Presently, wireless capsule endoscopy (WCE) is the sole technology for inspecting the human gastrointestinal (GI) tract for diseases painlessly and in a non-invasive way. For the further development of WCE, the main concern is the development of a high-speed telemetry system that is capable of transmitting high-resolution images at a higher frame rate, which is also a concern in the use of conventional endoscopy. A vital task for such a high-speed telemetry system is to be able to determine the path loss and how it varies in a radio channel in order to calculate the proper link budget. The hostile nature of the human body's channel and the complex anatomical structure of the GI tract cause remarkable variations in path loss at different frequencies of the system as well as at capsule locations that have high impacts on the calculation of the link budget. This paper presents the path loss and its variation in terms of system frequency and location of the capsule. Along with the guideline about the optimum system frequency for WCE, we present the difference between the maximum and minimum path loss at different anatomical regions, which is the most important information in the link-margin setup for highly efficient telemetry systems in next-generation capsules. In order to investigate the path loss in the body's channel, a heterogeneous human body model was used, which is more comparable to the human body than a homogenous model. The finite integration technique (FIT) in Computer Simulation Technology's (CST's) Microwave Studio was used in the simulation. The path loss was analyzed in the frequency range of 100 MHz to 2450 MHz. The path loss was found to be saliently lower at frequencies below 900 MHz. The smallest loss was found around the frequency of 450 MHz, where the variation of path loss throughout the GI tract was 29 dB, with a minimum of -9 dB and a maximum of -38 dB. However, at 900 MHz, this variation was observed to be 38 dB, with a minimum of -10 dB and a maximum of -48 dB. For most positions of the capsule, the path loss increased rapidly after 900 MHz, reaching its peak at frequencies in the range of 1800 MHz to 2100 MHz. During examination of the lower esophageal region, the maximum peak observed was -84 dB at a frequency of 1760 MHz. The path loss was comparatively higher during examination of anatomically-complex regions, such as the upper intestine and the lower esophagus as compared to the less complex stomach and upper esophagus areas.

In the received signal strength (RSS) based indoor wireless localization system, RSS measurements are very susceptible to the complex structures and dynamic nature of indoor environments, which will result in the system failure to achieve a high location accuracy. In this paper, we investigate the indoor positioning problem in the existence of RSS variations without prior knowledge about the localization area and without time-consuming off-line surveys. An adaptive sparsity-based localization algorithm is proposed to mitigate the effects of RSS variations. The novel feature of this method is to adjust both the overcomplete basis (a.k.a. dictionary) and the sparse solution using a dictionary learning (DL) technology based on the quadratic programming approach so that the location solution can better match the actual RSS scenario. Moreover, we extend this algorithm to deal with the problem of positioning targets from multiple categories, a novel problem that few works have ever concerned before. Simulation results demonstrate the superiority of the proposed algorithm over some state-of-art environmental-adaptive indoor localization methods.

In this paper, a novel end-loaded quarter-wavelength resonator is investigated for the designs of wideband tunable bandpass filter (BPF) and bandstop filter (BSF). The novelty of the resonator lies in that two varactors are added to the two ends of the resonator, and then its resonant frequency can be bi-directionally tuned. As a result, the theoretical frequency tuning range can be significantly extended to approximately double that of the conventional tunable quarter-wavelength resonator. For demonstration, the proposed resonator is applied to design wideband tunable BPF and BSF. As expected, the tuning ranges are 52.4% and 53.5% for the BSF and BPF, respectively. Good agreement can be observed between the simulated and measured results.

The non-equilibrium electron energy distribution function (EEDF) obtained via solving the Boltzmann equation is introduced into the fluid model, and the effects of the microwave frequency on the EEDF and air breakdown are investigated. Numerical simulations show that the breakdown threshold of the fluid model with the non-equilibrium EEDF agrees well with that of the reported experiments. The microwave frequency plays an important role on the shape of the non-equilibrium EEDF at low pressures. The breakdown time at the low pressures predicted by the Maxwellian EEDF is shorter than that from the non-equilibrium EEDF in low-frequency oscillating fields, while matches the latter in high-frequency oscillating fields.

