This article describes numerical solutions for the electromagnetic interactions, known as `wakefields', of a proton beam with an RF cavity and a beampipe. Using FDTD calculations, time-varying electromagnetic solutions are obtained. Unlike modal expansion methods, FDTD allows to compute transient wakefields due to proton beam passing through the structures. A popular time-frequency analysis approach, the short-time Fourier transform (STFT), is applied to the electromagnetic fields inside a resonant cavity and past an open-ended beampipe. STFT enables a more explicit interpretation of the transitions between the fields radiated by moving charges and the resonant modes. The described time-frequency analysis is useful to engineers and accelerator physicists who analyze proton beam dynamics. As an extension of electromagnetic simulations using an extended proton bunch, a numerical Green's function approach is proposed in order to account for the wakefields due to individual superparticles.
Satellite communication links operating at higher frequency bands suffer from signal outages due to rain attenuation. Site diversity technique is one of the rain fade mitigation techniques that can be employed over earth-satellite links to improve on system availability. In this study, we use 5-year rainfall rate statistics and the queuing theory approach to investigate the attributes and behavior ofintense rain storms along an earth-space link over Durban, South Africa (29˚52'S, 30˚58'E), a sub-tropical climate. Thereafter, a comparison is made with results obtained in a related study in Jimma, Ethiopia (7.6667˚N, 36.8333˚E), which is a tropical climatic region. Verification of the best fit distribution is done through the application of the root mean square error (RMSE) and CHI squared statistics. Results of these analysis tools confirm the suitability of the proposed distributions with RMSE error margin in the range 0.0024 to 0.0128, and a χ2 statistics value of 0.4070. The spike service time for such rain storms is found to follow Erlang-k distribution in both regions of South Africa and Ethiopia as opposed to earlier determined exponential distribution. In addition, the analysis shows that there exists a power law relationship between the rain spike maximum rain rate and its diameter. This relationship is further utilized in the development of the rain cell sizing model that can be used for site diversity fade mitigation. Furthermore, the Markov chain techniqueis employed to determine the occurrence behavior of shower and storm rainfall regimes, and their contributions to rain attenuation over a slant path radio link.
A compact planar double inverted-F antenna (IFA) is proposed in this work. The antenna, composed of a shared short arm and two L-shaped open arms, has three operating bands, 1.7-1.9 GHz, 2.25-2.48 GHz and 5.33-5.8 GHz for Wi-Fi and LTE applications. It has the length of 80 mm, width of 23 mm and height of 1.6 mm. Near omnidirectional coverage of radiation patterns in x-y and x-z plane, are realized with peak gain of 3.3 dBi, 2.1 dBi and 4.1 dBi at 1.8 GHz, 2.4 GHz and 5.5 GHz, respectively. Based on reflection coefficients with different dimensions and current distributions, the functions of arms and via holes are analyzed in detail, which provide a useful guidance for design of multiband PIFA antennas.
Because traditional eigen-subspace projection (ESP) methods cannot cancel the main lobe interference, an improved ESP algorithm and an orthogonal array of antenna are proposed to overcome this problem. Based on the orthogonal antenna array, the proposed algorithm combines ESP with ICA and signal blocking methods, which implements the extraction of part of the main lobe interference and optimized the estimation of the interference subspace. Both simulation and experiment results show that the improved ESP algorithm provides robust cancellation capability of main lobe and sidelobe interference for super low frequency (SLF) communication.
In this paper, a high power, air suspended stripline (SSL) T junction power divider at L band microwave frequencies is introduced. The power divider operating frequency is centered at 1.3 GHz. In this new configuration, the only dielectric used is air to have maximum power handling capability. An excitation transition from coaxial cable to the SSL transmission line is explained. The SSL was fabricated using alumi-num sheets to gain the advantage of low cost. The power divider design was validated using circuit and 3D full wave simulations and confirmed using experimental measurements with all agreements. It has been proved that the power divider attenuation has sharp rejection characteristic at the designed frequency (-20 dB at 1.3 GHz). The power divider can be used as a feeder for devices used in high power applications.
In this paper we present a novel approach for calculating the torque between two filamentary circular coils with inclined axes whose centers are at the same plane. In this approach we use Grover's formula for the mutual inductance between two filamentary circular coils with inclined axes whose centers are at the same plane. The filament method is applied to the combination comprising a filamentary circular coil and a thin wall solenoid. As the comparative method we give the new formula for this coil's combination which is derived from Chester Snow's formula for two solenoids with inclined axes.
Mining and mineral exploration are very important in the global economy. In mining operations, communication systems play vital roles in ensuring personal safety, enhancing operational efficiency and process optimization. Multiple Input Multiple Output (MIMO) systems have been widely used in the mine environment to suppress the multi-path problem of the tunnel and enhance the capacity of the channel. In order to realize the optimal performance of MIMO system, spatial characteristics of wireless signal in an underground tunnel must be considered. In this paper, the wave propagation model combined with the modal theory and ray theory is used to simulate mine underground wireless channel. Meanwhile, the theoretical models of the signal Angular Power Spectrum (APS) and Angular Spread (AS) are constructed. After simulation and comparison, the following conclusions can be drawn: the APS distribution of the wireless signal is similar to the Gaussian distribution; the position of the antenna in the cross section of the mine tunnel has a small influence on the signal AS, which can be neglected; the roughness of the mine tunnel wall can change the characteristic of the signal AS to some extent.
