Scielo RSS <![CDATA[Journal of Microwaves, Optoelectronics and Electromagnetic Applications]]> vol. 16 num. 2 lang. es <![CDATA[SciELO Logo]]> <![CDATA[A JL-SDR-IMPATT Device with Improved Efficiency]]> Abstract An attempt has been made to present a new device which will function as a highly efficient SDR (Single Drift Region) P+-N- N+ IMPATT diode utilizing the advantages of a junctionless field effect transistor. The basic idea is to convert a uniform N+ region into a (P+-N-N+) structure without any requirement of physical doping. As the present device works on the principle of a junctionless channel, variability and short channel effects are significantly reduced as compared to the conventional TFET though the requirement of an extra gate increases a few fabrication steps. Further, efficiency more than conventional SDR IMPATT diode is achievable without any physical doping. <![CDATA[Design of a Compact UWB Bandpass Filter using Via-Less CRLH TL]]> Abstract A novel compact ultra wideband (UWB) bandpass filter (BPF) based on composite right/left handed transmission line (CRLH TL) is reported in this paper. The proposed UWB BPF is designed and developed by coupling of two unit-cells of via-less CRLH TL, excited by asymmetrical coplanar waveguide (CPW) feed-line. The unit cell of CRLH TL is designed using series interdigital capacitor (IDC) in shunt with the shorted inductive stub. Because of the CPW-fed, no via is required to get the shunt inductance for the realization of CRLH TL, which minimizes the fabrication steps. The filter is compact in size 11. 9 × 6 mm2. The proposed filter exhibits the return-loss (|S11|) more than 11. 2 dB and insertion-loss (|S21|) less than 0. 5 dB and low and flat group delay response throughout the passband, 3. 3 GHz to 13. 0 GHz. The proposed UWB BPF also shows the good stopband rejection (|S21| &gt; 20 dB and |S11| &lt; 0. 8 dB) from 13. 6 GHz to 15 GHz and steep roll-off from passband to stopband. The fractional bandwidth (FBW) of the filter is found to be 119 %. The equivalent lumped circuit model of the filter is obtained through Ansoft Designer. All simulated results are extracted through method of moment based simulator, IE3D. Agilent vector network analyzer (VNA) is used to get the measured results. All measured results are found in close similarity with the simulated results. <![CDATA[Circuit models of Lossy Coaxial Shielded cables to Analyze Radiated and Conducted Susceptibilities with unmatched line loads]]> Abstract This paper presents a circuit models to analyze the variation effects of incident plane wave on shielded coaxial cables, using Branin's method, which is called the method of characteristics. The model can be directly used for the time-domain and frequency-domain analyses and for all arbitrarily loaded. This makes it easy to insert in circuit simulators, such as SPICE, SABER, and ESACAP. The obtained results are in good agreement with those from others methods. Finally, we will discuss the effects of the variation of the incident plane wave. <![CDATA[Broadband Equal Power Divider]]> Abstract This paper presents the design of broadband two way equal power divider in microstrip medium with defected ground structure suitable for broadband communication systems. Quarter wave broadside coupled lines are used in the place of conventional transformers widely used in the popular Wilkinson power dividers. The proposed power divider structure takes the advantage of top and bottom layers of the microstrip medium to create broadside coupled line configuration using defected ground plane. The floating conductor in the bottom layer plays a critical role in achieving the band select characteristics. Experimental results of two way equal power divider designed using the proposed structure has been verified against the full wave simulations. The isolation between the paths is more than 20dB and the return loss at each port is better than 15dB across the desired band of 3GHz to 8GHz. <![CDATA[Optimization of Frequency Selective Surfaces with Crossed Dipoles Using the Taguchi's Method]]> Abstract There are several techniques for optimization of Frequency Selective Surfaces (FSS). Generally, in literature, we can find a few articles about the Taguchi's method applied in electromagnetic. This method is based on orthogonal arrays (OAs) and it is a procedure that reduces the number of iterations required in an optimization process. For a FSS optimization using the crossed dipole geometry, the Taguchi's method, in combination of the equivalent circuit method, is used for the first time. Here, we applied the method for synthesis of FSS with crossed dipole geometry. The results show that the parameters, of the