This paper deals with adaptive antenna array beamforming under spatial information uncertainties including steering angle mismatch, random perturbations in array sensor positions, and mutual coupling between antenna array sensors. To make antenna array beamformers robust against the spatial information uncertainties, we present an iterative method to obtain an appropriate estimate of the actual direction vector for each of the desired signals. The proposed method uses only the a posteriori information of the received array data. It invokes an appropriate objective function for estimation and solves the minimization of the objective function by using a gradient based algorithm. The convergence property of the proposed method is investigated. Simulation results are provided for showing the effectiveness of the proposed method.

In this work, a metasurface consisting of an array of circular holes in a metal conducting sheet with a sub-wavelength periodicity is considered. The surface partially reflects the incident field according to the shape and geometrical dimensions of the inclusions and, due to this property, is widely employed in antenna systems to improve the radiation pattern of regular radiators. Since the reflection properties of the metasurface are determined by the current density distribution on the metal, we inspect this distribution and coherently develop a new, easy, and accurate analytical model to describe the grid impedance of the metasurface. In order to validate the model, we compare the reflection coefficient of the array obtained through our approach to the one resulting from full-wave numerical simulations and to other accurateanalytical methods available in the open technical literature.

One of the main drawbacks of antenna integration on standard CMOS silicon substrates are the low radiation efficiency levels obtained due to the high silicon losses. This paper studies the use of micromachining techniques to remove silicon beneath the antenna as a solution to improve radiation efficiency. Several etching patterns are analyzed for different etching depths through simulations and measurements in order to find out which are the best ones for the micromachining process. Results are verified in two operating scenarios.

A novel compact dual-band bandpass filter using tri-section stepped impedance resonators (SIRs) is presented for Wireless Local Area Network (WLAN). SIRs and one stub between parallel couple line are employed to realize two satisfactory passbands. Meanwhile, one transmission zero is generated between the two passbands to achieve a high out-of-band rejection. Simulated results show that two central frequencies are located at desired 2.4 and 5.2 GHz with 3 dB fractional bandwidths of 6.3% and 3.4% respectively. The measured results are in agreement well with the simulated ones.

The efficient design of broadband turnstile junctions compensated with piled-up cylindrical metallic posts is discussed in this contribution. Very high relative bandwidths can be obtained, while maintaining the diameter of the input circular access port lower than the width of the rectangular waveguide ports, thus reducing the number of excited higher order circular waveguide modes. A novel full-wave analysis tool has also been implemented in order to reduce the CPU effort related to the complete design process.

In this paper, a novel double-band integrated antenna for applications in WLAN is presented and studied. Based on the mature dipole theory, radiation elements are printed on the two faces of a low cost FR4 substrate. The two dipoles are designed on the sides of the feedline, which can reduce the impact of each other availably. The distance between the two arms and the width of the arms plays an important role in improving the impedance matching. Furthermore, by folding the arms efficiently, the current distribution of the proposed antenna is extended, and the dimensions of the proposed antenna can be reduced. The size of the designed antenna is just 34mm×24mm×1mm (about 0.27λ×0.19λ×0.008λ, λ is the wavelength relative to the frequency 2.4 GHz). Moreover, the prototype of the antenna is constructed and tested, which shows a good agreement with simulated result. The measured bandwidths, ranging from 2.35 GHz to 2.61 GHz and from 4.7 GHz to 6.0 GHz respectively, are obtained with return loss less than -9.54 dB (about 2:1 VSWR). The proposed antenna covers 2.4/5 GHz WLAN bands, and radiation patterns with good omni- directional radiation in the operating frequency are observed.

A simple DoA estimator is proposed with a switched beam antenna. The estimator is implemented with an adjacent pattern power ratio algorithm. For a single source signal, the received signal powers are measured while the antenna switches over a set of measured directive beam patterns. The pattern that exhibits the maximum received signal power is chosen. Then, the ratio between the pattern adjacent to the chosen pattern and the chosen pattern, is used to find the DoA by using a lookup table or by performing a linear regression approximation. Compared with conventional DoA estimators with switched beam antenna, the proposed algorithm allows DoA estimation with low computational cost, without sacrificing much the estimation precision. Computer simulations and experiments in an anechoic chamber are carried out to verify the proposed algorithm with a switched beam antenna: the electronically steerable parasitic array radiator (ESPAR) antenna.

