International Journal of Microwave Science and Technology The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Characterization of and Permittivity of Solid Material of NiO, ZnO, , and at Microwave Frequency Using Open Ended Coaxial Probe Sun, 29 Nov 2015 14:16:56 +0000 This paper describes a detailed study on the application of an open ended coaxial probe technique to determine the permittivity of in the frequency range between 1 GHz and 10 GHz. The compositions of the spinel ferrite were 0.1, 0.3, 0.5, 0.7, and 0.9. The samples were prepared by 10-hour sintering at 900°C with 4°C/min increment from room temperature. Particles showed phase purity and crystallinity in powder X-ray diffraction (XRD) analysis. Surface morphology measurement of scanning electron microscopy (SEM) was conducted on the plane surfaces of the molded samples which gave information about grain morphology, boundaries, and porosity. The tabulated grain size for all samples was in the range of 62 nm–175 nm. The complex permittivity of Ni-Zn ferrite samples was determined using the Agilent Dielectric Probe Kit 85070B. The probe assumed the samples were nonmagnetic homogeneous materials. The permittivity values also provide insights into the effect of the fractional composition of on the bulk permittivity values . Vector Network Analyzer 8720B (VNA) was connected via coaxial cable to the Agilent Dielectric Probe Kit 85070B. Fahmiruddin Esa, Zulkifly Abbas, Fadzidah Mohd Idris, and Mansor Hashim Copyright © 2015 Fahmiruddin Esa et al. All rights reserved. Turn Ratio, Substrates’ Permittivity Characterization, and Analysis of Split Ring Resonator Based Antenna Tue, 03 Nov 2015 11:45:28 +0000 The turn ratio, coupling space between sections, and substrate permittivity effects on spilt ring resonator (SRR) are investigated. The analysis of the presented SRR with respect to the effects of substrate and number of gaps per ring to further characterize its peculiarities is experimented with miniaturized capability as our intent. Six different SRRs were designed with different turn ratios, and the sixth is rectangular microstrip patch centre-inserted. Different numbers and gap sizes are cut on the SRRs while the gap spacing between the conductors of the SRR was varied to determine their effects taking cognizance of the effects of different substrates. The designs were investigated numerically using 3D finite integration technique commercial EM solver, and the resulting designs were prototyped and subsequently measured. Findings indicate that the reflection coefficient of the MSRR with centre-inserted patch antenna is better compared to MSRR without the patch antenna irrespective of the laminate substrate board, and so is its gain. Seyi S. Olokede, Nurul A. Mohd-Razif, and Nor M. Mahyuddin Copyright © 2015 Seyi S. Olokede et al. All rights reserved. Design of UWB Planar Monopole Antennas with Etched Spiral Slot on the Patch for Multiple Band-Notched Characteristics Tue, 20 Oct 2015 11:04:19 +0000 Three types of Ultrawideband (UWB) antennas with single, double, and triple notched bands are proposed and investigated for UWB communication applications. The proposed antennas consist of CPW fed monopole with spiral slot etched on the patch. In this paper single, double, and also triple band notches with central frequency of 3.57, 5.12, and 8.21 GHz have been generated by varying the length of a single spiral slot. The proposed antenna is low-profile and of compact size. A stable gain is obtained throughout the operation band except the three notched frequencies. The antennas have omnidirectional and stable radiation patterns across all the relevant bands. Moreover, relatively consistent group delays across the UWB frequencies are noticed for the triple notched band antenna. A prototype of the UWB antenna with triple notched bands is fabricated and the measured results of the antenna are compared with the simulated results. Swarup Das, Debasis Mitra, and Sekhar Ranjan Bhadra Chaudhuri Copyright © 2015 Swarup Das et al. All rights reserved. Logarithmic Slots Antennas Using Substrate Integrated Waveguide Mon, 19 Oct 2015 06:14:44 +0000 This paper represents new generation of slotted antennas for satellite application where the loss can be compensated in terms of power or gain of antenna. First option is very crucial because it totally depends on size of satellite so we have proposed the high gain antenna creating number of rectangular, trapezoidal, and