synthesized FSS, are extracted in an easy and successful way. A prototype was built for validation purpose. <![CDATA[Influence of temperature on the refractive index sensitivities of fiber Bragg gratings refractometers]]> Abstract Effect of cross-sensitivity between temperature and refractive index (RI) was studied using an optical sensor based on Bragg grating inscribed in an etched multi-mode fiber (MMF). RI sensitivities of different modes were used to obtain a linear response and temperature dependence in water:glycerin solutions. Results pointed out that the absolute average RI sensibility reduces from 0.97 ± 0.05 nm/RIU to 0.76 ± 0.07 nm/RIU while the temperature increases from 15 °C up to 35 °C, respectively. Effect of temperature on the RI sensitivity is related with the increasing difference between the fiber and surrounding RI, which results in lower evanescent field and, consequently, reduced surrounding RI sensitivity. Therefore, in order to improve the precision during the RI measures, the effect of temperature must be considered in the calibration curves, principally in MMF fiber grating sensors that show low RI sensitivity values. <![CDATA[Substrate Integrated Waveguide (SIW) Bandpass Filter with Novel Microstrip-CPW-SIW Input Coupling]]> Abstract A Substrate integrated waveguide bandpass filter is presented with a novel CPW-to-SIW transition at both the input and output ports which also served as the input and output couplings into the filter. The CPW-to-SIW transition structures presented here exploited the step impedance between the 50 ohms input/output feedline and the transition to control the input/output couplings of the filter. The SIW filter is also shown to have very minimum milling or etching requirement which reduces the fabrication error. The proposed SIW filter has been validated experimentally and results presented. The results show that a simulated return loss of 15 dB and an initial measured return loss of 16 dB were achieved. An improved measured return loss of 22 dB was later achieved after some tuining adjustments were performed on the filter input and output couplings. A minimum insertion loss of 1.3 dB was also achieved across the band. <![CDATA[Experimental and numerical investigation of the microwave dielectric properties of the MgTiO<sub>3</sub> ceramic matrix added with CaCu<sub>3</sub>Ti<sub>4</sub>O<sub>12</sub>]]> Abstract This paper describes an experimental and numerical investigation of the dielectric resonators based on the MgTiO3 ceramic matrix, which relates to their dielectric properties in microwave. The resonators are compounds of the MgTiO3 added with 4, 6, 8, 10 and 12 wt% of the CaCu3Ti4O12. The manufacturing process of the resonators is based on the solid-state method. The properties of the permittivity and dielectric loss are elucidated using the Hakki and Coleman´s method. The experimental measurements of the dielectric resonators, acting as antennas, provide some results as return loss, gain, efficiency, bandwidth and input impedance. These results are coherent with the numerical investigation. The addition of the perovskite CaCu3Ti4O12 in the MgTiO3 ceramic matrix increased the value of the dielectric constant and it was obtained a higher value of 21.01 for the sample MgTiO3 added with 12% CaCu3Ti4O12. The temperature coefficient of resonant frequency (τf) was measured for all the samples and the best value obtained was 9.62 ppm/°C for the sample MgTiO3 added with 12% CaCu3Ti4O12. The material duly proposed, shows to be promising for applications as dielectric antennas and this study point out that it is possible to obtain a dielectric resonator antenna (DRA) with a temperature coefficient of resonant frequency close to zero. <![CDATA[A CPW-Fed Structure Shaped Substrate Wideband Microstrip Antenna for Wireless Applications]]> Abstract A structure shaped substrate wideband microstrip patch antenna fed by coplanar waveguide (CPW) is proposed for wireless applications. Structure shaped substrate is produced by cutting the rectangle shape substrate in the form of a semicircular disc. The radiating patch of proposed antenna is taken in the form of U-shape. The ground plane is extended towards both sides of radiator for reducing the size of the antenna. The proposed antenna is simulated by Ansoft's High Frequency Structure Simulator (HFSS). A good agreement is observed between simulated and measured results. The prototype is taken with dimensions 24 mm × 24 mm ×1.6 mm that achieves wide bandwidth, constant group delay and good radiation patterns over the entire operating bandwidth from 3.4 to 9.4 GHz (6.0 GHz) with 93.7% impedance bandwidth at 6.4 GHz center frequency. Thus, the proposed