A novel design of fractal dipole antenna has been presented for RFID (Radio Frequency Identification) tag applications, which is based on the fractal theory. The antenna consists of two third iteration triangle fractal arms, and has been designed to work at 900 MHz (GSM) and 2.4 GHz (ISM), and its size is 89 mm×29 mm×1.6 mm. The simulated results for various characteristics of the antenna have been shown using finite element technique based commercial software ANSOFT HFSS. The simulated and measured impedance results are in good agreement.

In this contribution, a design approach for the realization of broadband Doherty Power Amplifiers (DPAs) is proposed and demonstrated. The methodology is based on the exploitation of the wideband response of 2-sections branch-line couplers both as input splitter and output combiner of the DPA. These couplers are designed through a CAD optimization process which is specificaly oriented to the developement of DPAs. The method is also applied to realize a GaN based hybrid prototype that shows more than 36% of fractional bandwidth around 2 GHz frequency range, validated through single carriers and modulated signals (3gpp and WiMax). In single carrier mode an efficiency higher than 41% (>50% in saturation, with a peak of 72%) is obtained in 6 dB of output power dynamic range in the entire operating band. Experimental sesults with 5 MHz 3 gpp and WiMax signals shown an average efficiency of 50% and 45% when 37 dBm and 34 dBm of average output power are reached, respectively.

The fabrication of single square patch antenna for proposed Leucaena Leucocephala (``Petai Belalang'') Wood Plastic Composite (WPC) substrate board (PB Substrate board) and FR4 substrate board is presented in this paper. The experiment objective is to measure the performance of an antenna fabricated on the FR4 and PB substrate (proposed substrate) by comparing the performance in terms of material's dielectric constant and electron mobility and antennas' loss tangent, return loss (S₁₁), radiation pattern and practical antenna transmitting performance. The new substrate compositions of Leucaena Leucocephala stem and polypropylene (PP) are 30% and 70% consecutively. The result for 150 μm (sample B) indicates stability on most dielectric constant (ε_r =3.02), loss tangent (Tanδ=0.029) and electron mobility (5.31x10³ cm²/Vs), with the consistency of antenna result, between simulation and measurement. All results obtained will be analyzed and displayed in the form of data and graphs.

Ultra wideband (UWB) antenna operation close to tissue is examined by using lumped-element equivalent circuits in the present paper. The impact of tissue within the reactive near-field of the antenna is introduced in terms of efficiency, impedance and matching to 50 Ω. The parasitic components for the series- and parallel-resonant stages of the equivalent models are proposed for taking the impact of tissue into account on the antenna design. The first time the antenna impedance behaviour is presentedin terms of capacitance, inductance and resistance as a function of the radiator distance on the tissue surface for UWB antennas. The capacitance was observed to increase with the distance on the tissue surface by achieving the maximum value close to the reactive near-field boundary. The inductance has the maximum on contact the tissue, decreasing strongly with the first millimetres and remaining constant with the higher distance. The maximum value of input resistance was seen to clearly increase with the distance, having the maximum value in the first third of the studied range, descending close to the value in free space at the boundary at the end. The results are achieved by realising electromagnetic simulations for the antennas and comparing the performance with the operation of the equivalent models.

An EIT (electromagnetically induced transparency)-based prism coupler is suggested for realizing tunable reflection spectrum via quantum coherence of phases in a multilevel system, where destructive and constructive quantum interference will occur among multilevel transition pathways that are driven by two external control fields. In this prism coupler, a semiconductor-quantum-dot (SQD) medium layer, which can exhibit EIT and relevant quantum coherent effects, bounds the prism base, and the two external control fields are used to manipulate the probe field and the excited surface plasmon wave (on the SQD layer surface). Then the surface plasmon wave modes, which are generated by the probe field incident into this multilevel SQD medium layer, can be coherently tunable through the switchable quantum interference (destructive and constructive quantum interference) among the energy levels in the SQD systems. Such switchable quantum interference can be realized if we tune the intensities (i.e., adjust a proper intensity ratio) of the two control fields that drive the SQD multilevel EIT system. New switchable photonic devices, which could find applications in photonic microcircuits as well as some areas in integrated optical circuits, could be designed based on this quantum interference switchable surface plasmon resonance.

Operating frequencies for passive remote sensing have been extended to millimeter and sub-millimeter wave regions in recent years. Due to relatively shorter wavelengths, narrower beam widths can be achieved under antenna size limitations. In turn, better spatial resolution can be achieved, which is especially important for sensors in geostationary orbit. There are several mission proposals for millimeter and sub-millimeter wave payloads in geostationary orbit, e.g., Geostationary Observatory for Microwave Atmospheric Sounding (GOMAS) proposed by European countries, Geosynchronous Microwave (GEM) Sounder/Imager Observation System proposed by USA, the next generation Chinese geostationary orbit meteorological satellite FY-4, etc. The feasibility study of geostationary microwave payloads and simulation of millimeter and sub-millimeter wave atmospheric sounding data is currently underway. Many measures evaluate the efficacy of atmospheric sounding data, one of which is the Degrees of Freedom for Signal (DFS). It is independent of specific regression algorithm thus able to offer an objective measure for performance comparison and channel parameter optimization. In this paper, the DFS of a set of millimeter wave (50~70 GHz, 118 GHz, 183 GHz) and sub-millimeter wave (380 GHz, 425 GHz) sounding channels is analyzed. The DFS improvement with increasing bandwidth is given; results suggest that broader channel bandwidth will improve the efficacy and retrieval performance of the future geostationary orbit millimeter and sub-millimeter wave radiometers.