I shape slots in logarithm size in Substrate Integrated Waveguide (SIW) structure. The structure consists of an array of various shape slots antenna designed to operate in C and X band applications. The basic structures have been designed over a RT duroid substrate with dielectric constant of 2.2 and with a thickness of 0.508 mm. Multiple slots array and shape of slot effects have been studied and analyzed using HFSS (High Frequency Structure Simulator). The designs have been supported with its return loss, gain plot, VSWR, and radiation pattern characteristics to validate multiband operation. All the proposed antennas give gain more than 9 dB and return loss better than −10 dB. However, the proposed structures have been very sensitive to their physical dimensions. Jahnavi Kachhia, Amit Patel, Alpesh Vala, Romil Patel, and Keyur Mahant Copyright © 2015 Jahnavi Kachhia et al. All rights reserved. Design of a Novel Ultrawide Stopband Lowpass Filter Using a DMS-DGS Technique for Radar Applications Thu, 15 Oct 2015 13:31:53 +0000 A novel wide stopband (WSB) low pass filter based on combination of defected ground structure (DGS), defected microstrip structure (DMS), and compensated microstrip capacitors is proposed. Their excellent defected characteristics are verified through simulation and measurements. Additionally to a sharp cutoff, the structure exhibits simple design and fabrication, very low insertion loss in the pass band of 0.3 dB and it achieves a wide rejection bandwidth with overall 20 dB attenuation from 1.5 GHz up to 8.3 GHz. The compact low pass structure occupies an area of (0.40  × 0.24) where = 148 mm is the waveguide length at the cut-off frequency 1.1 GHz. Comparison between measured and simulated results confirms the validity of the proposed method. Such filter topologies are utilized in many areas of communications systems and microwave technology because of their several benefits such as small losses, wide reject band, and high compactness. Ahmed Boutejdar, Ahmed A. Ibrahim, and Edmund P. Burte Copyright © 2015 Ahmed Boutejdar et al. All rights reserved. An Iterative Approach to Improve Images of Multiple Targets and Targets with Layered or Continuous Profile Sun, 27 Sep 2015 06:15:26 +0000 An iterative approach, based on the linear sampling method (LSM) and the contrast source inversion (CSI) method, is proposed to improve the recovered images of multiple targets and targets with layered or continuous profile, including shape and distribution of electric properties. The difficulties in dealing with large targets or high contrast are partly overcome with this approach. Typical targets studied in the literatures are chosen for simulations and comparison. Yu-Hsin Kuo and Jean-Fu Kiang Copyright © 2015 Yu-Hsin Kuo and Jean-Fu Kiang. All rights reserved. Novel Notched UWB Filter Using Stepped Impedance Stub Loaded Microstrip Resonator and Spurlines Thu, 17 Sep 2015 13:16:43 +0000 This paper presents a novel ultrawideband (UWB) bandpass filter using stepped impedance stub loaded microstrip resonator (SISLMR). The proposed resonator is so formed to allow its four resonant frequencies in the UWB passband, which extends from 3.1 GHz to 10.6 GHz. Moreover, two spurline sections are employed to create a sharp notched-band filter for suppressing the signals of 5 GHz WLAN devices. Experimental results of the fabricated filters are in good agreement with the HFSS simulations and validate the design. Ramkumar Uikey, Ramanand Sagar Sangam, Kakumanu Prasadu, and Rakhesh Singh Kshetrimayum Copyright © 2015 Ramkumar Uikey et al. All rights reserved. Implementation of a Cross-Spectrum FFT Analyzer for a Phase-Noise Test System in a Low-Cost FPGA Thu, 17 Sep 2015 07:24:08 +0000 The cross-correlation method allows phase-noise measurements of high-quality devices with very low noise levels, using reference sources with higher noise levels than the device under test. To implement this method, a phase-noise analyzer needs to compute the cross-spectral density, that is, the Fourier transform of the cross-correlation, of two time series over a wide frequency range, from fractions of Hz to tens of MHz. Furthermore, the analyzer requires a high dynamic range to accommodate the phase noise of high-quality oscillators that may fall off by more than 100 dB from close-in noise to the noise floor at large frequency offsets. This paper describes the efficient implementation of a cross-spectrum analyzer