antenna is applicable for C band applications. <![CDATA[The force magnitude of a human bite measured at the molar intercuspidation using fiber Bragg gratings]]> Abstract This study describes a localized method – using optical fiber Bragg gratings (FBGs) – to determine the human bite force at the very moment of occlusion, in maximum intercuspidation. The FBG was encapsulated in a silicone splint between uppers and lowers first molars and avoiding pre-contact with the other teeth in a dentition model. Gypsum dental castings of two volunteers are performed in a semi-adjustable articulator in the occluded situation to maintain angulations of the occlusal plane within normal occlusion. The sensor was characterized in vitro for both volunteers and the human bite force is measured in vivo. The orthodontic forces on the sensor are acquired at four moments: before of occlusion (free situation), occlusion, biting and maximum bite. The measured maximum bite forces are 85 N for female (brachyfacial) volunteer and 76 N for male (mesofacial) volunteer, between right uppers and lowers first molars. The difference can be associated to the facial pattern. The results obtained show the possibility to employ the optical encapsulated sensor to perform measurements of orthodontic forces in order to analysis different types of facial patterns with minimum of interference at occlusion. <![CDATA[Analysis of Thermo-Mechanical Stress in Fiber Bragg Grating Used for Hydro-Generator Rotor Temperature Monitoring]]> Abstract Fiber Bragg gratings (FBGs) offer new possibilities to monitor accurately the rotor temperature. Dozens of sensors can be mounted in series in a single fiber and used to measure the temperature in several points of the rotor winding. Such sensors installed directly on the rotor winding surface are thermally isolated from the cooling air by a silicone layer. Because of the temperature gradient in this structure, the sensor is exposed to thermo-mechanical stresses and therefore can be deformed. Since the FBG probes are sensitive to both temperature and strain, the knowledge of each effect separately is necessary to ensure that the temperature readings are not affected by strain. Experimental results obtained in rotor winding mockup tests with thermistors and FBG sensors show that the temperature readings by the FBG are 4.5°C above the temperature defined by the thermistors which were used as references. Multi-physics simulations were carried out to calculate the strain and temperature in the FBG assembly. The theoretical and experimental results are in a good agreement. <![CDATA[Design of Microstrip Antenna Array with Suppressed Back Lobe]]> Abstract A practical procedure to reduce the back lobe level of linear microstrip antenna arrays is presented in this paper. The novel concept consists in the design of the radiators asymmetrically positioned with respect to the ground plane. In order to validate this technique, a four-element linearly-polarized array is designed in the HFSS software and a prototype is manufactured. Furthermore, the design of beamforming circuit to achieve broadside radiation and -20 dB side lobe level is detailed. Very good agreement between simulated and experimental results is obtained. Although the technique is presented for linearly polarized arrays, it is general and can also be applied in the circularly polarized ones. <![CDATA[Experimental Evaluation of the Mobile Radio Channel Capacity in the 2.48 GHz Band]]> Abstract This paper deals with the effect of the Single-Input Multiple-Output spatial diversity on the OFDM mobile radio signal propagating in an urban channel. From measurements performed in Rio de Janeiro city, Brazil, by using two receiving antennas at diversity, the calculated capacity presented an improvement when compared to the individual one. <![CDATA[Spectrum Continuity and Contiguity based Dedicated Protection for Flexible Optical Networks]]> Abstract Elastic optical networks (EONs) have been pointed out as a promising candidate for transporting data with high transmission rates in adaptive optical networks. Consequently, the occurrence of a failure in a simple element may cause the interruption of various services. Survival mechanisms have been crucial to try to overcome the problems created by possible failures. In this paper, we propose a new dedicated path protection mechanism for link-failure survivability in EONs, referred to as Spectrum Continuity and Contiguity based Dedicated Protection (SCCDP). SCCDP tries to avoid the trap topology problem in search for a link-disjoint route pair. In addition, the calculation of the link-disjoint routes is based on modified version of the Dijkstra's algorithm, referred