In the following, numerical and experimental results for a line-shaped argon plasma source over a wide range of gas pressure (2 Torr-50 Torr) and microwave power (200-800 W) are presented. The line-shaped plasmas have been generated in a rectangular Pyrex tube, 15 mm in height and 5 mm inner width, placed-in a linear slot made in the upper wide wall of a custom-made narrow rectangular waveguide. The microwave power is coupled to the discharge gas via the slot. The effects of the waveguide width, power level (electron density, and discharge tube insertion depth on the excited axial (along x) electric field profile and hence the uniformity of the produced plasmas are investigated numerically using commercial software CST Microwave Studio®, and charge coupled device (CCD) camera. Results showed that, a uniform line-shaped plasma is generated as waveguide width decreased to 58 mm, plasma density value <<n_res = 3.7 × 10¹¹ cm^-3, and discharge tube insertion depth = 0 mm. An optical emission spectroscopy study was also realized to deduce the relative density of argon species and electron excitation temperature Texc. In general, argon spectral lines intensity was increased enhanced markedly when microwave power increased, while the different lines showed different behavior as argon pressure increased. The electron excitation temperature Texc decreases with increasing argon pressure, but almost constant overall the whole plasma length.

A topology of high-frequency field intensity in the work area of a saddle-shaped coil for a nuclear qaudrupole resonance spectrometer was studied. With a view to determine magnetic field topology, a computational domain was created which is a model of a saddle-shaped coil physical structure. Finite element method was used to perform numerical simulation in COMSOL Multiphysics software. According to the results of calculations performed and the field maps obtained, the relative volume of coil work area was determined which makes 28.12% of its full volume. For such a volume the recommended size of samples under study is 12×18×10 mm³.

This paper reports a neural-network-based methodology to estimate the amount of moisture content in soil at L, S and C frequency bands. A multilayered artificial neural network, using the Levenberg-Marquardt algorithm, is used as the ANN model. The input training data comprise the measured values of dielectric constant of soil in the dry and moist states. Dielectric constant is measured using microwave free-space transmission technique. Measurement has been performed using Vector Network Analyzer (VNA), microstrip patch antenna and soil sample holder. One great advantage with this method is that there is no need to test the pH value of the soil sample, and hence all the associated pre-processing steps, such as drying, pulverizing, can be avoided.

In this paper, a very compact ultra-wideband (UWB) multiple-input-multiple-output (MIMO) antenna, with a high isolation and triple notched bands, is proposed. Its size is dramatically decreased to 30×26×0.8 mm³ on a cost-effective FR4 substrate. It consists of two rectangular printed monopole (PM) elements and a simple stepped ground stub to enhance wideband isolation. For two different rejected bands of the wireless local area network (WLANs) covering 5.15-5.35 and 5.72-5.825 GHz, four parasitic C-shaped split-ring resonators (PCSRR) are placed on either side of the feed line. By etching two inverted U-shaped slots on the center of the patch, the notched frequency at 4 GHz C-band (3.7-4.2 GHz) of satellite communication systems is obtained. The results of simulation and measurement prove a bandwidth of S₁₁<-10 dB and S₁₂<-21 dB over the whole band (3.1-11.2 GHz) excluding the three independently adjustable rejection bands. Hence, the proposed UWB MIMO antenna has a very small size, simple structure, higher isolation and three narrower notched bands which effectively save more useful frequencies. Moreover, it is a good candidate for wireless portable UWB MIMO applications.

A novel compact tri-band band-pass filter (BPF) with transversal signal interaction concepts, based on composite right/left-handed transmission lines (CRLH-TLs) resonator and parallel stepped impedance resonator (SIR), is presented. The main path is based on a dual-mode CRLH-TL resonator, which exhibits the first two passbands. The secondary path is a SIR, which contributes to the third passband and generates another transmission zero between the first and second passbands simultaneously. The proposed filter has been simulated, fabricated and measured. Both the simulated and measured results show that the filter has a high selectivity with a compact size as small as 0.18λ_g×0.12λ_g.

This paper presents dielectric resonator antennas (DRAs) as efficient energy harvesters in the microwaves regime. A single DRA and 1×3 array were used to build foundation profiles for DRAs as energy harvesters. The proposed structures were designed and fabricated to resonate around 5.5 GHz. The study examined different factors that affect the harvester power efficiency. The size of ground plane and coupling between dielectric resonator (DR) elements in an array were studied, highlighting their effects on the overall efficiency of the harvester for different incident polarizations. A 5×5 array was built based on the studied factors and tested numerically and experimentally. Measurements showed that energy absorption eciency as high as 67% can be achieved using an array of DR antennas.

This paper presents the design and experimental research of a high efficiency balanced frequency tripler in the whole Ka band incorporating compensation solder pads. An anti-parallel GaAs Flip-Chip varistor diode is applied in this frequency tripler. The frequency tripler has the advantages of low conversion loss, broadband and compact circuit size. Considering the parasitic parameters resulted by the actual pads of the nonlinear device, a compensation solder pad was developed and adopted. The conversion loss of the frequency tripler is 15 dB with variation of ±1 dB across the output frequency from 30 to 37.5 GHz. In experiment, the maximum output power of 5.8 dBm is obtained at 35.4 GHz with 3.8% conversion efficiency when the input power is 20 dBm, and the 3-dB operation band width is about 10 GHz, which shows a good agreement between the simulation results and the experimental results.

