The shimming method used for producing high field homogeneity of the open permanent main magnet for magnetic resonance imaging (MRI) is researched in this paper. The central shimming method based on integer programming is proposed, which fulfills the combination of optimal theory and the practical manual shimming. The formulation of shimming is solved by using Lingo software and the numerical analysis method is used to compute the contribution of small shim arrays. The homogeneity of imaging region is eventually advanced nearly by 50%.The validity of the method is validated by using simulation test of shimming. The efficiency of shimming is improved through experiment corporated with the manufacturing enterprise.

Perfect electromagnetic conductor (PEMC) is a medium where certain linear combinations of electromagnetic fields are required to vanish. Since PMC has found important applications in antenna design, one may expect that PEMC will also have potential for similar applications; therefore it is important to investigate its radiation properties. In this paper, dyadic Green functions in integral forms have been derived for a structure with a dielectric layer on a PEMC plane. Whereas electric and magnetic dyadic Green functions is required to satisfy the dyadic mixed boundary condition on PEMC surface, a new classification of the electric and magnetic dyadic Green functions has been introduced based on parameter M of PEMC boundary. This classification is general and contains classes of dyadic Green functions which satisfy Dirichlet and Neumann boundary conditions.

In classical antenna books, the field radiated by a filamentary antenna is calculated integrating the electrical current induced over the wires as if it was a primary (impressed) source. This is no technically incorrect, but is not rigorous. In this paper some formal steps are added to the classical procedure to do it more rigorous.

The ambiguity function of a kind of chaotic signal radar using Colpitts oscillator is investigated and compared in several aspects. The Colpitts oscillator with specific value of capacitance, inductance and resistance can generate chaotic signal with frequency band from direct current to several gigahertz. The chaotic signal is obtained from simulation and experiment. The auto-ambiguity functions of the chaotic signal show that the chaotic signal of such oscillator is ideal for radar application with both high range and range rate resolution. The cross-ambiguity function also indicates the chaotic signal has excellent capabilities in the electronic countercountermeasures (ECCM).We also present the resolution of range with the spectrum from experiment.

A broadband method is introduced to measure the effective constitutive parameters of artificial magnetic materials. The method is based on the microstrip line topology, thus making it easy to retrieve the constitutive parameters over a wide band of frequencies. To demonstrate the effectiveness of this method, artificial magnetic materials with Fractal Hilbert inclusions are fabricated and characterized. Good agreement between the experimental and numerical simulation results verifies the accuracy of the proposed method.

To efficiently solve large dense complex linear system arising from electric field integral equations (EFIE) formulation of electromagnetic scattering problems, the multilevel fast multipole method (MLFMM) is used to accelerate the matrix-vector product operations. The inner-outer flexible generalized minimum residual method (FGMRES) is combined with the symmetric successive overrelaxation (SSOR) preconditioner based on the near-part matrix of the EFIE in the inner iteration of FGMRES to speed up the convergence rate of iterative methods. Numerical experiments with a few electromagnetic scattering problems for open structures are given to demonstrate the efficiency of the proposed method.

The shadowing relationship between facet elements can be determined rapidly through analytical expressions. On the basis of modeling using curved surfaces, an effective shadowing processing algorithm is proposed which is in combination with that used in the shadowing judgement of facet elements. Firstly several sampling points are taken on the ergodic curved surface element to construct a group of facet elements, which can replace the curved surface element. Then the shadowing processing between the stationary phase point and the ergodic curved surface element is converted to that between the stationary phase point and several facet elements, thus avoiding utilizing optimization method and can increase the computation speed. Similarly, the shadowing processing between the stationary phase segment and the ergodic curved surface element is converted to that between the stationary phase segment and several facet elements. And the trimming algorithm is used to accurately find the visible part of the stationary phase segment, which gets rid of the rough shadowing processing technique that determines the visibility of the whole stationary phase segment through the visibility of the center of the stationary phase segment. Therefore, the computation precision is greatly improved. When there exists a huge number of curved surfaces, maximum-minimum preprocessing is utilized to increase the computation speed. Examples show that this novel algorithm is superior to the traditional one in both computation speed and precision.

