This paper presents a development of a wideband delta-sigma modulator for fully digital GHz transmitters. The fully digital RF transmitter is developed as a promising solution for software defined radio (SDR) terminals and applications. The fully digital transmitter consists of a delta-sigma modulator, a high-speed multiplexer and a switching-mode power amplifier. The speed limitation of delta-sigma modulator is the main limitation to increase the signal bandwidth in fully digital transmitters. In this paper, the bandwidth of the fully digital transmitter is increased 8 times using parallel processing time-interleaved architecture, while maintaining the same signal quality. This architecture was implemented on FPGA and tested for different standards (WiMAX and LTE) with a signal bandwidth up to 8 MHz. The concept was assessed in terms of SNDR by using a differential logic analyzer at the output of FPGA, and the SNDR was found to be around 60 dB.

In this paper, a new kind of printed TEM horn antenna with high-gain fed by balanced microstrip line is proposed. The radiation part of the antenna (printed on the FR4 epoxy substrate) is composed of two symmetrical triangular metal foil branches fed by balanced microstrip line. The antenna has been simulated by CST MICROWAVE STUDIO^® software, and the simulated results show that the proposed antenna is a kind of traveling wave antenna. Besides, an equivalent adopted V-shaped antenna model is proposed to describe the radiation characteristic of the antenna. The simulated and measured results indicate that in the frequency range from 1.64 GHz to 9 GHz, the reflection coefficient of the antenna is less than -6 dB, and in the work frequency band, the average gain value is over 8.2 dB. The antenna gain will be improved greatly by extending the length of the dielectric slab appropriately (in the main radiation direction) without influencing the bandwidth. The measured and simulated results have a good consistency. This antenna will have wide application in the UWB field.

The adaptive sliding-mode observer has been widely used to estimate the rotor flux and rotor speed in inverter-fed sensorless induction motor drives. However, the technique requires setting a priori the sliding-mode observer constants and also knowledge of the induction motor parameters. This particular aspect can cause significant errors in the estimation of the rotor speed used in sensorless control schemes. Changes in the induction machine parameters due to temperature or different saturation levels will affect the dynamic operation of the observer despite its adaptive nature. In this context, a sensitivity study of the adaptive sliding-mode observer is presented and discussed in this paper. Various experiments are performed on a sensorless indirect vector-controlled induction motor drive under a variety of conditions to verify the observer robustness.

In this paper, we propose the design of high sensitivity and selectivity metamaterial-based biosensors operating in the THz regime. The proposed sensors consist of planar array of resonant metallic structures, whose frequency response is modified through the variation of the surrounding dielectric environment. We consider different resonator geometries, such as the squared, circular, asymmetrical, and omega ones, and the analysis of the biosensors is conducted through proper equivalent quasi-static analytical circuit models. The metallic particles are assumed deposited on a glass substrate through proper titanium adhesion layers. Exploiting the proposed analytical model, which is verified through the comparison to full-wave numerical simulations, we study the biosensor resonance frequencies as a function of the geometric parameters of the individual inclusions. Finally, we optimize the structure in order to obtain high sensitivity and selectivity performances. The numerical results show that the proposed structures can be successfully applied as biosensors working in the THz region.

A miniaturized printed log-periodic fractal dipole antenna is proposed. Tree fractal structure is introduced in an antenna design and evolves the traditional Euclidean log-periodic dipole array into the log-periodic second-iteration tree-dipole array (LPT²DA) for the first time. Main parameters and characteristics of the proposed antenna are discussed. A fabricated proof-of-concept prototype of the proposed antenna is etched on a FR4 substrate with a relative permittivity of 4.4 and volume of 490 mm × 245 mm × 1.5 mm. The impedance bandwidth (measured VSWR < 2) of the fabricated antenna with approximate 40% reduction of traditional log-periodic dipole antenna is from 0.37 to 3.55 GHz with a ratio of about 9.59 : 1. Both numerical and experimental results show that the proposed antenna has stable directional radiation patterns and apparently miniaturized effect, which are suitable for various ultra-wideband applications.

In this paper, we consider a dense array of metallic circular patches printed on a electrically thin metal-backed dielectric substrate. Since the sub-wavelength dimensions, the array and the metal-backed substrate can be described in terms of a lumped capacitance and a lumped inductance, respectively. Around the resonant frequency, the structure, known as high-impedance surface, reflects totally an incident electromagnetic wave with zero shift in phase. Due to this property, it is widely employed in antenna systems as compact back reflector with improved performances with respect to typical metal reflector. Starting from the concept of the grid capacitive reactance of a planar array of squared patches and its related formulas, we investigate on the field distribution on the array plane and properly modify the formulas for the case of the circular patches. We present two new analytical formulas which can be effectively used for the fast design of 2D-isotropic circular HISs. In order to validate the models, we compare the resonant frequency of the array obtained through our approaches to the one resulting from full-wave numerical simulations and from other analytical methods available in the open technical literature.

