This paper presents the development of an Ultra Wide Band (UWB) monopole antenna with dual band notch characteristics. Modified crown-square shaped fractal slots in the ground-plane are implemented to enhance the impedance bandwidth to around 58% as compared to conventional square monopole antenna without slots. Impedance bandwidth of the proposed antenna is approximately 114% with Voltage standing wave ratio (VSWR)<2. In addition to this, two omega-shaped (Ω) slots have been incorporated in the radiating patch to render band-notch characteristics centered at 5.5-GHz band assigned to IEEE802.11a and HIPERLAN/2 as well as X-band for satellite communication centered at 7.5-GHz band. Measured antenna gain is stable over the entire UWB region except at the notch bands. Radiation pattern of the antenna show that the proposed antenna exhibits nearly monopole like E plane radiation patterns and omni-directional H plane radiation patterns throughout the band. A fabricated prototype is developed with close agreement between simulated and measured results.

A novel broadband absorber using the fractal tree structure is presented in this paper, which consists of three metallic layers separated by two dielectric substrates. Five metallic vias connect these three layers which make the whole structure like a two order fractal tree. Simulated and measured results show that this absorber can provide a high absorptivity level from 4.98 to 12.58 GHz, equivalent to a relative absorption bandwidth about 87%. Further investigations show that this wideband absorption can be attributed to the multi-eigenmodes and lower quality factor of the fractal tree structure.

With the vast emergence of new mobile applications, multiband operation in a compact size is mandatory for market penetration. In this paper, a new mobile handset antenna suitable for both mobile and wireless LAN services is presented. The antenna operates for most of the mobile applications such as the GSM 900, DCS 1800, PCS 1900, UMTS 2100, and most of the LTE bands, especially the low frequency LTE 700 band at -10 dB. The antenna also supports the WIMAX, WLAN, and the ISM bands. The antenna not only has a compact size, but also supports a low SAR radiation at all the operating frequencies. The antenna consists of two concentric open rings that act as quarter wavelength monopoles. The inner ring radiates at 900 MHz, while the outer ring radiates at 700 MHz. The inner ring works as a monopole radiator as well as a slot radiator fed by another rectangular monopole. The advantage of the slot is that it supports a wide range of modes that by its role open the radiation band from 1.65 to 3.6 GHz. The antenna meets three challenging parameters: compact size, multiband operation including low frequency bands, and low SAR radiation. Good agreement is noticed between the experimental and simulated results.

This paper presents an optimized design of Litz-wire coil pair with ferrite substrates based on a set of analytical expressions and a 2-D finite-element analysis (FEA) in a way that the coupling coefficient is maximized. An investigation is made on key structure parameters of coils (e.g., structure of Litz-wire, number of turns, and number of layers) to determine their influence on self-inductance and mutual inductance respectively. The influence of ferrite substrate (e.g., relative permeability and thickness) is also considered. Different types of fabricated coils are used to verify all analytical expressions and optimization methods, and it is found that the theoretical predictions and simulations are in agreement with the measured results.

Wireless communication along the stairwell in a high rise building is important to ensure immediate response to take place via consistent relaying of necessary information or data in emergency situations. Thus, a good understanding of signal wave attenuation along the stairwell is necessary to allow a better wireless network planning. This paper presents empirical path loss prediction model for multi-floor stairwell environment. The proposed model is based on measurement in 4 different stairwells, at 900 MHz and 1800 MHz which are near public safety communication bands. The model incorporates the effect of different floor heights and unique path loss-to-distance relation on several stair flights observed during measurement campaign. The proposed model demonstrates higher accuracy than 3 standard path loss models at 2 other stairwells.

This work presents an evaluation of the measurement challenges in clinical testing of our microwave breast cancer screening system. The time-domain radar system contains a multistatic 16-antenna hemi-spherical array operating in the 2-4 GHz frequency range. We investigate, for the first time with such a system in clinical trials, the repeatability of measurements and its effect on image reconstruction. We record vertical and horizontal measurement uncertainties under different scenarios and verify, using previously introduced compensation methods, that they can be successfully reduced to an acceptable level from the standpoint of image reconstruction. We also examine how placement of an immersion medium can affect collected breast scan data. Finally, we probe the repeatability and consistency of measurements with patients. With the goal of confirming the feasibility of frequent breast health monitoring, with our system, we obtain a total of 342 breast scans collected over 57 patient visits to determine how much scan data varies when there are no changes in between scans, and how much it varies when the patient is repositioned in the system. We confirm that, by taking care in patient positioning in the system and with respect to the immersion medium, the measurement repeatability is high.