Because of the maneuvering of hypersonic target, the tracking of near space hypersonic target is difficult. In this paper, a new adaptive tracking algorithm based on aerodynamic model and improved square root cubature kalman filter is proposed. The adaptive piecewise constant Jerk model, gives the acceleration recursive process based on the dynamic model. Considering the non-linear characteristic of the target state model and the observation model, the improved square-root cubature kalman filter is applied to estimate target state. The simulation results under different maneuvers conditions indicate that the proposed method has higher accuracy than original aerodynamic model. The research provides a feasible solution to the further improvement of the real time tracking accuracy of near space hypersonic target.
In this paper, a compact triple-band bandpass filter using metamaterial (MTM) inspired structure with controllable transmission zero (TZ) position has been proposed. The gap between feed lines develops electrical coupling and provides series capacitance. An open loop rectangular ring resonator with meander line and rectangular stub develops electric and magnetic couplings separately. Defected ground structure (DGS) provides proper impedance matching and increases the passband. In order to validate metamaterial (MTM) behaviour of designed filter dispersion diagram has been plotted. The position of transmission zero can be controlled by electric and magnetic coupling. The measured operating frequency ranges of three passbands are 1.85-2.15 GHz, 3.55-3.73 GHz and 3.85-4.0 GHz with the 3 dB fractional bandwidth of 15.63, 4.94 and 3.82 percent, respectively. It has minimum insertion loss of 0.7 dB, 0.5 dB and 0.5 dB at the 1st, 2nd, and 3rd passbands, respectively. The electrical size of the proposed filter is 0.16λg×0.15λg, where λg is the guided wavelength at zeroth order resonance (ZOR) frequency of 1.92 GHz.
To provide better care to the people, who are living in rural areas and whoever in need of emergency medical care, it becomes essential to develop remote monitoring health care applications. Body Area Networks (BAN) that are formed with wearable or implanted wireless sensor devices will play an important role to achieve the above task. Since the communication in BAN is of short communication distance and higher data rate, the Ultra-Wideband (UWB) radio signals make themselves as the right candidates due to their inherent characteristics. This requires more research in design and development of UWB transceivers, especially for implantable biomedical devices. This paper proposes a UWB antenna design and a numerical channel model to predetermine the path loss characteristics of an on-body to in-body channel in UWB. The proposed model has been developed using ray tracing procedures and includes the antenna polarization and radiation pattern. In addition, the predicted results have been validated by measurements conducted with honey based liquid phantoms.
In this paper we present a new compact microstrip lowpass filter using a П-H-П-DGS resonator etched in the ground plane and two patches compensated capacitors placed on the top layer. Two DGS shapes are electromagnetically coupled. The proposed lowpass filter has shown improvement by adding a square microstrip to the single DGS resonator. The design procedure is validated using the commercial full-wave EM MoM simulator Microwave Office. Simulated as well as measured results exhibit sharp roll-off (ξ) of 34 dB/GHz and create a transmission zero at around 4 GHz with attenuation level -34 dB near the passband. On the other hand, the proposed LPF has shown wide stopband bandwidth with rejection better than -20 dB from 3.5 GHz up to 11.5 GHz, while the size of the whole structure is smaller (20 mm x 20 mm). Finally, the proposed filter structure was fabricated and measured. The measurements are in a good agreement with the simulated results.
Slot skew is applied as a method to increase the armature winding voltage waveform quality of synchronous hydro generators. Skew that matches the region of one slot pitch can effectively damp stator slot harmonics. However, achieving this condition can be difficult I some manufacturing cases, especially for the machines with greater axial length. That is why other methods are commonly used to increase the voltage waveform quality of large hydro generators. One such method is based on the damper winding slot pitch choice which ensures reduction of stator slot harmonics from the main magnetic field. Appropriate placement of damper bars over the pole shoe does not represent a significant technological problem and is much simpler to manufacture in compare with the slot skew or the fractional armature winding methods. The downside of damper slot pitch adjustment method is the damper bar currents incensement in steady state condition of the generator, which increases damper winding losses and also the rotor temperature. In order to decrease damper winding current for long term operating and enable the generator pole shoe design with smaller cross section damper bars, a combination of damper slot pitch and partial slot skew can be utilized. This paper gives insight on consequences that can occur for voltage waveform if slot skew does not not fully match the stator slot pitch and the advantages of above mentioned combined method for the design optimization of salient pole synchronous generator.
A theoretical investigation of the interaction of electromagnetic plane waves with a uniaxial crystal slab, bounded by two graphene layers from both sides, placed in free space is presented in this paper. An 8×8 matrix method is developed using boundary conditions at a graphene-uniaxial anisotropic crystal interface and a uniaxial anisotropic crystal-graphene interface. The developed matrix is used to find reflection and transmission coefficients by Crammer's rule. Numerical results are presented to demonstrate the effect of frequency of the incident wave, thickness of the uniaxial crystal slab, and Fermi energy of the graphene on the reflected and transmitted energies. The presented formulations and results are confirmed by published results of some limited cases.