Rice husk and coal is an innovation in enhancing the microwave absorption properties of pyramidal microwave absorbers to be used in radio frequency anechoic chambers. An anechoic chamber consists of radar absorbing material (RAM) along its wall; floor and ceiling to eliminate unwanted reflections to create electromagnetically quite environment. To design the pyramidal microwave absorber, coal has been added to rice husk. This innovative material combination has been investigated to determine the best reflectivity performance of pyramidal microwave absorbers. In the commercial market, polyurethane and polystyrene are the most popular foam based material that has been used in pyramidal microwave absorber fabrication. Simulation tool that has been used is CST Microwave Studio. Simulation based comparison of rice husk and combination of rice husk plus coal is done in the frequency range of 0-20 GHz. Pyramidal microwave absorber has been tested using dielectric probe method and radar cross section method. Reflection loss performance is tested in the frequency range of 8.2 to 12.4 GHz.

During re-entry into earth's atmosphere, a spacecraft suffers from loss of communication with the ground control station, known as communication blackout, due to formation of plasma around the re-entry spacecraft. This paper presents the theory and analysis of the communication blackout and its mitigation using static magnetic field method. The interaction between electromagnetic waves and plasma in presence as well as absence of magnetic field is described to determine the effects of plasma sheath on the spacecraft re-entering into the atmosphere. An analysis is done to determine the effectiveness of this mitigation technique for a typical re-entry spacecraft and the strength of magnetic field required to establish the communication link between the re-entry spacecraft and the ground station is obtained.

In this paper, a new antenna is designed in order to use in the wireless capsule endoscopy (WCE) system. This antenna consists of two parts; the small monopole part and the small spiral. Having the omnidirectional radiation pattern for covering the stochastic motions of the capsule into gastrointestinal and also, appropriate gain and wide bandwidth to achieve high resolution images must be considered in designing procedure. In this design, a good radiation pattern is obtained from small monopole, and using the spiral structure leads to an appropriate wide bandwidth and a miniaturized antenna. By simulating this antenna in the human body environment and considering four different body tissues and their results, the antenna has the bandwidth of 360 MHz (39.3% relative bandwidth) at 928 MHz center frequency which covers the ISM band (868.0-868.6 MHz and 902.8 to 928.0 MHz). The radiation pattern of the antenna is omnidirectional. The maximum gain of the designed antenna is -23 dB, over the frequency band that is suitable for using as a transmitter antenna in the WCEs.

Agricultural waste is produced at agricultural premises as a result of an agricultural activity. Agriculture residue is made up of organic compounds from the living plants like rice straw, oil palm empty fruit bunch, sugarcane bagasse, coconut shell, banana leaves and others. This research has highlighted their eco-friendly nature and high microwave absorption properties, developing a new and improved form of pyramidal absorbers including high carbon content coal in it. Software simulation is done using CST Microwave studio. Samples are developed using a new technique by adding cobalt as an accelerator, and its performance is analyzed in terms of its reflection loss performance using free space measurement method in the frequency range of 8.2 to 12.4 GHz.

Based on gain optimization methods, superdirective beamformers can achieve high beam directivity with small aperture array. However, the extreme sensitivity to array uncertainty is a main obstacle to engineering application. In this work, a robust gain optimization algorithm under uncertainty set constraint is proposed. Considering steering vector mismatch is the result of combined effect of various array errors, and it is a measurable indicator especially in receiving system. We apply its uncertainty as a constraint on gain optimization method, which is more intuitive in physical sense. Different from existing solutions, it makes a better tradeoff among directive gain, robustness and radiation efficiency. Experimental analysis verifies its good performance in engineering.

The pattern synthesis for large antenna arrays is very important because of its wide applications. Several antenna array synthesis techniques for planar antenna array have been developed in the past years. In this paper, a hybrid method for solving antenna array pattern synthesis problem is introduced. The proposed method has three steps. Firstly, the iterative fast Fourier transforms (IFT) is used to generate a number of initial array excitations based on aim pattern. Then, the global optimization method differential evolution strategy (DES) is used to optimize these excitations based on initial excitations. After that, if the optimized pattern does not satisfy the goal, the simulated annealing (SA) method is applied to optimize the excitations until the goal is achieved or the maximum iteration is reached. Several simulation results show that the desired pattern can be effectively synthesized by using the proposed method.

A broadband via-hole less transition from a conductor-backed coplanar waveguide (CBCPW) to a parallel coupled microstrip line (CMS) via microstrip section (MS) is reported in this paper that is realized on a MCL FX-2 substrate (100 μm thick). This transition should find a wide variety of applications due to its demonstrated broadband (from 4.5 GHz up to 39.5 GHz) behavior, ease of fabrication, and low manufacturing cost. In addition, utilization of the MS section between the CBCPW and CMS sections allows putting ground electrode in a different plane than the signal electrodes. This exibility made possible by electromagnetic field coupling between the bottom and top ground planes simplifies the transition manufacturing and facilitates the characterization of optical components driven with CMS line using coplanar probes.