Target recognition through the processing of high-resolution radar images has been an active research area in past decades. In this paper, dictionary sets parameterized by the two-dimensional (2-D) location parameters of main high-energy scatterers are considered to recognize the candidate targets. For this purpose, the scatterer extraction and orientation estimation of radar image are firstly provided in this paper. Furthermore, the recognition method based on the parameterized dictionary sets is subsequently proposed. Different from the existed recognition methods, only the sampled images at the 2-D location parameters of main high-energy scatterers are used in the proposed method. Consequently, the noise or clutter outside the sampling locations can be filtered, which results in more robust performance. Moreover, the 2-D location parameters are proportional to the geometrical structure, and the proposed method is adaptive to the scale variation of the target images. Simulated results are provided to demonstrate the proposed method.

A compact asymmetric coplanar strip fed wide-band monopole antenna with modified L-shaped ground plane for WLAN applications is presented. The proposed antenna operating at 5.5 GHz covering IEEE802.11WLAN/RFID/HYPERLAN2. The antenna has an overall dimension of only 21 x 7.35 mm² when printed on a substrate of dielectric constant 4.4. The planar design, simple feeding technique and miniaturized size make it easy for the integration of the antenna into circuit boards. Details of the antenna design and simulated and experimental results are presented and discussed.

Selective wavelength tuning of multiple quantum well based infrared photodetector is achieved by nonuniform doping distribution as well as dimensional variation in the structure. Result is obtained from the computation of the intersubband transition energy through self-consistent solution of the Poisson's and Schrödinger equations with appropriate boundary conditions. Absorption coefficient is estimated in presence of external electric field applied along the direction of confinement. Suitable choice of structural parameters is required to tailor the peak position of absorption spectra for application in the infrared range as optical receiver.

A general procedure to evaluate the electromagnetic fields generated by moving seawater through the geomagnetic field is proposed. It contains two essential steps: modeling of velocity vector of seawater according to its dynamic mechanism, and solution of Maxwell equations under a stratified ocean configuration. Two kinds of motions are considered in this work, wind-driven waves and wakes due to a moving body. The ocean is taken to be infinitely deep at the moment. Both the velocity vector and magnetic field are expressed as a superposition of sinusoidal waves. Simulation results show that the magnetic fields produced by moderate wind waves or a middle-size body moving at moderate speed are on the order of one hundred pico-Tesla near the sea level. The spectrum characteristics of the two kind magnetic anomalies are distinct.

A novel and simple dual-band dual-sense circularly polarized (CP) metal-strip antenna is proposed. The antenna fed by a coplanar waveguide (CPW) with the advantages of uniplanar geometry and easier fabrication consists of a square slot and two split-ring elements. By appropriately introducing dual split-ring elements, the proposed dual-band CP design can easily be achieved. The two resonant frequencies are controlled by the size of the two split-ring elements. The proposed antenna prototype is fabricated and measured. Experimental results show that good CP radiation performances are obtained at both resonant frequencies. The proposed antenna has an impedance bandwidth (|S₁₁|≤-10 dB) of 63.3% (2.0~3.9 GHz), and the dual band circular polarization with left hand circular polarization (LHCP) at 2.2 GHz and the right hand circular polarization (RHCP) at 3.8 GHz are obtained. Also, the 3-dB axial ratio bandwidths are about 220 and 190 MHz at the lower and upper band, respectively.

Electromagnetic wave absorption inside a human body is investigated. The human body has been modeled using 3D voxel based dataset considering different electrical parameters. At GSM 900 band, Specific Absorption Rate (SAR) induced inside the human body model exposed to a radiating base station antenna (BSA) has been calculated for multiple number of carrier frequencies and input power of 20 W/carrier. Distance (R) of human body from BSA is varied in the range of 0.5 m to 5.0 m. Values of whole-body average SAR obtained by hybrid FDTD method closely match with that obtained by SFDTD method. For number of carrier frequency equal to five and R = 0.5 m, maximum value of whole-body average SAR obtained by both hybrid FDTD and SFDTD method is found to be 0.69 W/kg which decreases either with increase of R or decrease of number of carrier frequencies. Safety distance for general public is found to be 1.5 m for number of carrier frequencies equal to five. Summary of performance comparison shows that hybrid FDTD method is faster and requires less memory than SFDTD method.

This paper is devoted to the study of beam-wave interaction behavior of a 35 GHz photonic band gap cavity (PBGC) gyrotron operating in a higher order TE₃₄₁ mode. For the present gyrotron, PBGC is used instead of conventional tapered cylindrical cavity due to its promising feature of the mode selectivity. In order to observe the beam-wave interaction behavior, multimode theory has been used for the PBG cavity operating at the fundamental harmonic mode. Multimode theory provides the performance of a gyrotron in the presence of all competing modes. Results obtained from the analysis have been validated using a commercially available 3D PIC code. The energy and phase variations of electrons demonstrate the bunching mechanism as well as energy transfer phenomena. RF power output obtained from the analysis as well as PIC simulation is compared and is found in close agreement within 12%. More than 45 kW of stable RF power output is achieved in TE₃₄₁ mode with ~17% efficiency. The existence of competing modes has been considerably reduced, and the single mode operation of PBGC gyrotron has been achieved.