in a low-cost FPGA, as part of a modern phase-noise analyzer with very fast measurement time. Patrick Fleischmann, Heinz Mathis, Jakub Kucera, and Stefan Dahinden Copyright © 2015 Patrick Fleischmann et al. All rights reserved. Negative Group Delay Circuit Based on Microwave Recursive Filters Wed, 26 Aug 2015 11:38:52 +0000 This work presents a novel approach to design a maximally flat negative group delay (NGD) circuit based on microwave recursive filters. The proposed NGD circuit is realized by cascading stages of quarter-wavelength stepped-impedance transformer. It is shown that the given circuit can be designed to have any prescribed group delay by changing the characteristic impedance of the quarter-wave transformers (QWTs) cascaded with each other. The proposed approach provides a systematic method to synthesize NGD of arbitrary amount without including any discrete lumped component. For various prescribed NGD, the characteristic impedance of QWT has been tabulated for two and three stages of the circuit. The widths and lengths of microstrip transmission lines can be obtained from characteristic impedance and the frequency of operation of the transmission line. The results are verified in both simulation and measurement, showing a good agreement. Mohammad Ashraf Ali and Chung-Tse Michael Wu Copyright © 2015 Mohammad Ashraf Ali and Chung-Tse Michael Wu. All rights reserved. Design of Miniaturized Multiband Filters Using Zero Order Resonators for WLAN Applications Mon, 09 Mar 2015 07:42:35 +0000 The objective of this paper is to design miniaturized narrow- and dual-band filters for WLAN application using zero order resonators by the method of least squares. The miniaturization of the narrow-band filter is up to 70% and that of the dual-band filter is up to 64% compared to the available models in the literature. Two prototype models of the narrow-band and dual-band filters are fabricated and measured, which verify the proposed structure for the filter and its design by the presented method, using an equivalent circuit model. Maryam Shafiee, Mohammad Amin Chaychi Zadeh, and Homayoon Oraizi Copyright © 2015 Maryam Shafiee et al. All rights reserved. The Spiral Coaxial Cable Thu, 26 Feb 2015 12:45:30 +0000 A new concept of metal spiral coaxial cable is introduced. The solution to Maxwell’s equations for the fundamental propagating TEM eigenmode, using a generalization of the Schwarz-Christoffel conformal mapping of the spiral transverse section, is provided together with the analysis of the impedances and the Poynting vector of the line. The new cable may find application as a medium for telecommunication and networking or in the sector of the Microwave Photonics. A spiral plasmonic coaxial cable could be used to propagate subwavelength surface plasmon polaritons at optical frequencies. Furthermore, according to the present model, the myelinated nerves can be considered natural examples of spiral coaxial cables. This study suggests that a malformation of the Peters angle, which determines the power of the neural signal in the TEM mode, causes higher/lower power to be transmitted in the neural networks with respect to the natural level. The formulas of the myelin sheaths thickness, the diameter of the axon, and the spiral factor of the lipid bilayers, which are mathematically related to the impedances of the spiral coaxial line, can make it easier to analyze the neural line impedance mismatches and the signal disconnections typical of the neurodegenerative diseases. I. M. Fabbri Copyright © 2015 I. M. Fabbri. All rights reserved. An Effective Math Model for Eliminating Interior Resonance Problems of EM Scattering Sat, 31 Jan 2015 09:56:53 +0000 It is well-known that if an -field integral equation or an -field integral equation is applied alone in analysis of EM scattering from a conducting body, the solution to the equation will be either nonunique or unstable at the vicinity of a certain interior frequency. An effective math model is presented here, providing an easy way to deal with this situation. At the interior resonant frequencies, the surface current density is divided into two parts: an induced surface current caused by the incident field and a resonance surface current associated with the interior resonance mode. In this paper, the presented model, based on electric field integral equation and orthogonal modal theory, is used here to filter out resonant mode; therefore, unique and stable