A novel single-layer broadband coplanar waveguide-fed antenna with band-rejected characteristic is proposed for WLAN/WiMAX operation. First, the broadband characteristic (2.43-5.97 GHz) is achieved by a CPW-fed patch antenna with a dual-Y slot. Then, a single slit is inserted on the radiating patch or ground plane to introduce a notched band. The proposed antenna has a compact size of 40 × 25 mm². The broadband characteristic and band-rejected functions of the proposed antennas are implemented and measured. Two types of antennas were studied. Measured notched-band impedance bandwidths (return loss <10 dB) are 370 MHz and 1050 MHz, respectively, which satisfies the requirements for WLAN and WiMAX applications. Detailed design steps and experimental results for the designs are studied and investigated in this paper.

An alternative analytical approach to calculate the weakly singular free-space static potential integral associated to uniform sources is presented. Arbitrary oriented flat polygons are considered as integration domains. The technique stands out by its mathematical simplicity and it is based on a novel integral transformation. The presented formula is equivalent to others existing in literature, being also concise and suitable within a singularity subtraction framework. Generalized Cartesian product rules built on the double exponential formula are utilized to integrate numerically the resulting analytical 2D potential integral. As a consequence, drawbacks associated to endpoint singularities in the derivative of the potential are tempered. Numerical examples within a surface integral equation-Method of Moments framework are finally provided.

Telecommunication systems integrated within garments and wearable products are such methods by which medical devices are making an impact on enhancing healthcare provisions around the clock. These garments when fully developed will be capable of alerting and demanding attention if and when required along with minimizing hospital resources and labour. Furthermore, they can play a major role in preventative ailments, health irregularities and unforeseen heart or brain disorders in apparently healthy individuals. This work presents the feasibility of investigating an Ultra-WideBand(UWB) antenna made from fully textile materials that were used for the substrate as well as the conducting parts of the designed antenna. Simulated and measured results show that the proposed antenna design meets the requirements of wide working bandwidth and provides 17 GHz bandwidth with compact size, washable and flexible materials. Results in terms of return loss, bandwidth, radiation pattern, current distribution as well as gain and efficiency are presented to validate the usefulness of the current manuscript design. The work presented here has profound implicationsfor future studies of a standalone suite that may one day help to provide wearer (patient) with such reliable and comfortable medical monitoring techniques.

In recent years, various attempts have been undertaken to obtain three-dimensional (3-D) reflectivity of observed scene from synthetic aperture radar (SAR) technique. Linear array SAR (LASAR) has been demonstrated as a promising technique to achieve 3-D imaging of earth surface. The common methods used for LASAR imaging are usually based on matched filter (MF) which obeys the traditional Nyquist sampling theory. However, due to limitation in the length of linear array and the ``Rayleigh'' resolution, the standard MF-based methods suffer from low resolution and high sidelobes. Hence, high resolution imaging algorithms are desired. In LASAR images, dominating scatterers are always sparse compared with the total 3-D illuminated space cells. Combined with this prior knowledge of sparsity property, this paper presents a novel algorithm for LASAR imaging via compressed sensing (CS). The theory of CS indicates that sparse signal can be exactly reconstructed in high Signal-Noise-Ratio (SNR) level by solving a convex optimization problem with a very small number of samples. To overcome strong noise and clutter interference in LASAR raw echo, the new method firstly achieves range focussing by a pulse compression technique, which can greatly improve SNR level of signal in both azimuth and cross-track directions. Then, the resolution enhancement images of sparse targets are reconstructed by L1 norm regularization. High resolution properties and point localization accuracies are tested and verified by simulation and real experimental data. The results show that the CS method outperforms the conventional MF-based methods, even if very small random selected samples are used.

An analytical approach based on linear periodic time-varying theory, is developed to analyze the noise characteristics of current-commutating CMOS mixers. Based on the derived transfer functions with memory effect of tail capacitance, the frequency-dependent noise transforming factors for individual stages in the mixers are numerically computed to rigorously describe the noise output. A unified noise expression considering both the thermal noise and the flicker noise is proposed. It enables the noise analysis of the mixers particularly for a high LO frequency with different IF characteristics, and is verified by measurements.

In this paper, a planar microstrip UWB monopole antenna with a good band-rejection is presented. By using a pair of arc shaped parasitic elements around the patch, an excellent notched frequency band for rejecting the WLAN band (5--6\,GHz) can be obtained. The arc shaped strips are parametrically studied and the effects of them on the radiation patterns and time domain behaviour of the UWB antenna are investigated.