Although many directive antennas operating in a narrow band of millimeter (mm) waves were reported, e.g., antennas for 60-GHz wireless local area network (WLAN), their wideband counterparts are still unpopular. Cavity-backed antennas (CBAs) are widely developed and reported in microwave frequency bands, but few literatures can be found about mm-wave CBAs in spite that their many properties are quite suitable for mm-wave applications. This paper presents a wideband unidirectional CBA with a bowtie exciter, operating in a frequency band of 40 ~ over 75 GHz, and it is carefully analyzed in terms of influences of all antenna components on radiation patterns, broadside gains, and reflection coefficients. Then, the antenna prototype is built by generic printed circuit board (PCB) technologies, and measurements prove the validity of simulations.

Effect of cold electron beam for Whistler mode waves have been studied for relativistic and non- relativistic subtracted bi-Maxwellian distribution and in the presence of perpendicular AC electric field to magnetic field by using the method of characteristic solutions and kinetic approach. The detailed derivation and calculations has been done for dispersion relation and growth rate for magnetosphere of Uranus. Parametric analysis has been done by changing plasma parameters: thermal velocity, ac frequency, temperature anisotropy etc. The effect of AC frequency on the Doppler shifting frequency and comparative study of relativistic and non- relativistic effect on growth rate are analyzed. The new results using subtracted bi-Maxwellian distribution function are found and discussed in relation to bi-Maxwellian distribution function. It is seen that the effective parameters for the generation of Whistler mode wave are not only the temperature anisotropy but also the relativistic factor, AC field frequency, amplitude of subtracted distribution and width of the loss-cone distribution function which has been discussed in result and discussion section.

Low-frequency ultra-wideband synthetic aperture radar is a promising technology for landmine detection. According to the scattering characteristics of body-of-revolution (BOR) along with azimuth angles, a discriminator based on Bayesian decision rule is proposed, which uses sequential features, i.e. double-hump distance. First, the algorithm estimates the target scatterings in all azimuth angles based on regions of interest. Second, sequential aspect features are extracted by sparse time-frequency representation. Third, the distributions of features are obtained by training samples, and then the posterior probability of landmine class is computed as an input to the classifier adopting Mahalanobis distance. The experimental results indicate that the proposed algorithm is effective in BOR target discrimination.

In order to gain consistent focusing quality all over the imaging region for wide-beam wide-swath airborne synthetic aperture radar (SAR), higher motion compensation (MoCo) accuracy at the edge of the swath is needed. In this letter, an improved MoCo approach is proposed, and its performance is validated by using simulated data, as well as real data collected by a P-band SAR system.

A method to design planar multilayer meander-line polarizers is given. The proposed procedure is based on transmission line circuit theory and on full-wave unit cell analysis in frequency domain. The hybrid combination of those two techniques paves the way for the polarizer design process and avoids heavy full-wave optimizations. This procedure is originally aimed for polarizers acting on lens antennas and is suitable for plane waves impinging with arbitrary angles on the polarizer. To validate the proposed method, two polarizers have been manufactured in Ka-band, one for normal and one for oblique incidence. Designs, prototypes and measurements made on a complete Ka-band lens antenna subsystem are shown in this paper.

The multifractal characteristics of return signals from aircraft targets in conventional radars offer a fine description of dynamic characteristics which induce the targets' echo structure; therefore they can provide a new way for aircraft target classification and recognition with low-resolution surveillance radars. On basis of introducing the mathematical model of return signals from aircraft targets in conventional radars, the paper analyzes the multifractal characteristics of the return signals as well as the extraction method of their multifractal features by means of the multifractal analysis of measures, and puts forward a multifractal-feature-based classification method for three types of aircraft targets (including jet aircrafts, propeller aircrafts and helicopters) from the viewpoint of pattern classification. The analysis shows that the conventional radar return signals from the three types of aircraft targets have significantly different multifractal characteristics, and the defined characteristic parameters can be used as effective features for aircraft target classification and recognition. The results of classification experiments validate the proposed method.

