Solutions of Maxwell's equations for electromagnetic fields inside a waveguide coated with chiral nihility metamaterial and having one axis fractal are presented in this paper. A two-dimensional line source placed at the center of the waveguide is taken as an excitation. Power of electromagnetic fields inside the waveguide is determined, and results are plotted for various fractal dimension values ranging from 1 < D ≤ 2, and thickness of the chiral nihility coating.

A hepta-band covering GSM850/900/1800/1900/ UMTS/LTE2300/LTE2500 handset antenna array is presented. The antenna array consists of two symmetric antenna elements, A T-shaped protruded ground(TP) and three slots. The antenna element consists of a feed strip and two radiation strips (RS1, RS2), which only occupies a planar size of 15×25 mm² and generates dual-mode resonances at λ/8 and λ/4. The three slots and T-shaped protruded ground are utilized to reduce mutual coupling. Different slots can adjust different frequency bands independently. The working mechanism of the three slots is analyzed based on S-parameters and surface current distributions. The measured S₁₁ and S₁₂ are lower than −6 dB and -15 dB in the working bands, respectively. The radiation patterns and diversity performance are presented.

In this paper, a simple-fed, low profile, 9×10 elements quasi-lumped planar antenna array is presented. The proposed resonator employs a quasi-lumped element resonator that uses interdigital capacitor (IDC) in parallel with a straight strip inductor shorted across the capacitor. The array elements were designed and then excited by a feed network of four coaxial probes situated at the bottom plane but separated from the ground plane using a plastic material. The entire array is divided into four sub-array lattices of 5×5 elements and excited by a coaxial probe located at the centre of the sub-arrays antenna structure, thus exciting the centre resonator who in turn excites the neighbouring elements via proximity coupling. The probes are connected based on Wilkinson power divider principle to provide in-phase excitation. An explicit method is introduced to quickly obtain the array factor (AF) characteristics for such proximity coupled rectangular planar array. Radiation pattern and the array factor are presented, and are further compared with those obtained by the simulation and experimental results. The proposed antenna comprises 9×10 elements array, each of which is 5.8×5.6 sq. mm in size, and the entire antenna structure is about 120×80 sq. mm.

The scattering of an obliquely incident H-polarized plane electromagnetic wave by a magnetized plasma column is studied. It is assumed that the column is located in free space and aligned with an external static magnetic field. The emphasis is placed on the case where the angular frequency of the incident wave coincides with one of the surface- or volume-plasmon resonance frequencies of the column. The spatial structures of the field and energy flow patterns in the near zone of the column are analyzed, and the location of the regions with a greatly enhanced magnitude of the timeaveraged Poynting vector is determined. It is shown that the sign reversal of the longitudinal energy-flow component that is parallel to the column axis can occur when passing across the boundary between the inner region of the column and the surrounding medium.

This paper deals with reciprocity relations derivation for a nonlinear, stationary, homogeneous and isotropic plasma-like medium in an external homogeneous magnetic eld. A special case of such a medium is the charge carriers collective in semiconductors. It is shown that the classical reciprocity relations will be valid even in the presence of nonlinearity, and they can be used for Hall magnetometer bias compensation.

A graded material structure is optimized for broadband radome application by using hybrid method in this paper. In the optimization, dynamic range ratio (DRR) of real permittivity and loss of material are taken into considerations. By using an analytical function, the optimization problem with the DRR constraint is converted to an unconstrained problem. The proposed hybrid method is a combination of trust region method (TRM) and genetic algorithm (GA). Firstly (TRM) is applied to optimize the dielectric constant distribution. Then the result of TRM is used as initial value of GA. GA is employed to improve the global property of the results provided by TRM. Because TRM has the advantage of fast searching speed and GA has the advantage of global property, the hybrid method has the feature of fast convergence speed. And the jitter property of GA permittivity distribution is moderated. The effectiveness of the hybrid is validated through the designs of two broadband radome walls. The minimum power transmission efficiency is 81.9% ranging from 1 GHz to 18 GHz for normal incidence.

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.