According to the Coarse Wavelength Division Multiplexing (CWDM) wavelength dependent transmission characteristics, a wide range fiber Bragg grating (FBG) demodulation method is proposed and experimentally demonstrated in this paper. The relationship between system input and output is obtained through analysis, and verified experimentally. Particularly the influence of light source power on demodulation precision and calibration value is analyzed. The wavelength demodulation range of the system is about 10 nm, which can realize the measurement of 8000με; The precision can be 3~5 pm. Since the system is compact, low cost and passive, it is able to be integrated as a portable demodulation module.

An externally modulated NTSC 77-channel erbium-doped fiber amplifier (EDFA)-repeated system employing Fabry-Perot (FP) etalon at the receiving site to improve system performance was proposed and demonstrated. In comparison with conventional externally modulated fiber optical CATV transport systems, good performance of carrier-to-noise ratio (CNR), composite second order (CSO), and composite triple beat (CTB) were achieved for the full channel band over a 100-km single-mode fiber (SMF) transmission. Our proposed systems are suitable for the long-haul fiber optical CATV transport systems.

A bidirectional high gain four-element printed dipole array for WLAN (2.4/5.8 GHz) applications is analyzed and successfully implemented in this paper. Each element used is a double-side printed dipole fed with a balance twin-lead transmission line. A wide-band balun is implemented for the dipole array. Both simulated and measured data are pretty matched. According to the measured results, the bandwidth with return loss less than -10 dB is about 280 MHz (2250-2530 MHz) and 510 MHz (5470-5980 MHz) in the two operating bands, the measured gain for 2.4 GHz band is between 4.5 and 5.9 dB, and 6.1-8.9 dB for 5.8 GHz respectively. Good shaped patterns have also been attained by tuning parameters of the dipole array.

Based on composite right/left-handed (CRLH) transmission line (TL),a novel series feed network for microstrip arrays is proposed and its theoretical analysis and experimental results are presented. In the present structure,p ower dividers and open-ended stubs are employed to even the amplitude distributions among different output ports,while CRLH TLs and short meandering lines are used to compensate the phase delay caused by the different lengths of righthanded (RH) TLs. Finally,an X-band series feed network is designed and fabricated as an example. The simulated and measured results indicate that the present design can achieve even amplitude and phase distributions among different output ports in the range of 8.8-9.6 GHz. And it has other advantages such as a compact size of 350mm×50mm and good return loss which is higher than 22 dB in the operation frequency.

The solution to the problem of far field radiation from an arbitrarily oriented Hertzian dipole in an electrically gyrotropic medium is found with the application of dyadic Green's function (DGF) technique. The form of the DGF, which is expressed as the sum of two single dyads, simplifies the derivation of the far fields significantly in comparison to the existing methods. The far field integral is evaluated analytically using the method of steepest descent. The numerical results for the radiation fields are presented in different frequency bandwidth using Clemmow-Mually-Allis (CMA) diagram. It is shown that the operational frequency bandwidth and the orientation of the antenna, which give the highest directivity and gain, can be determined when the CMA diagram is employed. Our analytical results are compared with the existing ones which were obtained using different techniques. Agreement is observed on all of them. The results presented in this paper can be used for radiation problems involving space exploration, radio astronomy or laboratory plasmas.

In this letter, we use two embedded isolation moats which have different size to obtain the wide stopband elimination performance. The proposed structure is realized by embedding the double isolation moats between power and ground planes. The suppression frequency range of the proposed structures is from 1.2 to 7.2 GHz and the peak noise improvement in time domain is 36%. Furthermore, the proposed structure uses two elimination cells to avoid the parasitic effect generated in the frequency range of several hundred MHz.

Bootlace lens is the most appropriate choice for multiple beam forming. A compact symmetric bootlace lens has been developed. Here, a theoretical modal is developed which predicts the primary amplitude distribution across the array port of the lens. Amplitude distribution depends upon the gain performance of array contour of the lens. This theoretical modal develops a symmetric bootlace lens without complex analysis.