This paper presents a calibration technique for phased array radars. The real embedded patterns of the array elements are measured independently in operating mode, while taking antenna coupling and other parasitic effects into account. The proposed technique does not affect the operation of the antenna array. The use of suitable switches integrated in the beamforming network of the array allows introducing sparsity into the measured summed signal. This enables the extraction of the angular dependent calibration coefficients by means of a dedicated compressed sensing approach.
The fast development of millimeter wave (mmWave) wireless communications and the associated concerns of potential negative impact on human health instigates the study on effects of mmWave frequency on the human body after exposure to electromagnetic field in terms of specific absorption rate (SAR) and temperature rise in computer simulation technology (CST). SAR distributions due to radiating source antenna were investigated using the finite difference time domain (FDTD) method in single and layered human tissues by examining the 1 g SAR (gram mass averaging) and point SAR (without mass averaging) at mmWave frequencies of 28, 40 and 60 GHz. The bioheat equation was used to find the temperature elevation in tissues. The FDTD grid size used in the computation was 1.00, 0.75, and 0.50 mm at 28, 40 and 60 GHz, respectively. The results concluded that at the radiated power of 20 and 24 dBm, SAR levels (without mass averaging) in the tissues at 28 GHz were less than 40 and 60 GHz. It was found that the temperature increase in the three layer model was 2-3 times higher than that in the single layer model. However, the temperature elevation never exceeded 1˚C in all the determined cases which was well below the threshold value for the generation of any adverse thermal effects in the tissues. Moreover, the effect of distance between the source and tissue model was investigated. It was found that the SAR decreased as the distance increased from the radiating source. The results presented here will assist researchers in examining and simulating the performance of upcoming mmWave wireless networks in terms of exposure to human tissues.
Using impulse response with a 3D algorithm is a novel free-space radiation pattern reconstruction technique with accuracy greater than 1 dB in all antenna under test (AUT) azimuth and elevation angle orientations inside a non-anechoic environment. A quantitative comparison between impulse response with a 3D algorithm and impulse response with 2D, a previous technique, is performed using quantifiers. Benefits of the proposed 3D free-space radiation pattern reconstruction algorithm are single-frequency characterization and reuse of the 3D impulse response of the environment.
This paper presents a hybrid design of Sierpinski Carpet and Minkowski antenna for wireless applications. The hybrid antenna is designed, simulated and fabricated on an FR4 substrate with thickness 1.6 mm and dielectric constant 4.4. The dimensions of antenna are 45 x 38.92 x 1.6 mm3 which operates at various frequencies 3.43 GHz, 4.78 GHz, 6.32 GHz, 8.34 GHz and 9.64 GHz, and can be used for WiMax, C-band applications, Point-to-point Hi speed wireless communication and X-band (satellite Communication) applications. The measured results are also compared with the simulated ones which are in agreement with each other. Ansoft High Frequency Structure Simulator (HFSS) is used to design and simulate the antenna.
A backscattering model of the average signal power function (SPF) for laser radar 3D range imagery obtained using detector arrays for a complex target with rough surfaces is presented. The model relates the average power at the receiver to the laser pulse, target shape, optical scattering properties of the surface materials, angle of incidence, and other factors. The optical scattering properties of the material are characterized using the bidirectional reflectivity distribution function (BRDF). The effects of the pulse width on the resolution of the 3D range imagery are analyzed. The proposed model can be used to demonstrate 3D laser radar systems and can also be used to generate a library of model data sets for automatic target recognition (ATR) applications.
The study of electromagnetic field coupling to an electrically large structure is essential, in order to assess the degree of protection to be provided to harden the electronic or electrical system of interest, against electromagnetic fields. The electromagnetic field coupling study can be done by computational and experimental techniques. In this paper, we have studied the high altitude electromagnetic pulse (HEMP)electromagnetic field coupling to a large antenna structure using electromagnetic dimensional scale modeling approach, in the frequency range of 1 kHz to 100 MHz. This frequency range has been chosen because most of the energy of the HEMP lies in this frequency band .
This paper presents a compact high-isolation dual-polarized dipole antenna with an artificial magnetic conductor (AMC) reflector. The proposed antenna is composed of a radiating element, two short pins and a 7×7 AMC array. By introducing two short pins, the port isolation is lower than -33 dB in the whole band on two ports. With the ring and AMC reflector, the dimension of the proposed antenna is only 0.36λ0×0.36λ0×0.16λ0 at 2.2 GHz. The antenna also achieves a 10-dB return loss bandwidth from 1.6 to 2.78 GHz (54%) for both ports. The gain of the proposed antenna is around 8 dBi, and the cross-polarization is about 30 dB. Due to these properties, the proposed antenna can be applied to 2G/3G/long term evolution (LTE) base station and WLAN/WiMAX applications.