversal array is modeled by partial fraction expansion of the normalized admittance functions, resulting in an increased order of the final network provided there are nonparaconjugate transmission zeros. The methods are simpler and more general than the ones in the literature. So it shows great versatility, and can also accommodate lossless network or a transfer function with symmetrical transmission zeros. To illustrate the proposed synthesis procedure, three typical examples have been carried out to validate the synthesis method.

General dispersion equation is obtained at arbitrary inclination angles of the external magnetic field and wave vector of an incident EM wave. Statistical characteristics of the phase fluctuations of scattered high frequency EM waves in the collision magnetized plasma caused by electron density and external magnetic field fluctuations taking into account polarization coefficients for both ordinary and extraordinary waves are calculated analytically. The influence of collision frequency, anisotropy factor and angle of inclination of prolate irregularities of electron density fluctuations with respect to the geomagnetic field of lines on the broadening of the spatial power spectrum is analyzed. Phase portraits of the phase fluctuations caused by the geomagnetic field fluctuations are constructedat different spatial parameters characterizing magnetic field and electron density fluctuations. Numerical calculations are carried out for the ionospheric F-region parameters using experimental data.

A novel technique for extrapolation of transient response using early-time and low-frequency data is proposed in this paper. An improved extrapolation scheme using approximate prolate series is presented to obtain a transient electromagnetic response. The approximate prolate series, which has an approximately band-limited and sub-domain nature, is a better choice for extrapolating the time-domain electromagnetic response than orthogonal polynomials, such as Laguerre functions and Hermite functions. A novel regularization method based on truncated generalized SVD is also proposed to solve the ill-posed extrapolation problems, which make the extrapolation technique much less sensitive to noise in the known part of the response. Some numerical results are presented to illustrate the effectiveness and accuracy of the proposed method in extrapolation of transient electromagnetic problems.

An effective technique utilizing neutralization lines to increase the isolation of a compact two-element dual-frequency microstrip antenna array is proposed in this paper. Two neutralization lines connect the two elements at the edge of each radiating patch. The positions and lengths of the two neutralization lines are studied to get the best performance of element isolation. A prototype of the proposed design was fabricated to validate the results. The measured results agree well with the simulated ones. It is shown that an increase of about 25 dB at the lower frequency and that of 17 dB at the upper frequency in isolation between the two antennas have been achieved.

This paper proposes a hybrid multichannel processing method for spaceborne Hybrid Phased-MIMO SAR (HPMSAR) that can achieve different applications of multi-direction swath imaging on the same platform. The method is optimal because it is a combination of two-dimension (2-D) advanced digital beamforming (DBF) technology and multichannel pre-filter technology for high-resolution wide-swath SAR signal processing. Multichannel signal processing technology for future spaceborne SAR will no longer be single and this combination may be the best choice. The proposed method could avoid spectrum aliasing caused by low pulse repetition frequency (PRF), separate the overlapped echoes caused by different subpulses corresponding to multi-direction swathes and remove the range ambiguity and azimuth ambiguity deeply. At first, we build the signal model of HPMSAR system. Furthermore, the pre-filter design is presented by using matrix inversion method. Then, we address different methods applied to 2-D DBF and propose the advanced linearly constrained minimum variance (LCMV) method. Image results on simulated distributed targets validate the proposed hybrid multichannel processing method.

This paper presents a new implementation technique of transmission zeros in an in-line coupled filter. Neither cross couplings between non-adjacent resonators nor separate side-line resonators have been used. Instead a mixture of single-mode hairpin resonators and dual-mode patch resonators have been adopted in a bandpass filter with one asymmetric transmission zero. The introduction of the patch led to an improved frequency selectivity through an independently controllable transmission zero. This approach has been verified by a three-pole filter at 2.6 GHz with 8% bandwidth and a transmission zero at 2.4 GHz. Good agreement has been shown between the measurements and the simulation.

In this article, a novel printed quasi-self-complementary antenna with tri-band characteristic is presented for WLAN and WiMAX applications. A triangular quasi-self-complementary structure, which consists of a radiating patch and its counterpart slot on the ground, is employed to produce two operating bands centered at about 2.5 and 5.2 GHz. Then, by introducing a rectangular slit cut from the patch and its complementary mirror image strip inserted into the slot, an additional resonance at 3.5 GHz is excited and tri-band operation can be realized. A prototype of the proposed antenna has been successfully fabricated and measured. Both the simulated and measured results are obtained to demonstrate the promising performance required for practical applications. Based on the results, it is shown that 10-dB impedance bandwidths of the proposed antenna are 510 MHz (2.25-2.76 GHz), 330 MHz (3.38-3.71 GHz), and 770 MHz (5.1-5.87 GHz), respectively. Also, nearly omnidirectional radiation patterns and acceptable antenna gains can be achieved over the three operating bands.