An effective development of a dual composite right/left-handed (D-CRLH) leaky-wave (LW) structure for dual-polarized antenna application is presented. The dual-polarized antenna consists of a two-section 3 -dB rat-race hybrid and two symmetrical substrate integrated waveguide lines. Each of the waveguide lines is periodically loaded with 15 transverse slots and 15 longitudinal slots. The dual-polarization capability and D-CRLH LW property of the antenna are analyzed and discussed. The S-parameters and gain patterns are presented for the antenna. Measured results are consistent with the simulated ones. The proposed LW antenna shows some desirable merits, such as the simplicity in design, low-cost fabrication, multi-band operation, flexible radiation directions and dual-polarization capability.

A wideband dual segment three element triangular dielectric resonator antenna (TDRA) has been proposed for applications in X-band. Proposed antenna has been fabricated and tested. The simulation study of the antenna is carried out using Ansoft HFSS simulation software. The simulation results for input characteristics and radiation patterns of the proposed antenna are compared with corresponding experimental results at the resonant frequency. The simulation results are in agreement with measurements. The return loss-frequency characteristics of the proposed antenna are also compared with those of single element, and three element TDRAs.

This paper presents a novel wideband to narrow band reconfigurable log periodic aperture coupled patch array. The wide to narrow band reconfiguration is realized by closing a selected group of slot apertures, to deactivate the corresponding group of patches. The patches are fed with a modulated meander line through aperture slots. A wideband mode from 7 - 10 GHz and three selected narrow band modes at 7.1, 8.2 and 9.4 GHz are demonstrated. Potentially, the number of sub bands can be increased or decreased as can the bandwidth of the sub bands by selecting a specific number of active elements. To verify and demonstrate the proposed design method, a prototype has been developed with ideal switches. Very good agreements between the measured and simulated results are presented.

In this paper, the measurement of the Doppler spectrum in a reverberation chamber (RC) is investigated. The estimation performance of the Doppler spectrum in the previous work is reformulated and analyzed. It is found that the previous RC Doppler spectrum evaluation is an inconsistent estimation. An improved method for evaluating the Doppler spectrum is presented, which makes use of the frequency stirring technique to enhance the estimation performance. In addition, the RC loading effect on the Doppler spectrum is investigated in this paper as well. Measurements are performed in a RC, based on which the Doppler spectrum is evaluated. It is shown that the improved method results in a smaller estimation variance and that the Doppler spread decreases with increasing RC loading.

Design and 3-D numerical simulation of a 140 GHz spatialharmonic magnetron (SHM) are presented. The effect of geometrical parameters of the side resonators of the anode block on the output power are considered using the results of a theory based on a single harmonic approximation approach. This theory enables the determination of the optimum geometrical parameters of the side resonators. SHM design evaluation is carried out via numerical simulations performed with a 3-D particle-in-cell (PIC) code embedded in CST-Particle Studio. Simulations of the SHM are performed without artificial RF priming and without assuming restrictive assumptions on the mode of operation or on the number of harmonics to be considered. Thus in our simulations the electromagnetic oscillations grow naturally from noise. The results of time evolved electron flow simulations and gradual formation of a single frequency RF oscillation are presented. The presented SHM shows stable operation in the π /2-1-mode at 140 GHz over a range of DC anode voltages extending from 11.3 kV to 11.5 kV and for an axial magnetic flux density equal to 0.79 T. RF Output power of the SHM varies from 2 kW to 11 kW over these voltages with a maximum efficiency of around 6.8%.