Tracing the dynamics of electrons inside atoms molecules or solids as they occur in real time resides at the forefront of modern science and technology. Advances in attosecond physics over the last decade and beyond are now enabling this essential experimental capability. Here we discuss some of the key developments in light sciences that made possible attosecond metrology and control of electronic processes inside matter on native time scales. These developments hold the promise for new, fundamental insights into the innerworkings of the microcosm as well as the identification of innovative routes for light-based electronic and photonic devices operating at PHz rates.

The paper is devoted to the theory of eigen electromagnetic waves propagating across the axis of symmetry in waveguides with a non-circular cross-section. The case of waveguides filled with isotropic cold plasma is studied theoretically. Plasma particles motion is described in fluid approximation; expressions for the waves' fields are derived from Maxwell equations. Cross-section of the studied waveguide is modeled by Fourier series with coefficients, which values are less than unity. This allows one to apply method of successive approximations for analytical research of this problem. Boundary conditions, which are formulated in non-linear form over the small parameters of the problem have been applied for derivation the dispersion equations, which determine frequency spectrum of these surface waves for waveguides of different constructions. Studied eigen electromagnetic waves propagate in the form of wave packets, which are approximately described by the main azimuthal harmonic and two nearest satellite spatial harmonics. Represented results have been obtained both analytically and numerically. Possible spheres of the studied eigen waves are discussed.

An ultra-wideband (UWB) bandpass filter (BPF) with hybrid coplanar waveguide (CPW)/microstrip structure is introduced in this paper. Then a pair of lowpass filters is integrated on the CPW feed lines to achieve a good out-of-band rejection. At last, a notched band with two transmission zeros is realized at 5.8 GHz by using a symmetric E-shaped slot-line and etching slots on microstrip resonator. Two transmission zeros are realized in the desired notched band, and out-of band rejection is more than 32 dB. In order to prove the validity, the proposed filter is fabricated and measured, and the measured results are in good agreement with simulated ones.

The near-field scattering characteristics of rough target are analyzed by using a revised bidirectional reflectance distribution function (BRDF) of a rough surface based on least squares support vector machine (LS-SVM). The revised BRDF is more reliable in a larger range of incident angles and scattering angles that beyond the scope of experimental measurements. The basic principle of LS-SVM and the modeling process are firstly introduced in detail. Then the comparison among LS-SVM, the back propagation neural network (BPNN) and the measured data is carried out．The results show that the LS-SVM model has better integrative performance, stronger generalization ability and higher precision. On this basis, the calculation of the near-field radar cross section (RCS) of a complex target is safely performed and analyzed. The method proposed is helpful to better investigate the near-field scattering characteristics of rough target.

Electromagnetic imaging is based upon the fundamentals of electromagnetic (EM) fields and their relationship with the material properties under evaluation. A new system based on a Giant Magneto-Resistive (GMR) sensor array was built to capture the scattered EM signal returned by metallic objects. This paper evaluates the new system's capabilities through the classification of metallic objects based on features extracted from their response to EM fields. A novel amplitude variation feature as well as the combinations of typical features is proposed to obtain high classification rates. The selected features of metallic objects are then applied to well-known supervisedclassifiers (ANN and SVM) to detect and classify `threat' items. A collection of handguns with other commonly used metallic objects are tested. Promising results show that a high classification rate is achieved using the proposed new combination features and classification framework. This novel procedure has the potential to produce significant improvements in automatic weapon detection and classification.

Electromagnetic band gap (EBG) structures are usually realized by periodic arrangement of dielectric materials. These periodic structures can help in the reduction of mutual coupling in array antennas. In this paper a new arrangement of EBG structures is presented for reducing mutual coupling between patch antenna MIMO arrays. The patch antennas operate at 5.35 GHz which is defined for wireless application. Here 2×5 EBG structures are used to reduce mutual coupling more than 20 dB. The total size of the antenna is 36 mm×68 mm×1.6 mm. So it is more compact in than pervious research. Experimental results of return loss and antenna pattern have been presented for 5.4 GHz and compared with HFSS simulation results. Also the EBG structures have been designed with numerical modeling and dispersion diagram. New EBG model is compared with conventional EBG model, and equivalent circuit model is given for new structure.

In this paper, a compact asymmetric coplanar strip (ACS)-fed printed monopole antenna for tri-band WLAN/WiMAX applications is presented. The proposed antenna is composed of a simple monopole with the high resonant mode at 5.8 GHz, an open-ended slot embedded on the ground plane with the low resonant mode at 2.4 GHz, and a meander trip shorted to the ground with the middle resonant mode at 3.5 GHz. The three resonance frequencies of the antenna can be controlled by adjusting the geometries and the sizes of the monopole, the slot and the strip. The antenna occupies a very compact size of 22×12 mm² including the ground plane, has nearly omnidirectional radiation characteristics and reasonable gain in the operating bands. The simple feeding structure, compactness and uniplanar design make it easy to be integrated within the portable device for wireless communication.