The success of a ground penetrating radar (GPR) signal modeling scheme largely depends on its accuracy and computational efficiency. Most of the modeling schemes suffer from inaccuracy because of unrealistic assumptions of complex GPR environment. In this respect full wave model (FWM) of GPR signal is a promising approach for accurate characterization of multi-layered media. However, large computation time of FWM compared to other simplified models makes the approach inefficient for real time application. In this work an FWM scheme is developed based on electric field equivalent magnetic current density at antenna phase center. The compact analytical expression of Green's function representing response due to layered media is derived. Then a plane wave model (PWM) is proposed by introducing a spreading factor based on simplified expression of the FWM. The model inversion is successfuly carried out by a gradient based algorithm. A stepped frequency continuous wave GPR in off-ground monostatic configuration is implemented in laboratory environment to verify performances of the models. Experimental analysis proves that the proposed PWM is as accurate as FWM, and its computation efficiency is enormous to detect layered media parameters.

Solutions of Maxwell's equations for electromagnetic fields inside a waveguide coated with chiral nihility metamaterial and having one axis fractal are presented in this paper. A two-dimensional line source placed at the center of the waveguide is taken as an excitation. Power of electromagnetic fields inside the waveguide is determined, and results are plotted for various fractal dimension values ranging from 1 < D ≤ 2, and thickness of the chiral nihility coating.

A hepta-band covering GSM850/900/1800/1900/ UMTS/LTE2300/LTE2500 handset antenna array is presented. The antenna array consists of two symmetric antenna elements, A T-shaped protruded ground(TP) and three slots. The antenna element consists of a feed strip and two radiation strips (RS1, RS2), which only occupies a planar size of 15×25 mm² and generates dual-mode resonances at λ/8 and λ/4. The three slots and T-shaped protruded ground are utilized to reduce mutual coupling. Different slots can adjust different frequency bands independently. The working mechanism of the three slots is analyzed based on S-parameters and surface current distributions. The measured S₁₁ and S₁₂ are lower than −6 dB and -15 dB in the working bands, respectively. The radiation patterns and diversity performance are presented.

In this paper, a simple-fed, low profile, 9×10 elements quasi-lumped planar antenna array is presented. The proposed resonator employs a quasi-lumped element resonator that uses interdigital capacitor (IDC) in parallel with a straight strip inductor shorted across the capacitor. The array elements were designed and then excited by a feed network of four coaxial probes situated at the bottom plane but separated from the ground plane using a plastic material. The entire array is divided into four sub-array lattices of 5×5 elements and excited by a coaxial probe located at the centre of the sub-arrays antenna structure, thus exciting the centre resonator who in turn excites the neighbouring elements via proximity coupling. The probes are connected based on Wilkinson power divider principle to provide in-phase excitation. An explicit method is introduced to quickly obtain the array factor (AF) characteristics for such proximity coupled rectangular planar array. Radiation pattern and the array factor are presented, and are further compared with those obtained by the simulation and experimental results. The proposed antenna comprises 9×10 elements array, each of which is 5.8×5.6 sq. mm in size, and the entire antenna structure is about 120×80 sq. mm.

The scattering of an obliquely incident H-polarized plane electromagnetic wave by a magnetized plasma column is studied. It is assumed that the column is located in free space and aligned with an external static magnetic field. The emphasis is placed on the case where the angular frequency of the incident wave coincides with one of the surface- or volume-plasmon resonance frequencies of the column. The spatial structures of the field and energy flow patterns in the near zone of the column are analyzed, and the location of the regions with a greatly enhanced magnitude of the timeaveraged Poynting vector is determined. It is shown that the sign reversal of the longitudinal energy-flow component that is parallel to the column axis can occur when passing across the boundary between the inner region of the column and the surrounding medium.

This paper deals with reciprocity relations derivation for a nonlinear, stationary, homogeneous and isotropic plasma-like medium in an external homogeneous magnetic eld. A special case of such a medium is the charge carriers collective in semiconductors. It is shown that the classical reciprocity relations will be valid even in the presence of nonlinearity, and they can be used for Hall magnetometer bias compensation.

A graded material structure is optimized for broadband radome application by using hybrid method in this paper. In the optimization, dynamic range ratio (DRR) of real permittivity and loss of material are taken into considerations. By using an analytical function, the optimization problem with the DRR constraint is converted to an unconstrained problem. The proposed hybrid method is a combination of trust region method (TRM) and genetic algorithm (GA). Firstly (TRM) is applied to optimize the dielectric constant distribution. Then the result of TRM is used as initial value of GA. GA is employed to improve the global property of the results provided by TRM. Because TRM has the advantage of fast searching speed and GA has the advantage of global property, the hybrid method has the feature of fast convergence speed. And the jitter property of GA permittivity distribution is moderated. The effectiveness of the hybrid is validated through the designs of two broadband radome walls. The minimum power transmission efficiency is 81.9% ranging from 1 GHz to 18 GHz for normal incidence.