This paper presents a simple method of tuning the AMC band of a high-impedance surface. The tunability is obtained with only two varactor diodes and a simple biasnetwork. The proposed structure, when used as a ground plane for a microstrip antenna, splits the resonance frequencies on the two sides of a reference antenna frequency. The resonance split is analyzed by employing cavity model and transmission line model of the patch antenna. Considerable tuning range is obtained in both the split bands. The simulated, measured and calculated results are found to be in good agreement.

The design and analysis of a high power and high efficiency helix traveling-wave tube operating in the Ka-band are presented. First, the double-slotted helix slow-wave structure is proposed and employed in the interaction circuit. Then, negative phase-velocity tapering technology is used to improve electronic efficiency. From our calculations, when the design voltage and beam current are set to be 18.45 kV and 0.2 A, respectively, this tube can produce average output power over 800 W ranging from 28 GHz to 31 GHz. The corresponding conversion efficiency varies from 21.83% to 24.16%, and the maximum output power is 892 W at 29 GHz.

Evolutionary Search Algorithms (EA) have been intensively used in solving numerical optimization problems. Since design of antenna arrays is a numerical optimization problem, EAs have been intensively used in solving antenna arrays design problems. Although EAs are widely used in antenna array design problems, a performance comparison study of the intensively used EAs for circular antenna array design problem has been scarcely studied. In this paper, 3 different circular antenna array design problems have been solved by using 15 different evolutionary search algorithms (i.e., ABC, ACS, BSA, CK, CLPSO, CMAES, DE, E2-DSA, EPSDE, GSA, JADE, JDE, PSO, SADE, S-DSA). The objective function designed for solution of the relevant circular antenna array design problems ensures minimization of side lobe levels, acquisition of maximum directivity, and null control of the non-uniform, planar circular antenna array. Obtained statistical analysis results show that S-DSA solves the relevant circular antenna array design problems statistically better than the other evolutionary algorithms used in this paper.

The uniform asymmetrical microstrip parallel coupled line is used to design the multi-section unequal Wilkinson power divider with high dividing ratio. The main objective of the paper is to increase the trace widths in order to facilitate the construction of the power divider with the conventional photolithography method. The separated microstrip lines in the conventional Wilkinson power divider are replaced with the uniform asymmetrical parallel coupled lines. An even-odd mode analysis is used to calculate characteristic impedances and then the per-unit-length capacitance and inductance parameter matrix are used to calculate the physical dimension of the power divider. To clarify the advantages of this method, two three-section Wilkinson power divider with an unequal power-division ratio of 1:2.5 are designed and fabricated and measured, one in the proposed configuration and the other in the conventional configuration. The simulation and the measurement results show that not only the specified design goals are achieved, but also all the microstrip traces can be easily implemented in the proposed power divider.

This paper proposes an amplify-and-forward (AF) distributed relay network consisting of a one-source-one-destination pair and two-level N relays. Optimal relay amplifying matrices (or vectors) at the relays in the first and second levels are determined based on the minimum mean square error (MMSE) criterion. Power is globally, locally, and aggregately constrained at the relays in the first and second levels, independently or separately. With the derived optimal relay amplifying matrices, bit error rate (BER), mean square error (MSE) behavior, and the achievable rate are investigated. It is also proven that minimizing the MSE is equal to maximizing the signal-to-noise ratio (SNR) in a three-hop AF wireless relay network.

An ultra-wideband (UWB) antenna with triple band-notched characteristics is presented in this paper. The triple-notched bands (5.15-5.35 GHz and 5.725-5.825 GHz for WLAN, 7.9-8.395 GHz for X-band) are achieved by using only one novel composite resonator with multiple resonant characteristics. The resonator is placed on the back surface of the substrate and connected to the radiation patch through one via-hole. An equivalent circuit model is built for analyzing the band-notched characteristics. Moreover, the notched bands can be adjusted independently, and the resonator structure is very compact.

This study presents NMR signal detection by means of a superconducting channel consisting of a Nb surface detection coil inductively coupled to a YBCO mixed sensor. The NMR system operates at a low field (8.9 mT) in a magnetically shielded room suitable for magnetoencephalographic (MEG) recordings. The main field is generated by a compact solenoid and the geometry of the pickup coil has been optimized to provide high spatial sensitivity in the NMR field of view. The Nb detection coil is coupled to the mixed sensor through a Nb input coil. The mixed sensor consists of a superconducting YBCO loop with 2-μm constriction above which two Giant Magneto Resistance sensors are placed in a half-bridge configuration to detect changes of the bridge voltage as a function of the flux through the YBCO loop. The sensitivity of the receiving channel is calibrated experimentally. The measured spatial sensitivity is in agreement with the simulations and is ~10 times better than that of the stand-alone mixed sensor. A NMR echo at 375 kHz shows a SNR only a factor 4 smaller than a tuned room temperature coil tightly wound around the sample, with a noise level which is a factor 3 better than for the volume coil. Our results suggest that mixed sensors are suitable for the integration of low-field MRI and MEG in a hybrid apparatus, where MEG and MRI would be recorded by SQUIDs and mixed sensors, respectively.