In this paper, a one-dimensional nonlinear fractal sea surface model has been established based on the narrow-band Lagrange model, which takes into account the vertical and horizontal skewnesses for the sea surface. By using the method of second-order small-slope approximation (SSA-II), the normalized radar cross section (NRCS) and Doppler spectrum of linear and nonlinear fractal sea surface are calculated. The calculated NRCS of the nonlinear fractal sea surface is larger than the linear surface for backscattering, especially for large incidence angles, which indicates the nonlinear surface has stronger scattering echoes. And the result of nonlinear fractal sea surface is also larger than the linear fractal sea surface for bistatic case, which is characterized as the discrepancies being small near specular direction, while the discrepancies becoming larger as the scattering angles departing from the specular direction. For the Doppler spectrum of sea surface, the nonlinearity of sea surface effects greatly enhances the Doppler shift and the Doppler spectrum bandwidth at large incidence angles, which are attributed the fact that the nonlinear-wave components propagate faster than the linear-wave components and the nonlinear fractal sea surface corrects the phase velocities by adding the horizontal and vertical skewness. And also, all the results can indicate the validity of this nonlinear model.

It is generally believed genetic algorithm (GA) is superior to particle swarm optimization (PSO) while dealing with the discrete optimization problems. In this paper, a suitable mapping method is adopted and the modified PSO can effectively deal with the discrete optimization problems of line array pattern synthesis. This strategy has been applied in thinned linear array pattern synthesis with minimum sidelobe level, 4-bit digital phase shifter linear array pattern synthesis and unequally spaced thinned array pattern synthesis with minimum sidelobe level. The obtained results are all superior to those in existing literatures with GA, iterative FFT and different versions of binary PSO, that show the effectiveness of this strategy and its potential application to other discrete electromagnetic optimization problems.

In this paper, a compact ultra-wideband microstrip-fed annular ring antenna with band notch characteristics for wireless local area network (WLAN) and dedicated short-range communication (DSRC) is proposed. The proposed antenna comprises an annular ring patch and a partial ground plane with a rectangular slot. The notched frequency band is achieved by etching a partial annular slot in the lower portion of the ring radiator. The centre frequency and bandwidth of the notched band can be controlled by adjusting the width and position of the annular slot. Measured results show that the proposed antenna achieved an impedance bandwidth of 3-10.6 GHz with a notched frequency band cantered at 5.5 GHz. Compared to the recently reported band-notched UWB antennas, the proposed antenna has a simple configuration to realize the band notch characteristics to mitigate the possible interference between UWB and existing WLAN & DSRC systems. Furthermore, a symmetric radiation patterns, satisfactory gain and good time domain behaviour, except at the notched frequency band, makes the proposed antenna a suitable candidate for practical UWB applications.

Traditional synthetic aperture radar (SAR) utilizes Shannon-Nyquist theorem for high bandwidth signal sampling, which induces the complicated system, and it is difficult to transmit and process a huge amount of data caused by high A/D rate. Compressive sensing (CS) indicates that the compressible signal using a few measurements can be reconstructed by solving a convex optimization problem. A novel SAR based on CS theory, named as parallel frequencies SAR (PFSAR), is proposed in this paper. PFSAR transmits a set of narrow bandwidth signals which compose the large total bandwidth. Therefore PFSAR only uses much less data to obtain the same resolution SAR image compared with a traditional SAR system. The data acquisition mode of PFSAR is developed and an algorithm of target scene reconstruction in pursuance of compressive sensing applied to PFSAR is proposed. The azimuth imaging of PFSAR is carried out based on Doppler Effect, and then, the range imaging is performed by using compressive sensing of parallel frequencies signal. Several simulations demonstrate the feasibility and superiority of PFSAR via compressive sensing.

The increasing popularity of a so-called transient motor current signature analysis requires the fault diagnostics parameters which could not be exposed to other factors irrelevant to the fault to make a precise assessment of the failure severity level. This challenging task needs a precise modeling of faulty motor behavior in various operating conditions at different fault severity levels. This paper introduces a new approach to a finite element analysis of an induction motor with broken rotor bars during startup. The approach is based on the principle of superposition and contributes to examination of the fault rotor backward rotating magnetic field and current components produced by such field separating them from stator currents. It gives a new sight on the behavior of a faulty motor during startup for the diagnosis purposes. Further analysis of the simulation data by means of the Extended Park's Vector Approach and the continuous wavelet transform and its experimental validation is also represented in the paper.