to as Spectrum Continuity and Contiguity based Shortest Path (SCCSP), which chooses the pair of routes according to the end-to-end spectrum continuity and contiguity. The performance of the proposed algorithm is compared to other well-known algorithms in the Literature. Two different network topologies are used in our simulations for comparison purposes. Our proposal achieved better results concerning blocking probability. <![CDATA[Investigation of Dosimetry in Four Human Head Models for Planar Monopole Antenna with a Coupling Feed for LTE/WWAN/WLAN Internal Mobile Phone]]> Abstract The objective of the present study is to evaluate the Specific Absorption Rate (SAR) within the human head model exposed to the radiation of planar monopole antenna with T-shaped coupling feed and an inductive shorting strip. The presented design has a compact structure, a planar configuration and occupying a small size of 36×20mm2. Two wide bands can be generated by the proposed antenna 546 MHz (734-1280 MHz) and 1066 MHz (1934-3000 MHz) for the LTE/WWAN/WLAN internal mobile phone. The antenna performance parameters comprising return loss, radiation patterns, and gain are discussed. In this research work four different human head models have been implemented: homogenous spherical head, spherical seven layer model, Specific Anthropomorphic Mannequin (SAM) phantom and HUGO human head model. On the other hand the effects of operating frequency and gap distance between the mobile phone antenna and the human head model on distributions of the SAR inside the human head are investigated. All the simulations are done for three different distances between the antenna and the head model (5 mm, 10 mm and 20 mm). Moreover, the SAR levels for the head tissues are calculated in accordance to the two currently accepted standards: Federal Communications Commission (FCC) and International Commission on Non-Ionizing Radiation Protection (ICNIRP). <![CDATA[A Compact Ultrathin Ultra-wideband Metamaterial Microwave Absorber]]> Abstract A simple design of compact ultra-wideband, ultra-thin metamaterial microwave absorber has been presented. The unit cell of the proposed design is composed of diagonally placed ‘microstrip bend’ like patches printed on grounded dielectric substrate. The simulation results demonstrate the 10-dB absorption bandwidth of 7.19 GHz from 10.45 GHz to 17.64 GHz and FWHM (full width at half maximum) bandwidth of 11.43 GHz from 9.61 GHz to 21.04 GHz. The proposed design presents more than 90% absorption for a bandwidth of 1.02 GHz at wide angle of incidence up to 60°. The absorption mechanism has been analyzed through surface current and electromagnetic field distributions. The proposed design has been fabricated and experimentally tested for its 10-dB absorption bandwidth under different polarization and oblique angles of incidence of electromagnetic wave. The designed absorber is low profile (unit cell size is ~0.257 λ0 at the center frequency corresponding to 10-dB absorption bandwidth), ultrathin (~λ0/14 thick at the center frequency) and provides a novel design of wideband absorber for many useful applications. <![CDATA[ANALYTICAL METHOD FOR DESIGNING FSS-BACKED REFLECTARRAY ANTENNA USING TRANSMISSION LINE APPROACH]]> Abstract The main purpose of this paper is introducing a new method based on the transmission line approach for designing FSS-backed reflecarray antennas. For this reason a dual band reflectarray antenna is designed. This antenna contains a conventional single layer RA and a FSS backed double layer RA with 54% and 50% efficiency operating at X band and K band, respectively. A double layer FSS is used between RAs to isolate them. K band cell element is designed and analyzed using transmission line method and consideration of equivalent circuit for elements of each layer. Then the results obtained using this technique is compared to those found by CST and ADS. The comparison shows a good agreement. Jerusalem cross dipole with variable size is employed as radiation element in both bands. The most important properties of our suggested array are low cross polarization and high efficiency. <![CDATA[Compact MIMO Antenna for Multiband Mobile Applications]]> Abstract This paper presents a multiple input multiple output (MIMO) antenna for multiband operation based on meander lines with L shaped metallic strip. Meander lines is basically a monopole antenna loaded with multiple sections of short circuited transmission line that acts as inductor and alter the impedance characteristics of antenna. Antenna size miniaturization of 69 % has been achieved by placing double U slots on the ground plane and a line slot DGS (Defective Ground Structure) is used to