The goal of array processing is to gather information from propagating radio-wave signals, as their Direction Of Arrival (DOA). The estimation of the DOA can be carried out by extracting the information of interest from the steering vector relevant to the adopted antenna sensor array. Such task can be accomplished in a number of different ways. However, in source estimation problems, it is essential to make use of a processing algorithm which feature not only good accuracy under ideal working conditions, but also robustness against non-idealities such as noise, limitations in the amount of collectible data, correlation between the sources, and modeling errors. In this work particular attention is devoted to spectrum estimation approaches based on sparsity. Conventional algorithms based on Beamforming fail wherein the radio sources are not within Rayleigh resolution range which is a function of the number of sensors and the dimension of the array. DOA estimation techniques such as MUSIC (MUltiple Signal Classifications) allow having a larger spatial resolution compared to Beamforming-based procedures, but if the sources are very close and the Signal to Noise Ratio (SNR) level is low, the resolution turns to be low as well. A better resolution can be obtained by exploiting sparsity: if the number of sources is small, the power spectrum of the signal with respect to the location is sparse. In this way, sparsity can enhance the accuracy of the estimation. In this paper, an estimation procedure based on the sparsity of the radio signals and useful to improve the conventional MUSIC method is presented and analyzed. The sparsity level is set in order to focus the signal energy only along the actual direction of arrival. The obtained numerical results have shown an improvement of the spatial resolution as well as a reduced error in DOA estimation with respect to conventional techniques.

Gaussian beams techniques are high-frequency asymptotic methods that can be used to model the propagation/interaction of fields in a variety of problems. In this article, an expansion is proposed to express the scattering of magnetic/electric currents from a curved interface in terms of a new kind of elementary beams, the conformal Gaussian beams. The expansion characteristics rely on the physical properties of the configuration, which leads to represent the scattering with a small number of conformal Gaussian beams. An analytical formulation for the conformal Gaussian beams is developed, which expression is derived from an asymptotic evaluation of the radiation integrals valid at great distance from the interface. An example is presented to show that this analytical formulation is in good agreement with the reference result. Numerical tests are led on the expansion in order to show that the scattering can be represented with accuracy by adding the contribution of conformal Gaussian beams.

This paper proposes a novel scheme for a multi-way communication where users combine bi-directional multi-pair messages exchange with multi-directional multi-pair exchange. Particularly, we focus on the system where multiple users have multiple antennas exchange both private and common messages with each other. In this scheme, we can use simple zero forcing combined with successive network code decoding enables all user to decipher the encryption message from the relay despite the fact that they all have different self-information which they use as a key.

In this paper, a novel ultra-wideband (UWB) bandpass filter (BPF) based on multiple-mode resonator (MMR) is presented. The structure of the proposed MMR constructed by a modified triple-mode stepped-impedance resonator (SIR) loaded with a T-shape stub. This stub loaded resonator can generate two more resonate modes and two transmission zeros (TZs) simultaneously. Five resonate modes of the proposed MMR are roughly allocated in the UWB pass band, as well as two TZs at the lower and upper cut-off frequencies of the passband, leading to sharp roll-off. Using aperture-backed interdigital-coupled lines for feeding, passband is realized, first harmonic resonate mode (sixth mode) suppressed by first TZ of the interdigital-coupled lines, and upper stopband extended. Resonant modes and TZs are discussed together. Finally, the proposed filter is fabricated and measured, and predicted results verified in measurement.

In this paper, empirical relations for the evaluation of both the resonant frequency fr and the quality factor Q for the dominant TM₀₁₀ mode of a circular substrate integrated waveguide (SIW) cavity resonator are proposed and validated. These formulas are based on well established analytical expressions valid for the case of circular metallic cavity resonator, in which an equivalent radius R_eq, empirically derived, is employed. Their effectiveness is demonstrated by comparing the empirical predictions with the full wave results.

A dispersive conformal FDTD method has been proposed to accurately model the interface between two adjacent dispersive mediums and implemented to study the scattering of THz electromagnetic (EM) waves by inhomogeneous collisional plasma cylinder array. The method is based on the technology of area average, which is different from existing dispersive conformal FDTD schemes. Numerical results show that the proposed method enhance the accuracy level compared to the staircasing FDTD scheme involved in the inhomogeneous plasma. It is interesting to find that the THz EM waves can propagate through the plasma array more easily with higher frequencies or larger separations, hence the scattering width in the backward direction becomes smaller, and the forward scattering exhibits a little difference. This study will be useful for further designing intelligent plasma antenna arrays in THz band and terahertz reentry telemetry through plasma.

In this paper test study on low-cost civil engineering construction material is presented. In fact, in several civil constructions the strategy is to build up to first "fence" to EMI that limits interferences while using only in some limited areas high-cost ad hoc shielding material. The materials used in this study are tested at the Universita di Napoli Parthenope, formerly Istituto Universitario Navale (IUN) Reverberating Chamber (RC) according to a nested approach. Tests are made in the frequency range from 2 to 18 GHz and show that low-cost materials are able to achieve about 16 dB of shielding effectiveness (SE) in contrast to ad hoc materials that show about 50 dB in SE.