solution will be obtained. The proposed method possesses the merits of clarity in concept and simplicity in computation. A good agreement is achieved between the calculated results and those obtained by other methods in both 2D and 3D EM scattering. Zhang Yun-feng, Zhou Zhong-shan, Su Zhi-guo, Wang Rong-zhu, and Chen Ze-huang Copyright © 2015 Zhang Yun-feng et al. All rights reserved. Quad-Band Bowtie Antenna Design for Wireless Communication System Using an Accurate Equivalent Circuit Model Thu, 22 Jan 2015 13:25:48 +0000 A novel configuration of quad-band bowtie antenna suitable for wireless application is proposed based on accurate equivalent circuit model. The simple configuration and low profile nature of the proposed antenna lead to easy multifrequency operation. The proposed antenna is designed to satisfy specific bandwidth specifications for current communication systems including the Bluetooth (frequency range 2.4–2.485 GHz) and bands of the Unlicensed National Information Infrastructure (U-NII) low band (frequency range 5.15–5.35 GHz) and U-NII mid band (frequency range 5.47–5.725 GHz) and used for mobile WiMAX (frequency range 3.3–3.6 GHz). To validate the proposed equivalent circuit model, the simulation results are compared with those obtained by the moments method of Momentum software, the finite integration technique of CST Microwave studio, and the finite element method of HFSS software. An excellent agreement is achieved for all the designed antennas. The analysis of the simulated results confirms the successful design of quad-band bowtie antenna. Mohammed Moulay, Mehadji Abri, and Hadjira Abri Badaoui Copyright © 2015 Mohammed Moulay et al. All rights reserved. Ultrawideband Noise Radar Imaging of Impenetrable Cylindrical Objects Using Diffraction Tomography Wed, 24 Dec 2014 10:25:13 +0000 Ultrawideband (UWB) waveforms achieve excellent spatial resolution for better characterization of targets in tomographic imaging applications compared to narrowband waveforms. In this paper, two-dimensional tomographic images of multiple scattering objects are successfully obtained using the diffraction tomography approach by transmitting multiple independent and identically distributed (iid) UWB random noise waveforms. The feasibility of using a random noise waveform for tomography is investigated by formulating a white Gaussian noise (WGN) model using spectral estimation. The analytical formulation of object image formation using random noise waveforms is established based on the backward scattering, and several numerical diffraction tomography simulations are performed in the spatial frequency domain to validate the analytical results by reconstructing the tomographic images of scattering objects. The final image of the object based on multiple transmitted noise waveforms is reconstructed by averaging individually formed images which compares very well with the image created using the traditional Gaussian pulse. Pixel difference-based measure is used to analyze and estimate the image quality of the final reconstructed tomographic image under various signal-to-noise ratio (SNR) conditions. Also, preliminary experiment setup and measurement results are presented to assess the validation of simulation results. Hee Jung Shin, Ram M. Narayanan, and Muralidhar Rangaswamy Copyright © 2014 Hee Jung Shin et al. All rights reserved. A New Method of Designing Circularly Symmetric Shaped Dual Reflector Antennas Using Distorted Conics Wed, 17 Dec 2014 00:10:14 +0000 A new method of designing circularly symmetric shaped dual reflector antennas using distorted conics is presented. The surface of the shaped subreflector is expressed using a new set of equations employing differential geometry. The proposed equations require only a small number of parameters to accurately describe practical shaped subreflector surfaces. A geometrical optics (GO) based method is used to synthesize the shaped main reflector surface corresponding to the shaped subreflector. Using the proposed method, a shaped Cassegrain dual reflector system is designed. The field scattered from the subreflector is calculated using uniform geometrical theory of diffraction (UTD). Finally, a numerical example is provided showing how a shaped subreflector produces more uniform illumination over the main reflector aperture compared to an unshaped subreflector. Mohammad Asif Zaman and Md. Abdul Matin Copyright © 2014 Mohammad Asif Zaman and Md. Abdul