A novel prism phase modulator (PPM) for phase difference modulation between pand s-polarization lights in a surface plasmon resonance phase-sensitive imaging sensor is proposed in this paper. The PPM consists of a rhombic prism (to obtain a curve of phase difference between the two polarizations), a rotation stage and a mirror. The PPM shows great modulation stability and helps to achieve a high detection resolution. Surface plasmon resonance phase imaging is realized with a microfluidic device and a CCD camera. Experimental result shows that the detection resolution of our SPR-PI sensor based on phase-interrogation method is 7.61×10^-7 RIU with hydrous samples, which is 16 times improved compared with that based on intensity-interrogation. Real-time monitoring of the interaction between Angiogenin and anti-Angiogenin is also illustrated.

A novel CPW-fed antenna capable of triple-band operation for WLAN/WiMAX applications is presented and investigated in this paper. The proposed antenna simply consists of three elements viz. folded open stub, L-shaped open stub, and Y-shaped resonator. By using the three elements, triple-band antenna operating at 2.5/3.5/5.5 GHz can be achieved. The antenna impedance bandwidths for |S₁₁| ≤ -10 dB are 2.39-2.69, 3.38-3.73 and 5.0-5.99 GHz, covering all the WLAN/WiMAX operation bands. The tri-band antenna has good omnidirectional radiation patterns in H-plane and moderate gains across all the operation bands with compact size of 30 × 18 mm². Experimental results show that the antenna is successfully simulated and measured, and the tri-band antenna can be achieved by adjusting the lengths of the three elements and gives good gains across all the operation bands.

In this paper, we propose an analytical method for modeling a permanent magnets axial field magnetic coupling. The three-dimensional model takes into account the radial fringing effects of the coupler. The analytical solution requires resolving the Laplace equation in low permeability subdomains. The magnetic field calculation allows the determination of global quantities like axial force and torque. 3D finite element computations as well as measurements validate the proposed model.

Microwave model for simulation of radiation from the multilayer system ``sea surface - sea ice - snow cover - atmosphere'' is introduced. In the general case, ice and snow cover is modelled by multilayer medium, where every layer is characterized by its specific physical parameters. Electrodynamical properties of each layer are determined from the original authors' model of the effective permittivity of heterogeneous medium. This model takes into account effects of radiation scattering on irregularities of environment. Measurable physical characteristics of sea ice and snow are used as the model input data. This advantage allows using this model for interpretation of remote sensing images of the ice cover in the Polar Regions. Major attention is drawn to comparison of model calculations with satellite data and visual observations from ships. The collection of SSM/I and SSMIS images from GLOBAL-RT data base, and processed visual observations from ships in Arctic cruises were used. Observations data served as the input parameters for electrodynamical model. Comparison of model results with SSM/I images demonstrated good coincidence at various frequencies.

In this paper, we present five different approaches to estimate direction of arrival (DOA) of multiple incident RF sources. The proposed methods are based on extracting the signal and noise subspaces from the Q matrix, R matrix, or both Q and R matrices of the QR decomposed received data matrix. The angle of the signal arrival is extracted from the signal subspace by using similar techniques as employed by MUSIC and ESPRIT methods. The simulation results are shown which verify accurate DOA estimates for both single and two sources. In addition, an experimental verification of the proposed methods is also presented. The methods are implemented in LabVIEW software and a prototype is built using National Instruments (NI) hardware. Furthermore, the details of experimental procedures are presented which includes interfacing the uniform linear array (ULA) of antennas with the NI-PXI platform, phase difference calibration between the RF receivers, and selection of transmitter and receiver parameters. The experimental results are shown for a single and two RF sources lying at arbitrary angles from the array reference, which verify the successful real-time implement-ability of the proposed DOA estimation methods.

A novel ultra-wideband four-way in-phase multilayer power divider based on the microstrip-to-slotline transition is proposed in this paper as a complemental slotline power divider with high isolation. Due to the introduction of three lumped isolation resistors, the isolations between output ports in the new structure have been improved. The design expressions have been derived by making use of odd-mode and even-mode method. Both simulated and measured results have proved that the proposed power divider has good impedance matching at all ports, high isolations between output ports, excellent amplitude and phase balance, as well as flat group delay over the wide frequency range from 3.8 GHz to 11 GHz.

This paper presents a design approach for dual-band Wilkinson power dividers. Two pairs of parallel coupled-lines are used to replace the quarter-wavelength transformers in the conventional Wilkinson power divider to obtain dual-band operation. Using even- and odd-mode analysis, the closed-form design equations are derived for design parameters and design procedures of the proposed dual-band power divider are given. For verification purpose, a practical power divider, which operates at 1 GHz and 2.1 GHz with 3 dB power dividing ratio, is designed, fabricated and tested. The simulated and measured results are in good agreement.