In this paper, band pass filters based on the microstrip configuration and utilizing coupled defected ground structures are presented. The 50 Ω microstrip line has a gap discontinuity in the middle and characterized by stepped impedance resonators on either half. The four fractal geometries tested for defected ground are the first and second iterations of the modified Moore curve, the closed staircase curve and a dual concentric closed staircase curve. The filters have a compact size and planar geometry. The modified Moore first iteration has a measured pass band from 2.27 GHz to 11.86 GHz, whereas the second iteration has a measured pass band from 1.85 GHz to 6.71 GHz. The measured pass band of the closed staircase is from 2.38 GHz to 7.21 GHz. The dual-concentric closed-staircase DGS filter offers a dual-band response with the measured pass band being from 2.41 GHz to 5.01 GHz and from 5.81 GHz to 8.35 GHz. All the filters are intended for UWB applications. A parametric study for the controlling parameters is also presented.

A passive millimeter-wave imager BHU-2D-U has been developed by Beihang University. This imager is designed for detecting concealed weapons on human body. It is a subsequent model of BHU-2D, which is also developed by the same group. In this paper, the improvements of BHU-2D-U over BHU-2D are introduced. Firstly, BHU-2D-U is used for whole body scan, which is different from BHU-2D. Thus, the field of view (FOV) of the new imager is enlarged and a new antenna array type is adopted. Secondly, the enlarged FOV requires smaller antenna spacing and compact receiver arrays. In order to reduce the volume of the receivers, I/Q demodulators operating in double side band mode are adopted because it does not need the image-reject filter, which is usually a bulky one. Thirdly, the quantity of the correlators increases because the number of receiving elements is doubled. To cope with the increase of the correlator quantity, a multiplexing technique is used in the FPGA internal layout of the correlator array unit. After a brief introduction, the system design and configuration is illustrated in detail. Finally, imaging experiments on a person with concealed weapon are conducted, by which the design and image reconstruction algorithms are verified. To conclude, initial results of BHU-2D-U have proved that the improvements are effective.

The one-step stair-shaped dielectric resonator antennas (DRAs)with a circular cross-section are studied theoretically and experimentally in this paper. The reasons why the one-step stair-shaped DRA shave a wideband performance have been investigated. It is shown in this paper that the modes excited in the one-step stair-shaped DRA with circular cross-section can be regarded as pseudo HEM₁₁₁ and pseudo HEM₁₁₃ modes. The pseudo HEM₁₁₁/ HEM₁₁₃ mode exhibits similar radiation patterns but a different resonant frequency and radiation Q factor to the HEM₁₁₁/ HEM₁₁₃ mode of the cylindrical DRA. By properly choosing the dimensions of the one-step stair-shaped DRA, the two modes can be used to obtain a wideband antenna.

A mathematical investigation of a normal mode helical antenna (NMHA) is presented to provide an equivalent model. The vector potential of a single-turn NMHA using a developed helix line is first derived. To avoid complexity in the vector potential, a useful relationship between the source point and the helix line is established. Employing this relationship, the integral of the vector potential can be calculated as that of a linear current antenna, and the result leads to an equivalent model that is a combination of the electric dipole and the magnetic dipole, i.e., exactly the same as assumed in previous work. A helix line of several turns can be regarded as a combination of the turns. Thus a general NMHA can be analysed as the sum of the vector potentials of the turns in the helix. To verify the obtained formulas, the calculated radiation characteristics are compared with the results of the commercial simulation, showing good agreement.

Two magnetless double-rotor (DR) dual-mode machines, namely the DR DCexcited multi-tooth switched reluctance (DR-DC-MSR) machine and the DR flux-switching DC (DR-FS-DC) machine, are proposed for special direct-drive applications where two rotating bodies are required to operate independently. Both machines can offer two different operation modes, namely the doubly-salient DC (DSDC) mode and MSR mode, normal and fault-tolerant operations, respectively. With the independent armature windings, both machines are able to couple their two rotors with two rotating bodies operating at various speeds. The proposed machines are designed and analyzed by using the time-stepping finite element method (TS-FEM). The simulation results confirm the validity of the proposed machines.

In this paper, a novel self-complementary shaped multiple-L slot loaded suspended microstrip patch antenna stacked with a polycrystalline silicon (poly-Si) solar cell is presented for 2.4/5.2 GHz band WLAN and 2.5/3.3/5.8 GHz band WiMAX networks. While the proposed self-complementary shaped multiple-L slot loaded suspended patch enables the propagation of multiple TMmn modes to be present, the poly-Si solar cell works as an RF parasitic patch element in addition to its photovoltaic function. The proposed stacked solar antenna combination topology enables the radiating patch to be easily modified by slot-loading to achieve multiband resonance characteristics and the poly-Si solar cell to operate without being shaded by any RF components of the antenna ensuring an optimum solar operation performance.