Matin. All rights reserved. Multifrequency Oscillator-Type Active Printed Antenna Using Chaotic Colpitts Oscillator Sun, 30 Nov 2014 07:15:46 +0000 This paper presents a new concept to realize a multifrequency Oscillator-type active printed monopole antenna. The concept of period doubling route to chaos is exploited to generate the multiple frequencies. The chaotic Colpitts oscillator is integrated with the printed monopole antenna (PMA) on the same side of the substrate to realize an Oscillator-type active antenna where the PMA acts as a load and radiator to the chaotic oscillator. By changing the bias voltage of the oscillator, the antenna can be made to operate at single or multiple frequencies. To test the characteristics of the antenna at single and multiple frequencies of operation, two similar prototype models of printed monopole broadband antennas are developed. One of these antennas used at transmit side is fed by the chaotic Colpitts oscillator while the other is used as the receive antenna. It is observed that the antenna receives single or multiple frequencies simultaneously for particular values of the bias voltage of the oscillator at the transmit end. Bibha Kumari and Nisha Gupta Copyright © 2014 Bibha Kumari and Nisha Gupta. All rights reserved. Design and Investigation of Disk Patch Antenna with Quad C-Slots for Multiband Operations Wed, 19 Nov 2014 07:10:50 +0000 An investigation into the design and fabrication of multiband disk patch antenna with symmetrically quad C-slots is presented in this paper. The proposed antenna shows multiband resonance frequencies which highly depend on substrate thickness, dielectric constant, and radius of the disk patch. By incorporating two pairs of C-slots in optimum geometry on the radiating patch, the proposed antenna operates between 2 and 12 GHz at different frequency bands centered at 2.27, 7.505, 9.34, 10.33, and 11.61 GHz. The other antenna parameters are studied like gain, antenna efficiency, and radiation pattern. The proposed antenna may find applications in S-, C-, and X-band. The results are carried out with the aid of HFSS and MOM-based IE3D simulator. The measured and simulated results are in good agreement with each other. J. A. Ansari, Sapna Verma, and Ashish Singh Copyright © 2014 J. A. Ansari et al. All rights reserved. Lossy-Transmission-Line Analysis of Frequency Reconfigurable Rectangular-Ring Microstrip Antenna Thu, 13 Nov 2014 11:49:20 +0000 An analytical model for a frequency reconfigurable rectangular-ring microstrip antenna is proposed. The resonant frequencies and input impedance of the reconfigurable antenna are analyzed using a lossy-transmission-line (LTL) model. By making use of -admittance matrices, a formulation for the input impedance is analytically derived. The structure of the frequency reconfigurable antenna consists of a rectangular-ring shaped microstrip antenna which is loaded with a rectangular patch in the middle of the rectangular-ring antenna and fed by a microstrip line. RF switches are applied to connect the load to the antenna in order to reconfigure the operating frequencies. By modeling the antenna into a multiport equivalent circuit, the total input impedance is analytically derived to predict the resonant frequencies. To verify the analysis, the model input impedance and reflection coefficient calculation have been compared with the full-wave simulation and measurement results. The proposed model shows good agreement with full-wave simulated and measured results in the range of 1–3 GHz. Bambang Setia Nugroho, Fitri Yuli Zulkifli, and Eko Tjipto Rahardjo Copyright © 2014 Bambang Setia Nugroho et al. All rights reserved. Selection of Microstrip Patch Antenna Substrate for WLAN Application Using Multiple Attribute Decision Making Approach Wed, 22 Oct 2014 09:10:42 +0000 This paper presents a material selection approach for selecting microstrip patch antenna substrate for WLAN applications using multiple attribute decision making (MADM) approach. In this paper, different microwave dielectric materials for substrate and their properties like relative permittivity, quality factor, and temperature coefficient of the resonant frequency are taken into consideration and MADM approach is applied to select the best material for microstrip patch antenna. It is observed that Pb0.6Ca0.4ZrO3 is the best material for the antenna substrate in MPA for WLAN applications. It was observed that the proposed result is