reduce the mutual coupling between the antenna elements. The values of envelope correlation coefficient (ECC) and Specific Absorption Rate (SAR) lie well below the specified limit. <![CDATA[A Novel Simple Convoluted Geometry to Design Frequency Selective Surfaces for Applications at ISM and UNII Bands]]> Abstract In this paper, we use a novel convoluted geometry to design a dual-band FSS with angular stability and independent polarization operation. The geometry allows the design of a dual-band FSS to block ISM and UNII radio bands. We performed a parametric study with the commercial software ANSYS HFSS. A prototype of our proposed FSS design was built and its transmission characteristics were measured and compared with simulated results. We observed good agreement between numerical and experimental results. The proposed FSS realized a dual-band response at the required bands and it had angular stability and polarization independence. <![CDATA[A Compact Dual-Band CPW-Fed Planar Monopole Antenna for 2.62–2.73 GHz Frequency Band, WiMAX and WLAN Applications]]> Abstract In this paper, we present a compact and low-profile monopole antenna with a simple structure for the 2.6–2.73 GHz frequency band, the Worldwide Interoperability for Microwave Access (WiMAX) and the Wireless Local Area Network (WLAN) applications. The first configuration of our antenna mainly consists by three radiating elements: inverted L-shaped Stub1, L-shaped Stub2 and a rectangle Stub3. By adjusting the lengths of the three Stubs, three resonant frequencies can be achieved and adjusted separately. Then, the assembled between Stub2 and Stub3 gives the final design of our proposed antenna with a small overall size of 20 mm × 37 mm × 1.56 mm. From the experimental results it is observed that, the antenna prototype has achieved two operating bandwidths (S11≤ -10 dB): the first band from 2.62 to 2.73 GHz (110 MHz) and a second broadband from 3.02 to 7.30 GHz (4280 MHz) which combines WiMAX and WLAN applications. The antenna also exhibits an almost omnidirectional radiation patterns over the operating bands. The parameters which affect the performance of the antenna in terms of its frequency domain characteristics are studied in this paper. The details of the monopole antenna design along with simulated and experimental results are presented and discussed. <![CDATA[Analysis of Linear Antenna Array for minimum Side Lobe Level, Half Power Beamwidth, and Nulls control using PSO]]> Abstract This paper presents the optimization performance of non-uniform linear antenna array with optimized inter-element spacing and excitation amplitude using Particle Swarm Optimization (PSO). The aim of the proposed algorithm is to obtain the optimum values for inter-element spacing and excitation amplitude for a linear antenna array in a given radiation pattern with suppressed Side Lobe Level (SLL), minimum Half Power Beamwidth (HPBW), improved directivity and placement of nulls in the desired direction. A variety of design examples are considered and the obtained results using PSO are validated by benchmarking with results obtained using other nature-inspired meta-heuristic algorithms such as the Real-coded Genetic Algorithm (RGA) and the Biogeographic Based Optimization (BBO) algorithm. The comparative results are shown that optimization of linear antenna array using the PSO provides considerable enhancement in the SLL, the HPBW, the directivity and the null control in the desired direction. <![CDATA[A Compact UWB Monopole Antenna with Rejected WLAN Band using Split-Ring Resonator and Assessed by Analytic Hierarchy Process Method]]> Abstract The design of a compact microstrip line-fed Ultra-wideband (UWB) monopole antenna with a notched band characteristic is presented in this paper. The rejection frequency band occurs around 5-6 GHz, which is appropriate for wireless local area network (WLAN) applications and is obtained by a split-ring resonator on the antenna ground plane. The proposed antenna is printed on FR4 substrate material with a dielectric constant of 4.4. The dimension of the proposed antenna is 24×16×0.8 mm3. Radiating patch has a combined geometry realized by a half-circular ring and half-square ring. To achieve a proper impedance matching and increased bandwidth with VSWR ≤ 2, the study made use of an L-shaped element which was connected to the ground plane; moreover, the researchers added a split-ring resonator onto the ground plane to obtain one notched band. The comparison of the proposed antenna performance with previously presented UWB monopole antennas, was performed by using Analytic Hierarchy Process method. A good agreement was observed between simulated and experimental results.