A pattern synthesis approach based on a modified alternating projection method in an affine coordinate system is proposed in this paper. The approach is suitable for large planar arrays with periodic parallelogram element layout. According to the affine transformation theory, the radiation pattern of the array with a periodic parallelogram element layout could be written down immediately from that of a conventional one with rectangle cells when a pattern invariant group is defined. Just as known, the conventional alternating projection method is sensitive to the starting point and easy to fall into local optimum; in this paper we introduce a modified alternating projection method with a variable projection operator. To verify the rationality of the proposed method, several examples have been performed on our personal computer. Results show that the method could quickly synthesize the array patterns to the required with high accuracy. In addition, if the array has a triangle or parallelogram element layout, the required antennas to fill up the aperture is reduced when compared with the conventional one with antennas arranged along a rectangle grid. In our examples, the maximum reduction is about 18.09%, which is quite beneficial to reduce the weight and cost of the array.

One of the most important aspects for body centric communication is the development of the textile antenna for on-body communication. Antennas for on-body environment usually suffer performance degradation caused by the human body. Apart from that, textile antenna gets easily bent, flexed, wrinkled or wet. This paper presents an investigation on three different designs and types of planar antennas, which are single band textile dipole antenna, fractal Koch multiband dipole antenna and monopole ultra wide band antennas. The performance of the antennas has been evaluated in terms of bending, wetness condition and on-body simulation. The results show that the bending effect is not critical in free space for the planar antennas, but the performance is notably degraded under wet condition while the antenna reflection coefficient is shifted when placed on the human body.

A coupled-line circuit structure is proposed in this paper to design a modified Schiffman phase shifter with short reference line. Based on the traditional transmission line theory and ABCD parameters, closed-form mathematical equations for electrical and scattering parameters are obtained. Obviously, this proposed coupled-line phase shifter has several advantages such as arbitrary phase difference, easy implementation, and analytical design method. Finally, two examples of microstrip coupled-line phase shifter, which have fractional bandwidth over 45%, are fabricated and measured. Good agreements between the simulated and measured results verify our design.

A compact ultrawideband (UWB) multiple-input-multiple-output (MIMO) antenna with a small size of 22×36 mm² is proposed for portable devices. The MIMO antenna consists of two symmetric slot antenna elements with back-to-back separation of 7 mm. Adjusting the open-ended stepped radiator and position of the microstrip line can realize UWB impedance matching. In order to achieve wideband and high isolation, a cross-shaped decoupling slot and connecting metal line are etched on the ground plane. The cross-shaped slot between the antenna elements is used to decrease the mutual coupling caused by near-field at middle and high bands. The connecting line can be interpreted as a neutralized line, which produces an additional current path for the coupling ground currents. Measured S-parameters show that the isolation is better than -16 dB across the UWB of 3.1-10.6 GHz. The radiation pattern, gain, and envelope correlation coefficient are also measured. The proposed antenna with a simple structure and compact size achieves good impedance matching and excellent port isolation simultaneously, and is a good candidate for UWB MIMO systems.

A miniaturized annular ring slot antenna is presented. The antenna consists of an annular ring slot structure and a novel folded matching structure. The annular ring slot structure is printed on a substrate and shorted concentrically with a set of conductive vias. The additional matching structure is a ring cavity attached to the back of the annular ring slot structure. Firstly, the diameter of the proposed antenna is reduced by using the folded matching structure comparing with traditional annular ring slot antennas. Secondly, the impedance matching of the proposed antenna is achieved by optimizing the size of the matching structure. A prototype of the proposed antenna with a height of 3.048 mm (0.03λ) and a radius of 47.2 mm (0.4λ) is designed, fabricated and measured. The antenna resonates at 2.67 GHz and has a monopole-like radiation pattern, which shows that the antenna is suitable for the applications of taking off, landing, and long distance communications for a small or mini UAV.

In this paper, a cross-slot-coupled dual-band circularly polarized (CP) hybrid dielectric resonator antenna (DRA) is presented. The design concept is based on using a cross-slot as both a feeding structure of the DRA and an effective radiator. Full wave simulation is used to verify the proposed design concept in this paper. A prototype antenna is designed, fabricated, and measured. Good agreement is obtained between the simulated and measured results.

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.