in accordance with the experimental finding thus justifying the validity of the proposed study. Navneet Gupta and Rituraj Raman Copyright © 2014 Navneet Gupta and Rituraj Raman. All rights reserved. Low Actuation Voltage RF MEMS Switch Using Varying Section Composite Fixed-Fixed Beam Mon, 20 Oct 2014 09:06:09 +0000 The present authors have earlier reported the employment of varying section fixed-fixed beam for achieving lower pull-in voltage with marginal fall in restoring force. Reducing Young’s modulus also reduces the pull-in voltage but with lesser degree of reduction in restoring force. Composite beams are ideal alternatives to achieve decreased Young’s modulus. Hence new varying section composite fixed-fixed beam type RF MEMS switch has been proposed. The main advantage of this RF MEMS switch is that lower pull-in voltages can be achieved with marginal fall in stiction immunity. Spring constant of the proposed switch has been obtained using simulation studies and it has been shown that the spring constant and therefore the pull-in voltage () can be considerably reduced with the proposed switch. Simulation studies conducted on the proposed switch clearly demonstrate that the pull-in voltage can be reduced by 31.17% when compared to the varying section monolayer polysilicon fixed-fixed beam. Further this approach enables the designer to have more freedom to design lower pull-in voltage switches with improved stiction immunity. M. Manivannan, R. Joseph Daniel, and K. Sumangala Copyright © 2014 M. Manivannan et al. All rights reserved. Novel Design of Microstrip Antenna with Improved Bandwidth Thu, 02 Oct 2014 12:01:43 +0000 A novel design of broadband patch antenna is presented in this paper. The broadband property of the proposed antenna is achieved by choosing a proper selection of dimensions and positions of slot and notch on the radiating patch. The bandwidth of the proposed antenna is found to be 30.5% with operating frequency band from 1.56 GHz to 2.12 GHz. Antenna characteristics are observed for different inclination angles “α” and its effect on bandwidths is also reported. The maximum gain of the antenna is found to be 9.86 dBi and it achieves broadside radiation pattern in the direction of maximum radiation over the operating band. The proposed antenna structure is simulated, fabricated, and tested for obtaining the desired performance. The simulated results are verified with experimental results which are in good agreement. Km. Kamakshi, Ashish Singh, Mohammad Aneesh, and J. A. Ansari Copyright © 2014 Km. Kamakshi et al. All rights reserved. Development of a Novel Switched-Mode 2.45 GHz Microwave Multiapplicator Ablation System Tue, 23 Sep 2014 00:00:00 +0000 The development of a novel switched-mode 2.45 GHz microwave (MW) multiapplicator system intended for laparoscopic and open surgical thermoablative treatments is presented. The system differs from the other synchronous and asynchronous commercially available equipments because it employs a fast sequential switching (FSS) technique for feeding an array of up to four high efficiency MW applicators. FSS technology, if properly engineered, allows improving system compactness, modularity, overall efficiency, and operational flexibility. Full-wave electromagnetic (EM) and thermal (TH) simulations have been made to confirm the expected performances of the FSS technology. Here we provide an overview of technical details and early ex-vivo experiments carried out with a full functional β-prototype of the system. Guido Biffi Gentili, Cosimo Ignesti, and Vasco Tesi Copyright © 2014 Guido Biffi Gentili et al. All rights reserved. A Novel Wideband Miniaturized-Element Frequency Selective Surface Sun, 21 Sep 2014 10:50:00 +0000 This letter presents a novel wideband miniaturized-element frequency selective surface (MEFSS). The simulation and measurement results show that the bandwidth of the proposed MEFSS is remarkably enhanced compared to that of an original second-order MEFSS while its size and total thickness are still small. A parametric study is also conducted to understand the operating mechanism of the proposed structure. The phenomenon observed in the parametric study is explained with an equivalent circuit model. Semyoung Oh, Hanjun Lee, Joo-Ho Jung, and Gil-Young Lee Copyright © 2014 Semyoung Oh et al. All rights reserved. High Power Combline Filter for Deep Space Applications Sun, 14 Sep 2014 08:54:33 +0000 An S-band, compact, high