The inter/extrapolation accuracy of the cubic polynomial method has been improved by optimizing three frequency samples for frequency-sweeping in the method of moments (MoM). In the method, the frequency samples are optimized by minimizing the global maximum of the polynomial component at the stationary points and two terminal points of the frequency band. The optimal frequency samples can be expressed as analytical forms of the two terminal points. Numerical examples are presented to validate the proposed method through comparison with the Pad\'{e} approximation.

Aiming at the enhancement of a non invasive Microwave Radiometry Imaging System's (MiRaIS) attributes, Left Handed Materials (LHM) with negative permittivity and negative permeability simultaneously, have been utilized. The optimization of the system focusing properties is being theoretically explored, implementing a semi-analytical Green's function technique and different matching structures. In the framework of this analysis the head is modeled by a double layered cylinder while a dielectric cylindrical layer consisting of LHM is placed on the surface of the human head model with a view to achieve focusing improvement inside the brain. Numerical code executions have been conducted for two different operating frequencies (0.5\,GHz and 1.0\,GHz) and for matching layers of various values of thicknesses and electromagnetic properties. The numerical results for the electric field distribution inside the head model, presented in this paper, verify that the LHM can provide an increased sensitivity of the system focusing properties and thus improve its overall performance.

A new method is introduced to construct a slab that has electric fields with propagation properties which are equivalent to a fractional-space wave equation in two-coordinate system. While its magnetic fields have propagation properties which are equivalent to the complementary fractional-space wave equation. Analytical forms for the reflection and transmission coefficients of this slab are derived. Results of these reflection and transmission coefficients show that such quasi-fractional-space slab has spatial and frequency selectivity properties.

This paper presents the design and implementation of a compact 2.4/5.2-GHz rat-race coupler on a glass substrate. Due to the low-loss substrate and thick metal layers, the process provides high-Q capacitors and inductors, and therefore the lumped rat-race coupler is practical. The coupler consists of three bandpass and one bandstop networks to achieve dual-band operations. The measured insertion losses at 2.4 GHz and 5.2 GHz are less than 2.7 dB and 1.9 dB, respectively. The measured return losses at the frequencies of interest are better than 20 dB. Moreover, the phase imbalances at the in-phase and anti-phase output ports are less than 3.9^o and 4^o at 2.4 GHz and 5.2 GHz, respectively. The chip size including all testing pads is merely 2.87 × 2.1 mm² which is comparable to on-chip levels.

A new double arrow head defected ground structure (DGS) with centered etched ellipse is proposed for designing a multilayer low pass filter (LPF) with wide rejection band and low insertion loss in the stop-band. The prototype LPF consists of three double arrow head DGS with centered etched ellipse in the ground plane and compensated capacitor on the top layer of a 30×40 mm² Roger RT/Duroid5880 substrate having relative permittivity (ε_r) of 2.2 and thickness of 0.78 mm. The cutoff frequency is equal to 1.07 GHz .The prototype LPF is then realized as multilayer structure to enhance the filter response and reduce its size. The size reduction of the proposed multi-layer LPF is about 26% more than the conventional one. The proposed filter has been fabricated and measured. Good agreement is achieved between the simulated and measured results. The filter presents the advantages of compact size; low insertion loss and high out-band suppression. Finally, the multilayer LPF is transformed to band pass filter (BPF) using J-inverter method.

This aricle reports the effect of vapour chopping technique on the properties of vacuum evaporated poly (3-methyl thiophene) thin films such as surface morphology, optical transmittance, band gap, refractive index and optical transmission loss. Vapour chopping gives smooth surface morphology with smaller grain size reduced roughness than non chopped thin films, while the transmittance of the thin film increases with simultaneous decrease in the refractive index, band gap and optical transmission loss decreases due to vapour chopping.

Folded wire load antennas with matching network are designed by using optimization algorithms. The loads are parallel capacitor/inductor/resistor circuits that are adjusted by means of Differential Evolution (DE) optimizers to maximize bandwidth and the matching networks. The measured voltage standing-wave ratio (VSWR) of the load folded dipoles confirms broadband performance and agrees with data obtained from moment method computations. Antennas having bandwidth ratio of 2.5 : 1, with measured VSWR less than 3.5, meets the requirement.