Based on quasi-static electromagnetic field theory, recently grounding system under alternative currents (AC) substation has been studied with equal potential and unequal potential models. In these numerical models, the closed form of Green's function for a point source within a horizontal multilayered earth model and its quasi-static complex image method have been fully discussed. However, less information about how to achieve the closed form of Green's function through Matrix Pencil method is presented in these references. In this paper, we discuss how the kernel of the Green's function can be expanded into a finite exponential series.

A novel microstrip dual-mode tri-band bandpass filter is presented. The filter consists of an open stub loaded dual-mode resonator and two short stub loaded dual-mode resonators. By utilizing the odd- and even-mode resonance properties of the proposed dual-mode resonators and the introduced source-load coupling (S-L coupling), the filter is designed with two transmission zeros at both sides of each passband, which will improve the selectivity of the filter. To validate the design theory, one 100 MHz 3 dB absolute equal bandwidths dual-mode tri-band filter with three passbands located at the centre frequencies of 1.8, 2.4 and 5.0 GHz, respectively, is designed and fabricated. Both experimental results agree well with the simulations.

Rain attenuation is an important aspect of signal propagation above 10 GHz frequency. The attenuation time series generation from point rain rate measurement is crucial due to unavailability of actual signal measurements. In this paper, a simple and realistic approach has been demonstrated for better estimation of rain attenuation using Ku-band signal propagation data and ground rain rate measurements at Kolkata, India. The ITU-R model of rain attenuation has been modified by incorporating an effective slant path model. The effective slant path has been estimated and modelled in terms of a power-law relationship of rain rate data of 2007-2008. The methodology has been validated with the measured data of 2006. Comparison with ITU-R and SAM clearly demonstrates the improved predictability of the proposed model at the present tropical location.

Microwave Imaging is one of the most promising emerging imaging technologies for breast cancer detection, and exploits the dielectric contrast between normal and malignant breast tissue at microwave frequencies. The development of many UWB Radar imaging approaches requires the use of accurate numerical models for the propagation and scattering of microwave signals within the breast. The Finite-Difference Time-Domain (FDTD) method is the most commonly used numerical modelling technique used to model the propagation of Electromagnetic (EM) waves in biological tissue. However, it is critical that an FDTD model accurately represents the dielectric properties of the constituent tissues, including tumour tissues, and the highly correlated distribution of these tissues within the breast. This paper presents a comprehensive review of the latest findings regarding dielectric properties of normal and cancerous breast tissue, and the heterogeneity of normal breast tissue. Furthermore, existing FDTD models of the breast described in the literature are examined.

A novel dual-mode double square loop resonator (DMDSLR) for dual-band band-pass filter (BPF) is presented in this paper. The simple meander loop in DMDSLR is studied to improve the performance of the conventional DMDSLR. Significant size reductions over 33% are achieved. In addition, the designed meander-loop DMDSLR filter shows lower insertion loss (2.24 and 2.28 dB), higher rejection level (28/56 dB and 53/36 dB), wider bandwidth (about 8.5% and 28%) at the 2.47 and 5.47 GHz bands, respectively. Two transmission zeros are placed between the two pass-bands and result in a good isolation.

In this paper, the self-complementary principle has been applied to develop the traditional planar monopole antenna into a dipole antenna whose frequency range exceeds UWB requirements. The proposed design has compact, planar, and simple shape arranged in self-complementary manner connected to the (SMA) connector via rectangular microstrip line. The self-complementary structure offers better reduction of the imaginary part of antenna impedance, which allows matching on a wider band of frequencies. The proposed antenna showed -10 dB return loss bandwidth extending from 1.86 GHz up to 17.7 GHz. Moreover, this antenna has a simple shape as compared with complicated and irregular shapes with curves, slots or parasitic elements. The proposed design is validated by experimental measurements. The phase of the return loss is investigated for more insight into antenna matching.

A compact dual-band patch antenna is proposed and measured in this paper. The proposed antenna employs a U-shaped slot and two mitered corners to achieve two operating frequency bands, 2.30-2.50 GHz and 4.50-6.36 GHz, which meet the specifications of IEEE 802.11b/g/a standard for WLAN applications. Full wave analysis is performed to simulate the characteristics of the proposed antenna using CST microwave studio. Moreover, a fabricated prototype which has compact dimensions of 20.0 mm × 25 mm × 1 mm exhibits agreement between measured and simulated parameters and radiation patterns.

A dual-core photonic crystal fiber (DC-PCF) is proposed, and bending characteristics of the DC-PCF are investigated. Two fiber cores are employed in the cross-section of the DC-PCF, which result in a mode coupling between the two fiber cores when the light propagates inside the DC-PCF. The mode coupling between two fiber cores of the DC-PCF is sensitive to the directional bending of the DC-PCF which essentially provides a method to achieve bending sensing. A DC-PCF-based bending sensor is proposed by injecting a broadband light into one fiber core of the DC-PCF on one side and detecting output spectrum from another fiber core of the DC-PCF on the other side. In our simulations, a parabola curve which shows the relationship between the wavelength shift of the transmission spectrum of the DC-PCF-based bending sensor and the bending curvature of the DC-PCF is presented.