power filter, for use in the Mars Orbiter Mission (MOM) of Indian Space Research Organization (ISRO), has been designed and tested for multipaction. The telemetry, tracking, and commanding (TT&C) transponder of MOM is required to handle continuous RF power of 200 W in the telemetry path besides simultaneously maintaining an isolation of greater than 145 dBc to its sensitive telecommand path. This is accomplished with the help of a complex diplexer, requiring high power, high rejection transmit path filter, and a low power receive path filter. To reduce the complexity in the multipaction-free design and testing, the transmit path filter of the diplexer is split into a low rejection filter integral to the diplexer and an external high rejection filter. This paper highlights the design and space qualification phases of this high rejection filter. Multipaction test results with 6 dB margin are also presented. Major concerns of this filter design are isolation, insertion loss, and multipaction. Mission performance of the on-board filter is normal. A. V. G. Subramanyam, D. Siva Reddy, V. K. Hariharan, V. V. Srinivasan, and Ajay Chakrabarty Copyright © 2014 A. V. G. Subramanyam et al. All rights reserved. Prediction of Rain Attenuation and Impact of Rain in Wave Propagation at Microwave Frequency for Tropical Region (Uttarakhand, India) Wed, 11 Jun 2014 09:33:08 +0000 The most classical approach of determining rain attenuation for radio-wave frequency has been to theoretically determine the specific attenuation. At frequency over 10 GHz, rain and precipitation can influence the attenuation a lot; the effect of atmospheric attenuation between the source and destination over wireless communication is of major concern and a proper site visit and proper method are required to control the attenuation level so that the performance can be increased. In this paper exponential model has been used to determine the attenuation level for k-region (India) which can be used for region having similar condition. The analyzed predicted attenuation data have been compared with ITU-R measured rain attenuation, and the results will provide useful estimation of rainfall attenuation on microwave links in tropical regions that have similar conditions as (Almora) Uttarakhand region. Mukesh Chandra Kestwal, Sumit Joshi, and Lalit Singh Garia Copyright © 2014 Mukesh Chandra Kestwal et al. All rights reserved. Ultrawide Bandwidth -Hybrid-Coupler in Planar Technology Mon, 02 Jun 2014 11:38:46 +0000 A new concept of an ultrawide bandwidth 180°-hybrid-coupler is presented. The ultrawideband design approach is based on the excitation of a coplanar waveguide (CPW) mode and a coupled slot line (CSL) mode in the same double slotted planar waveguide. The coupler is suitable for realization in planar printed circuit board technology. For verification of the new concept a prototype was designed for the frequency range from 3 GHz to 11 GHz, built, and measured. The measurement results presented in this paper show a good agreement between simulation and measurement and demonstrate the very broadband performance of the new device. The demonstrated coupler with a size of 40 mm × 55 mm exhibits a fractional bandwidth of 114% centered at 7 GHz with a maximum amplitude imbalance of 0.8 dB and a maximum phase imbalance of 5°. Steffen Scherr, Serdal Ayhan, Grzegorz Adamiuk, Philipp Pahl, and Thomas Zwick Copyright © 2014 Steffen Scherr et al. All rights reserved. A Simple Method to Stabilize Radiation Pattern over a Large Bandwidth Wed, 14 May 2014 09:43:15 +0000 An alternative radiation stabilization method has been presented for patch antenna. With this method, side radiation could be suppressed when a conductor ring and a circular slot both with the width of a quarter-wavelength are placed on the same layer and around patch antenna. An experimental structure has been simulated and the distance from antenna part to conductor ring is optimized using parametric function of HFSS software. Measured results given in this paper obviously indicate that not only the side radiation from the boundary of substrate could be suppressed effectively, but also the antenna directivity could be adjusted and enhanced after this method has been carried out. Both simulation and measurement indicate that when the distance is set to one guided wavelength (), side radiation could be suppressed the most effectively and the return loss of patch antenna is only slightly