We present a topology of MIMO arrays of inductive antennas exhibiting inherent high crosstalk cancellation capabilities. A single layer PCB is etched into a 3-channels array of emitting/receiving antennas. Once coupled with another similar 3-channels emitter/receiver, we measured an Adjacent Channel Rejection Ratio (ACRR) as high as 70 dB from 150 Hz to 150 kHz. Another primitive device made out of copper wires wound around PVC tubes to form a 2-channels ``non-contact slip-ring'' exhibited 22 dB to 47 dB of ACRR up to 15 MHz. In this paper we introduce the underlying theoretical model behind the crosstalk suppression capabilities of those so-called ``Pie-Chart antennas'': an extension of the mutual inductance compensation method to higher number of channels using symmetries. We detail the simple iterative building process of those antennas, illustrate it with numerical analysis and evaluate there effectiveness via real experiments on the 3-channels PCB array and the 2-channels rotary array up to the limit of our test setup. The Pie-Chart design is primarily intended as an alternative solution to costly electronic filters or cumbersome EM shields in wireless AND wired applications, but not exclusively.
Two novel wire transmitarrays, which are designed using a pair of co-joined L-shaped probes, have been developed for X-band mobile communications. By adjusting the orientation of the L probes, the polarization of the transmitting wave can be easily made either vertical or horizontal. Floquet method has been used for characterizing the transmission responses, and both transmitarray unit cells are found to have achieved a phase range of greater than 380° and a linear phase sensitivity of 44.5°/mm. Wide -1 dB gain bandwidth larger than 10% is achievable in both the vertically and horizontally polarized full-fledged transmitarrays, with radiation efficiency of ~90%. The proposed transmitarrays have low radar cross section, which can be used for military applications.
This work proposes a radio-frequency interference (RFI) noise suppression filter with low noise generation for a power trace. This is based on a quarter-wavelength open-stub resonator (QWOSR) in a multilayered high-speed digital PCB (printed circuit board). RFI noise with frequencies at 2.4 GHz and 5 GHz is considered. The proposed filter structure is a four-layer PCB. The low noise generation includes the following schemes. The trace of the QWOSR is a stripline on the third layer. Four ground vias are added adjacent to the QWOSR via, which is short. Electromagnetic (EM) radiation noise, plan cavity resonance, ground bounce noise (GBN), and peak noise on insertion loss (|S_{21}|) are all reduced. The electric field distributions are elucidated to understand the effect of cavity resonance on the insertion loss (|S_{21}|) values of the proposed filter structure. The proposed filter structure significantly reduces the time-domain ground bounce and power noise whose frequency is equal or close to the center frequency of filter. Finally, favorable comparisons between simulated and measured results confirm the excellent low noise generation performance of the proposed filter structure.
This paper presents a numerical study of microwave scattering and emission from a foam-covered ocean surface. The foam layer is modeled as an inhomogeneous layer with randomly rough air-foam and foam-seawater boundaries. Kelvin's Tetrakaidecahedron structure is selected as the skeleton for simulating the air bubbles in the foam layer. The electromagnetic characteristics of the foam layer, including absorption and scattering coefficients for both vertical and horizontal polarizations, are calculated using a multilevel volume UV fast algorithm to accelerate the numerical computation of three dimensional Maxwell's equations. The surface scattering at air-foam and foam-seawater interfaces is determined using the integral equation model (IEM). The microwave emission from the foam-covered ocean surface, which accounts for multiple incoherent interactions within the foam layer and between the foam and interfaces, is modeled using the vector radiative transfer approach and numerically solved using the matrix doubling method. The model analyses of volume scattering and absorption of the foam layer reveal that the volume scattering coefficient of a foam layer increases with increasing water fraction at all selected frequencies, and its polarization dependence is negligible at a water fraction less than 2%. At 10.8 GHz and 18 GHz, the H-polarized scattering coe±cient is smaller than the V-polarized scattering coefficient for a larger water fraction; the opposite occurs at 36.5 GHz, at which V polarized scattering is weaker compared to H-polarized scattering. The model analyses of emission from a foam-covered ocean surface reveal that the emissivities at all selected operating frequencies have similar dependencies with water fraction and frequency, and they exhibit different sensitivities to water fractions. Moreover, the emissivities at high operating frequencies exhibit higher sensitivities to water fractions than the lower ones.