Effects on the communication signals caused by the time-varying plasma sheath surrounding hypersonic vehicles are investigated. Using computational fluid dynamics (CFD) technique, Demetriades's plasma turbulence model and finite-difference time-domain (FDTD) algorithm, amplitude variation and phase fluctuation induced by plasma electron density turbulence are obtained, and their statistical properties are analyzed and characterized. Furthermore, a finite-state Markov channel (FSMC) model is proposed, to represent the dynamical effects on electromagnetic wave propagation through plasma sheath. With high accuracy and greatly reduced complexity, the FMSC model could be very useful to develop novel communication techniques for alleviating the radio blackout problem.

While Archimedean spiral antennas were invented a half-century ago, only self-complementary impedance can be evaluated directly from the Babinet's principle. This paper examines the effects of metal width and arm spacing on printed spiral's input impedance. A model is proposed based on examination by decomposition of planar spiral. A closed-form expression for the input impedance of Archimedean spiral antenna is obtained by evaluating the proposed model with conformal mapping techniques. Full-wave numerical simulations, Babinet's principle, and a fabricated antenna demonstrate the accuracy of the proposed model. The expression in this work can be used to find the impedance of a variety of spiral complementary structures analytically. The examination and discussion on the effects of other parameters and features in addition to the spiral itself are also provided through numerical simulation.

A small patch antenna is associated with passive (reactively loaded) elements (varactors) in order to auto adjust the resonant frequency in a single-channel multi-frequency configuration appropriate for biomedical applications. As a supplementary study of the authors in the field of detection of temperature abnormalities in human tissue phantom using microwave radiometry, this paper adds a contribution to frequency readjustment when a shift occur due to the fact that the human body is a complex and stratified dielectric object. The optimization of the array is performed using a Genetic Algorithm (GA) tool as a method of choice. The adjustment in the measurement frequency is performed by altering the values of the passive elements according to the shift needed.

In this paper, we present a novel 3rd filtering power divider with high in-band isolation. The proposed device employs six quarter-wavelength resonators and six internal isolation resistors symmetrically arranged to require the power division and filtering function. Based on the circuit topology, the multiple resistors can be integrated to obtain a good isolation and port impedance matching. Compared to the conventional power divider with bandpass response, the new device is easy to realize a high-order design with a good isolation. For demonstration, a prototype operating at 1.5 GHz with more than 20 dB in-band isolation is implemented. Simulated and experimental results agree well, validating the proposed methodologies.

The performance of smart antenna greatly relies on the efficient use of direction-of-arrival (DOA) estimation techniques for both coherent and non-coherent signals. In practice, DOA estimation problems and difficulties increase when the signals in multipath propagation environments are highly correlated or coherent. Therefore, exploring an algorithm which is capable of estimating coherent signals is of great importance. To overcome this problem, a new high-resolution modified virtual singular value decomposition (MV-SVD) algorithm for DOA estimation of coherent signals is proposed. It is based on the hybrid combination of the virtual array extension, singular value decomposition (SVD), and modified MUSIC algorithms. The proposed algorithm provides many features such as: decorrelation of the coherence between the signals without reducing the rank of the covariance matrix or losing the array aperture size; high-resolution and more stability especially at low SNR values; and an increase in the maximal number of detectable signals to M-1, where M is the number of antenna elements.

An improved method of quality guided phase unwrapping (QGPU) is proposed in this work. It extracts the quality map via a median filtered phase derivative variance (MFPDV) that applies a twodimensional median filter on the phase derivative variance (PDV) map, in order to reduce the effect of noise in the background area. In addition, we employed the Indexed Interwoven Linked List (I2L2) structure to store the orderly adjoin list more efficiently and the Two Section Guided Strategy (TSGS) to reduce comparison frequency. The experiments demonstrate that the normalized L1 norm of MFPDV of a brain MR image is only 0.0827, less than that of PDV method at 0.0923. Besides, the computation time of QGPU with I2L2 technique is only 30% of that with sequence structure, and the computation time of QGPU with TSGS is only 65% of that without TSGS. In total, the proposed MFPDV upwrap phase images better than conventional PDV map, and I2L2 and TSGS are efficient strategies to reduce computation time.

We use a gradient-based material distribution approach to design conductive parts of microstrip antennas in an efficient way. The approach is based on solutions of the 3D Maxwell's equation computed by the finite-difference time-domain (FDTD) method. Given a set of incoming waves, our objective is to maximize the received energy by determining the conductivity on each Yee-edge in the design domain. The objective function gradient is computed by the adjoint-field method. A microstrip antenna is designed to operate at 1.5 GHz with 0.3 GHz bandwidth. We present two design cases. In the first case, the radiating patch and the finite ground plane are designed in two separate phases, whereas in the second case, the radiating patch and the ground plane are simultaneously designed. We use more than 58,000 design variables and the algorithm converges in less than 150 iterations. The optimized designs have impedance bandwidths of 13% and 36% for the first and second design case, respectively.