affected. Haiyang Zhang, Yann Mahe, Tchanguiz Razban, and Serge Toutain Copyright © 2014 Haiyang Zhang et al. All rights reserved. Application of Response Surface Methodology to Enhance Phenol Removal from Refinery Wastewater by Microwave Process Mon, 28 Apr 2014 09:57:01 +0000 Phenol contaminated petroleum refinery wastewater presents a great threat on water resources safety. This study investigates the effect of microwave irradiation on removal of different concentrations of phenol in an attempt for petroleum refinery wastewater treatment. The obtained results show that the MW output power and irradiation time have a significant positive effect on the removal efficiency of phenol. The kinetic reaction is significantly affected by initial MW output power and initial phenol concentrations. Response surface methodology (RSM) was employed to optimize and study the interaction effects of process parameters: MW output power, irradiation time, salinity, pH, and H2O2 concentration using central composite design (CCD). From the CCD design matrix, a quadratic model was considered as an ultimate model (2 = 0.75) and its adequacy was justified through analysis of variance (ANOVA). The overall reaction rates were significantly enhanced in the combined MW/H2O2 system as proved by RSM. The optimum values for the design parameters of the MW/H2O2 process were evaluated giving predicted phenol removal percentage of 72.90% through RSM by differential approximation and were confirmed by experimental phenol removal of 75.70% in a batch experiment at optimum conditions of 439 W MW power, irradiation time of 24.22 min, salinity of 574 mg/L, pH 5.10, and initial H2O2 concentration of 10% (v/v). Sherif A. Younis, Waleed I. El-Azab, Nour Sh. El-Gendy, Shuokr Qarani Aziz, Yasser M. Moustafa, Hamidi Abdul Aziz, and Salem S. Abu Amr Copyright © 2014 Sherif A. Younis et al. All rights reserved. A Multifrequency Radar System for Detecting Humans and Characterizing Human Activities for Short-Range Through-Wall and Long-Range Foliage Penetration Applications Wed, 16 Apr 2014 17:25:41 +0000 A multifrequency radar system for detecting humans and classifying their activities at short and long ranges is described. The short-range radar system operates within the S-Band frequency range for through-wall applications at distances of up to 3 m. It utilizes two separate waveforms which are selected via switching: a wide-band noise waveform or a continuous single tone. The long-range radar system operating in the W-Band millimeter-wave frequency range performs at distances of up to about 100 m in free space and up to about 30 m through light foliage. It employs a composite multimodal signal consisting of two waveforms, a wide-band noise waveform and an embedded single tone, which are summed and transmitted simultaneously. Matched filtering of the received and transmitted noise signals is performed to detect targets with high-range resolution, whereas the received single tone signal is used for the Doppler analysis. Doppler measurements are used to distinguish between different human movements and gestures using the characteristic micro-Doppler signals. Our measurements establish the ability of this system to detect and range humans and distinguish between different human movements at different ranges. Ram M. Narayanan, Sonny Smith, and Kyle A. Gallagher Copyright © 2014 Ram M. Narayanan et al. All rights reserved. Wideband Microstrip 90° Hybrid Coupler Using High Pass Network Mon, 07 Apr 2014 13:20:18 +0000 A wideband 90° hybrid coupler has been presented and implemented in planar microstrip circuit. With similar structure of conversional 2-section branch-line coupler, the proposed coupler consists of a lumped high-pass network but not the quarter wavelength transmission at the center. The values of all lumped elements were optimized to replace a quarter-wavelength transmission line with a phase inverter. To demonstrate the proposed concept, a 1-GHz prototype was fabricated and tested. It achieves 90% impedance bandwidth with magnitude of S11 less than −10 dB. Within this bandwidth, more than 13 dB port-to-port isolation, less than 5.0 degree phase imbalance, and less than 4.5 dB magnitude imbalance are achieved, simultaneously. The proposed coupler not only achieves much wider bandwidth but also occupies less circuit area than that of the conversional 2-section branch-line coupler. Leung Chiu Copyright © 2014 Leung Chiu. All rights reserved.