Results are presented for the transverse deflection of an electron beam by a long, straight wire carrying direct current. The experimental deflections are compared with three calculation methods based on the Lorentz force law (field theory) and both the Weber (direct action) and Ritz (emission) force formulae. The Lorentz force calculation is the conventional approach expressed in terms of electric and magnetic field components. By contrast the force formulae of Weber and Ritz do not contain any field vectors relating to E or B. The Weber force is based on direct action whereas the Ritz force expression is based on an emission/ballistic principle and is formulated in terms of a dimensionless constant, λ. The experimental beam deflections are for low speed (non-relativistic) electrons. Good agreement between experiment and theory is demonstrated for each approach. In fact, for the case of an infinitely long wire, all three calculation methods give identical results. Finally, the three approaches are contrasted when applied to the case of high speed electrons.
Microwave engineering of high average-power (hundreds of kilowatts) devices often involves a transition from a waveguide to a device, typically a resonant cavity. This is a basic operation, which finds use in various application areas of significance to science and industry. At relatively low frequencies, L-band and below, it is convenient, sometimes essential, to couple the power between the waveguide and the cavity through a coaxial antenna, forming a power coupler. Power flow to the cavity in the fundamental mode leads to a Fundamental Power Coupler (FPC). High-order mode power generated in the cavity by a particle beam leads to a high-order mode power damper. Coupling a cryogenic device, such as a superconducting cavity to a room temperature power source (or damp) leads to additional constraints and challenges. We propose a new approach to this problem, wherein the coax line element is operated in a TE_{11} mode rather than the conventional TEM mode. We will show that this method leads to a significant increase in the power handling capability of the coupler as well as a few other advantages. We describe the mode converter from the waveguide to the TE_{11} coax line, outline the characteristics and performance limits of the coupler and provide a detailed worked out example in the challenging area of coupling to a superconducting accelerator cavity.
This paper proposes the concept of sparse appended with the space tapering technique for the synthesis of an antenna radiation pattern. The procedure experiments on a Circular Antenna Array (CAA) configuration comprising of directional element (1+cos(φ)). The sparse initiates the minimum number of active elements in the CAA, while the space tapering technique gives the complex excitations that yield a beam pattern with constraints such as Side Lobe Level (SLL) and Beam Width (BW) in relation to Dolph-Chebyshev radiation pattern. The phase mode analysis, which is an built-in procedure in the proposed technique explores the circular antenna array configuration characteristics. The simulation results justify the effectiveness of the proposed technique for obtaining the desired radiation pattern synthesis.
Simulations of electromagnetic transients in transmission lines can be carried out using simple circuit model. In the case of applications of simple circuit models based on π circuits, there are problems mainly caused by numeric oscillations. The lumped-parameter π equivalent model can be used with some advantages. The numeric integration method applied to the simulations of electromagnetic transients is the trapezoidal rule. If this numeric method is associated to the π equivalent model, results obtained from the simulations are distorted by Gibbs' oscillations or numeric ones. The introduction of damping resistance parallel to the series RL branch of the π equivalent model can mitigate Gibbs' oscillations in obtained results. Voltage peaks caused by these oscillations can also be decreased. So, in this paper, the combined influences of the introduction of damping resistance, the number of π circuits and the time step are investigated searching for minimizing Gibbs' oscillations and the voltage peaks in electromagnetic transient simulations. For this, transient simulations are exhaustively carried out for determining the highest voltage peaks, ranges of damping resistances and other parameters of the model, which minimize these voltage peaks caused by Gibbs' oscillations.
One of the faults in medium voltage (MV) overhead power line is a high impedance fault (HIF) owing to low-current discharge to a tree (THIF). This type of fault generates signals in wide frequency bandwidth which may lead to electromagnetic interference (EMI) with neighboring devices and consequently results in degradation in the performance of nearby systems. This problem becomes more critical when MV power lines path is located in a wooded area in which there will be frequent transient conflicts between trees and power lines especially in the windy conditions. Given the importance of this issue, the ability of THIF to generate EMI is first demonstrated in this paper. Thereafter, a hybrid technique based on combination of quantile regression (QR) and empirical mode decomposition (EMD) is proposed to perform a feature extraction from THIF signals. By comparing the QR results of different samples of THIF signal with other similar signals, the validation of proposed method is depicted. In summary, the original contributions of current research include 1) assessing EMI due to THIFs, 2) using EMD in pre-processing of THIFs signals and extracting their main components, 3) recommending QR for the feature definition of THIF.
This paper presents a tutorial on photonic techniques for arbitrary RF waveform generation, highlights some key results and reviews the recent developments in this area. It also predicts that photonic integration of the entire system as compact photonic chip will be the major research focus and holds the key role for future developments.