This paper presents a numerical and experimental analysis of a horizontally polarized HF antenna?The antenna is aimed to be compact, wideband and high power gain. A V-shape wire-structured pentagonal antenna has acceptable performance in both aspects of gain and VSWR. The V-shape structure yields a comparatively high gain relative to the 27 m radiation arms. By incorporating both ground-loaded guys and convex pentagon-shape arms, the antenna can cover the whole HF band. The measured and simulated results show that the VSWR of this antenna is within 2.55:1 over 3~30 MHz and the average power gain is about 11 dBi.

ℜMulti-carrier system has been fuelled by large demand on frequency allocation, resulting in a crowded spectrum as well as large number of users requiring simultaneous access. Existing wireless systems may be utilized single frequency, single antenna and pulse for carrier transmission and reception. Problems of such system is that in case of failure the total system will become non operational. So we established a distributed system in terms of multi-carrier, multi-antenna and coded pulse can provide a more suitable communication and sensor gives rise to DSSS-OFDM-MIMO based hybrid technology is the ultimate solution. This technology is a promising technique for high-data-rate broadband wireless communications and radar because it can reduce interference, multipath effect, jamming and higher target resolution as compared to conventional communication & radar etc. The proposed techniques improve the performance of OFDM, DSSS and MIMO based wireless communications and sensing for ITS and other applications. Finally this system can be implemented using Software defined Radio to get continuous connectivity of the system.

Space-Time Adaptive Processing (STAP) is a well known technique in the area of airborne radars, which is used to detect weak target returns embedded in strong ground Clutter, Jammers, and receiver Noise. STAP has the unique property of compensating for the platform motion induced Doppler spread, thus making detection of slow targets possible. But there are others problems resulting from the characteristics of the airborne radar that may limit the performance of detection of the radar, for instance, the ambiguities (Range or Doppler ambiguities) which are dependent on the value of the pulse repetition frequency (PRF). When PRF is high, range ambiguities appear; when PRF is small, Doppler ambiguities appear; and both are present when PRF is medium. To resolve Doppler ambiguities staggering of PRF is used. And to resolve problem of high computational cost of optimal space-time processing, reduced-rank methods are used. In this paper, STAP processing on the airborne radar is briefly reviewed for motivation, and the effect of a radar parameter dimensionality set on the STAP and the Reduced-Rank STAP is discussed.

This paper presents a reconfigurable of multiple element microstrip rectangular linear array antenna integrated with radio frequency (RF) switches. The corporate feed design concept is used to excite the linear array antenna that consists of 8 elements of rectangular patches at 5.8 GHz. Two PIN diode switches were deployed at the feeding line to activate the two arrays of patches that is located on the left and right side of the antenna structure. The behavior of the reconfigurable multiple element linear antenna array system has been investigated with respect to the beam shaping characteristic. The comparisons of the performance between two structures, with Wilkinson Power Divider (WPD) and without WPD are discussed in this paper. Two different beam patterns were achieved through the reconfigurable antenna at different number of elements design that incorporates with PIN diode switches and modified WPD concept. The simulations and the measurement results for 4 and 8 elements array antenna structure are presented.

In this paper, direction-of-arrival (DOA) estimation of a single narrow-band source with uniform linear arrays is addressed. The basic idea is to convert the received data to a correlation sequence which can be modelled as a noisy sinusoid. Then the computationally attractive and accurate generalized weighted linear predictor frequency estimator is applied for DOA determination. The effectiveness of the proposed method is demonstrated via computer simulations.

Bismuth-based EDF (Bi-EDF) is comprehensively studied as an alternative medium for optical amplification. The bismuth glass host provides the opportunity to be doped heavily with erbium ions to allow a compact optical amplifier design. The gain spectrum of the Bi-EDF amplifier has a measured amplification bandwidth of 80 nm with a quantum conversion efficiency of 20% obtained using 1480 nm pumping and 215 cm long of doped fiber. A multi-wavelength laser comb is also demonstrated using a four-wave mixing effect in a backward pumped Bi-EDF. The laser generates more than 10 lines of optical comb with a line spacing of approximately 0.41 nm at 1615.5 nm region using 146 mW of 1480 nm pump power.