The rigorous uncertainty estimation in Electromagnetic Compatibility (EMC) testing is a complex task that has been addressed through a simplified approach that typically assumes that all the contributions are uncorrelated and symmetric, and combine them in a linear or linearized model using the error propagation law. These assumptions may affect the reliability of test results, and therefore, it is advisable to use alternative methods, such as Monte Carlo Method (MCM), for the calculation and validation of measurement uncertainty. This paper presents the results of the estimation of uncertainty for some of the most common EMC tests, such as: the measurement of radiated and conducted emissions according to CISPR 22 and radiated (IEC 61000-4-3) and conducted (IEC 61000-4-6) immunity, using both the conventional techniques of the Guide to the Expression of Uncertainty in Measurement (GUM) and the Monte Carlo Method. The results show no significant differences between the uncertainty estimated using the aforementioned methods, and it was observed that the GUM uncertainty framework slightly overestimates the overall uncertainty for the cases evaluated here. Although the GUM Uncertainty Framework proves to be adequate for the particular EMC tests that were considered, generally the Monte Carlo Method has features that avoid the assumptions and the limitations of the GUM Uncertainty Framework.

A compact symmetrical band-pass filter design using coupled microstrip line is presented in this paper. The microstrip line sections connected to the two input and output ports of the filter structure are printed over the Defected Ground Structure (DGS). The proposed symmetrical structure offers a simple and compact design and exhibits improved stop-band characteristics in comparison to the conventional coupled microstrip line filter structure. The prototype model of the proposed filter structure is developed and tested. The measured results are found to be in good agreement with the simulation results.

Ultrawideband (UWB) microwave imaging is a promising emerging method for the detection of breast cancer. Fibroglandular tissue has been shown to significantly limit the effectiveness of UWB imaging algorithms, particularly in the case of premenopausal women who may present with more dense breast tissue. Rather than trying to create an image of the breast, this study proposes to compare the UWB backscattered signals from successive scans of a dielectrically heterogeneous breast, to identify the presence of cancerous tissue. The temporal changes between signals are processed using Support Vector Machines to determine if a cancerous growth has occurred during the time between scans. Detection rates are compared to the results from a previous study by the authors, where UWB backscatter signals from a single scan were processed for cancer detection.

Japanese terrestrial broadcasting was completely converted to digital television (DTV) broadcasting on 470--710\,MHz as of July 2011. However, fading phenomenon resulting from standing waves is a factor in quality deterioration in TV and mobile communication technologies. Suppression of this is needed for many kinds of technologies. A broadband single-feed planar antenna composed of two antenna components, a Broadband Planar Monopole Antenna (B-PMA) and a Broadband Planar Slot Antenna (B-PSA), is proposed for reducing deterioration of reception due to the fading across the DTV band. Reflection coefficients and radiation patterns analyzed by the Finite Difference Time Domain (FDTD) method and compared with measured results indicate that the proposed antenna is broadband compared with a conventional antenna studied previously. A field experiment is conducted in the DTV band. The results of the field experiment indicate clearly that the proposed antenna efficiently suppresses fading resulting from standing waves across the band.

A comprehensive study is performed to investigate the performance of a non-uniform circular array interferometer in a real time 3-dimensional direction finder. The angular range of view is supposed to be 65 degrees vertically and 120 degrees horizontally, which is suitable for airborne applications. Interferometer is designed to work in the S, C and X bands. Regarding optimization process, the interferometer employs an eight element non-uniform circular array along with a phase reference antenna at the center of the array. Several quantities and parameters are studied, e.g., frequency behavior, origins of phase measurement errors, Signal to Noise Ratio (SNR) effect on phase measurement, and the effect of the phase measurement error on direction finding performance. The proposed interferometer is able to tolerate at least 35 degrees of phase measurement error. Radius of the array is determined to be 22 cm in order to have good frequency response in the desired frequency band. Both Generalized Regression Neural Network (GRNN) and Maximum Likelihood (ML) estimation are applied for mapping the phase relationships between antennas to the Direction of Arrival (DoA). The results of two methods are well matched, and therefore validation is performed.

The microwave transmission of hexagonal arrays consisting of patches of equilateral aluminium triangles has been experimentally studied as a function of metal occupancy (triangle size). As one would expect, at low frequencies the microwave transmission drops on passing through the connectivity threshold (50%) when the disconnected hexagonal array of metal triangles switches to a disconnected hexagonal array of equilateral holes. However, for higher frequencies resonant phenomena cause a complete reversal in this behaviour such that the transmission, on passing through the connectivity threshold, increases substantially.