Circularly polarized millimeter-wave travelling-wave antennas, using substrate integrated circuits (SICs) technology, are designed, fabricated and tested. By using the SICs technology, compact antennas with low losses in the feeding structure and with good design accuracy are obtained. The elementary antenna which is composed of two inclined slots is characterized by full-wave simulations. This characterization is used for the design and development of linear antenna arrays with above 16 dB gain and low side lobe level (<-25 dB), using di®erent power aperture distributions, namely uniform, Tchebychev and Taylor. Experimental results are presented at 77 GHz showing that the proposed antennas present good performances in terms of impedance matching, gain and axial ratio. These antennas have potential applications in integrated transceivers for communication and radar systems at millimeter-wave frequencies.

This paper proposes a method to estimate human exposure to electromagnetic field radiation in a variable and highly multiscale problem. The electromagnetic field is computed using a combination of two methods: a rigorous time domain and multiscale method, the DG-FDTD (Dual Grid Finite Difference Time Domain) and a fast substitution model based on the use of transfer functions. The association of these methods is applied to simulate a scenario involving an antenna placed on a vehicle and a human body model located around it. The purpose is to assess the electromagnetic field in the left eye of the human body model. It is shown that this combination permits to analyse many different positions in a fast and accurate way.

In this paper, indirect microwave holographic imaging of concealed ordnance is demonstrated. The proposed imaging technique differs from conventional microwave imaging methods in that it does not require the direct measurement of the complex field scattered from the imaged object but mathematically recovers it from intensity-only scalar microwave measurements. This brings the advantages of simplifying the hardware implementation and significantly reducing the cost of the imaging system. In order to demonstrate the ability of the proposed technique to reconstruct good quality images of concealed ordnance, indirect microwave holographic imaging of a metallic gun concealed in a pouch is carried out for airport security imaging applications. It is demonstrated that good resolution amplitude and phase images of concealed objects can be recovered when back-propagation is applied.

Previous invisibility cloaks were based on metamaterials, which are difficult for practical realization in visible light spectrum. Here we demonstrate a unidirectional invisibility cloak in visible light spectrum. By using water as the effective material and separated into several regions by glass sheets, a simplest and cheapest invisible device is realized. This device can hide macroscopic objects with large scale and is polarization insensitive. Owing to simple fabrication and easily acquisitive materials, our work can be widely applied in our daily life.

The contribution of electromagnetic wave scattering on density irregularities in the volume component of radar backscatter was analyzed for a thick snow pack containing internal hoar/ice layers. To evaluate the effect of this scattering, Density Deviation Factor (DDF), a statistical parameter, was introduced into the backscattering coefficient using the ``slice'' approach. DDF is proportional to the intensity of the density fluctuation and inverse to the mean density. The inverse dependence of backscatter with accumulation rate was discussed based on the DDF parameterization of snow inhomogeneities.

The paper presents a method of determination of ground fault current distribution when HV (high voltage) substations are located in urban or suburban areas, or where many relevant data necessary for determination of this distribution are uncertain or completely unknown. The problem appears as a consequence of the fact that many of urban metal installations are situated under the surface of the ground and cannot be visually determined or verified. On the basis of on-the-site measurements, the developed method enables compensating all deficiencies of the relevant data about metal installations involved with the fluctuating magnet field appearing around and along a feeding power line during an unbalanced fault. The presented analytical procedure is based on the fact that two measurable quantities, currents in one phase conductor and in one neutral line conductor, cumulatively involve the inductive effects of all, known and unknown surrounding metal installations. Once, this quantity has been determined, the problem of determination of different parts of a ground fault current becomes solvable by using a relatively simple calculation procedure. The presented quantitative analysis indicates at the benefits that can be obtained by taking into account the presence of surrounding metal installations.

A new ultra-wideband antenna with enhanced, nearly constant gain is presented. This quasi-planar antenna is composed of a CPW-fed printed monopole and a short horn, both made out of a single substrate. The measurements demonstrate an almost at peak gain of 5.5 dBi0.7 dB from 2.5 GHz to 15 GHz with the average gain difference in XZ plane is roughly 2 dB up to 8 GHz, which further rise to 6 dB at 10 GHz. The antenna also has a nearly linear phase response in this band. Well tested performance both in frequency and time domains, along with broad azimuth pattern, results in minimal ringing of a radiated pulse. The new antenna is suitable for establishing good line of sight link for UWB transmission and other broadband applications.

This paper presents a frequency and pattern reconfigurable stacked patch microstrip array antenna fed by aperture-coupled technique. The antenna consists of three substrate layers with radiating elements sorted at substrate layer 1 (top patches) and substrate layer 2 (bottom patches). The layers have different sizes to indicate different operating frequencies. On the ground plane, the four sets of two different aperture slot shapes (I-shaped and H-shaped) are used to transfer the wave and signal to particular radiating elements during the PIN diode switches configurations. The I-shaped slots are used to activate the bottom patches while the H-shaped slots are used to activate the top patches. Four PIN diode switches are placed at the feed line, positioned between the I- and H-shaped slots. Next, by changing the PIN diode switches configuration to ten cases, the proposed antenna has capabilities to change the operating frequencies and the pattern characteristics itself. The measured results of return loss, gain and radiation patterns are slightly shift compared to the simulated results.

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.