This paper examines the feasibility of LTE-based passive radar for detecting ground moving targets. Specifically, the focus of this paper is to describe the proposed LTE-based passive radar system and to conduct an experiment using a real LTE eNB transmitter as an illumination source. Seven scenarios were carried out to investigate the detection performance of the proposed system on ground moving targets with different speeds, trajectories and range. In addition, multi-target detection was also tested. The experimental results showed that the LTE-based passive radar system has the capability to detect typical ground targets/objects like cars, motorbikes and humans moving at different trajectories. The positive results opened up a new frontier for passive radar systems to be used in many potential applications, including security, border protection, microwave fences, monitor of buildings and others.

Fractional slots concentrated windings (FSCWs) are characterized with high magnetic motive force (MMF) harmonics which results in undesirable effects on permanent-magnet (PM) machines. A new design technique is reported in this paper in order to simultaneously reduce the sub- and high MMF harmonics. By using multiple layer windings and different turns per coil, a new 18-teeth/10-poles FSCWs PM machine is designed. Then, this machine is evaluated as compared with a conventional 12-teeth/10-poles FSCWs PM machine. Both machines are designed under the same electrical and geometrical constrains. The obtained results verify the high performances of the newly designed machine. Due to the adopted new winding type, the proposed design can effectively reduce eddy current loss in PMs as compared with the conventional design.

A compact omnidirectional vertical-polarized broadband slot antenna for indoor distributed antenna systems is presented. The proposed antenna consists of a deformed printed monopole on one side of the substrate and a polygon slot in the circular ground plane on the other side. Due to the utilization of the wideband slot structure, the antenna achieves small electrical dimension of 0.327λ×0.327λ×0.0046λ at the lowest operating frequency, and an impedance bandwidth of about 129% (0.66-3.07 GHz) for VSWR≤1.5 is achieved, covering all frequency bands for 2G, 3G, 4G and some Wi-Fi communications. The proposed antenna has stable radiation patterns over the operating bands. The measured gains of the antenna range from 1.5 dBi (lower band) to 5.5 dBi (higher band). Compact planar structure makes the proposed antenna a perfect candidate for ceiling or surface mounted indoor distributed antenna applications.

In this study, a dumbbell-shaped metamaterial (MTM) antenna has been proposed for dual-band applications using finite difference time domain (FDTD) technique. Such a composite MTM antenna consists of dumbbell-shaped patch, microstrip and partial ground plane. The proposed antenna shows dual-band behavior having impedance bandwidths (|S₁₁| < -10 dB) of 28.5% and 8.7% at 1.72 GHz and 3 GHz respectively. It has been designed to operate at various cellular standards such as GPS, GSM1800 and WCDMA. Design and analysis have been carried out using FDTD code based on uniform meshing and convolutional perfectly matched layer (CPML) absorbing boundary conditions. Further, simulation results have been verified using HFSS, and a prototype has been fabricated to validate the results experimentally. The overall electrical size of the proposed antenna is 0.287λ_o × 0.346λ_o × 0.009λ_o. The proposed dual-band antenna offers excellent radiation characteristics with a gain of 1.2 dBi and 1.5 dBi at 1.72 GHz and 3 GHz respectively with omnidirectional radiation patterns in xz-plane.

A compact multiband bow-tie dipole slot antenna fed by coplanar waveguide (CPW) is proposed in this paper. Multiple resonant mode technique and notch-band technique have been combined in this design to form triple-band operation just by adding single elements. Based on this, a pair of hairpin-shaped branches is implemented on each arm of the bow-tie slot antenna. A notch-band property is achieved compared with the original wideband bow-tie antenna (without branches). Meanwhile, a new lower resonant frequency is obtained by using this kind of structure, which means the size is compact in nature and the triple-band operation is achieved. The notch-band and lower resonant frequency can be tuned by changing the length of the branch. The parameters of the antenna, including reflection coefficients, current distributions, radiation patterns and gain, are achieved by numerical simulations and measurements. The results indicate that the slot size of the proposed antenna is 52.4 mm×22.3 mm, and the proposed antenna can offer triple-band operation at 2.39-2.50 GHz (4.5%), 3.38-3.79 GHz (11.4%) and 4.87-6.23 GHz (24.5%), which is suitable for WLAN in the 2.4/5.2/5.8-GHz bands and WiMAX in the 3.5/5.5-GHz bands.

Novel compact dual-band branch-line couplers are presented. By using ahalf elliptical-ring impedance stub as a basic unit, dual-band branch-line couplers are obtained. Sincea couple of half elliptical-ring impedance stubs can be folded inward to its enclosed areawithout overlap, the branch-line couplercan be miniaturized. In order to verify the effectiveness of the half elliptical-ring impedance stub, two different branch-line couplers operating at 2.4/5.8 GHz are designed, fabricated and tested. Measured results agree well with simulated ones. Compared with the stepped-impedance-stub branch-line couplers, sizes of the proposed couplers are reduced by 43% and 30%, respectively.