Terahertz spectroscopy brings precious complementary information in life science by probing directly low energy bindings inside matter. This property has been demonstrated on dehydrated substances, and interesting results are obtained on liquid solutions. The next step is the characterization of living cells. We have successfully integrated THz passive circuits inside Biological MicroElectroMechanical Systems (BioMEMS). They are based on metallic wires called Planar Goubau Line (PGL). We demonstrate that high THz measurement sensitivity can be reached with new design based on spirals. But we show that the principal interest of this design is its high spatial resolution below the wavelength size compatible with living cell investigation.

Integration of multiple functions is for the first time achieved within a single patch element. Firstly, out of phase equal power division and bandpass filter characteristics are combined within a patch element. The novelty of the proposed structure is to use simple asymmetric cross slots in the patch element to achieve this integration. A simplified equivalent circuit model to describe operation of this patch element is proposed. Coplanar waveguide/microstrip broadside coupling is then investigated to enhance the performance of the patch balanced filter and eliminate narrow coupling gaps and microstrip lines. Subsequently, transition between microstrip and coplanar waveguide is then added to the patch element by using certain electromagnetic coupling methods for higher level integration without introducing additional loss. Different patch elements operating at 2.4 GHz are developed to validate the feasibility of the proposed structures. The circuits were designed, fabricated and measured. The measured results agree quite well with the simulation, exhibiting small amplitude and phase imbalance at the output ports throughout the desired passband, and good rejection levels elsewhere.

In this paper, a new technique is developed to evaluate efficiently the Sommerfeld integrals arising from the problem of a current element radiating over a lossy half-space. The annihilation of the asymptote and the branch-point singular behavior of the spectral Green's function is used in this technique. The contributions of the subtracted asymptotic and singularity terms are calculated analytically. The annihilation results in a remaining integral that is very smooth and can be calculated adaptively by using Gaussian quadratures and extrapolation methods to accelerate the convergence of the oscillating integrand. The accuracy and efficiency of the new technique has been confirmed by comparison with literature, and the commercial software NEC. The application of the proposed technique provides a robust and rapid procedure to calculate spatial Green's functions which can be used in ground-wave propagation, and lightning return stroke channel modeling.

Two microstrip fed ultra-wideband (UWB) antennas with different band rejection techniques are presented in this paper. The designed antennas consist of a defected ground plane with an elliptical slot and two different radiator shapes. The first design is composed of a half circular ring radiator element while the second one uses a crescent shaped radiator. The radiators are fed by a 50 Ω microstrip line with a tapered microstrip transition to ensure good impedance matching. The calculated impedance bandwidth of the proposed antenna ranges from 3 GHz to 14 GHz with relatively stable radiation patterns. To achieve band-notch characteristic in the 5.0--6.0 GHz WLAN frequency band, two different techniques have been implemented. The first technique uses a C-shaped slot etched in the ground plane while the other one uses another Cshaped slot in the feed line.

In this paper we present a new method for the design of multi-band microstrip filters. The proposed design method is based on Differential Evolution (DE) with strategy adaptation. This self-adaptive DE (SaDE) uses previous experience in both trial vector generation strategies and control parameter tuning. We apply this algorithm to two design cases of dual and tri-band filters for WiFi and WiMax applications. We select the Open Loop Ring Resonator (OLRR) filters, which are comprised of two uniform microstrip lines and pairs of open loops between them. The results indicate the advantages of this approach and the applicability of this design method.

The scattering of an oblique electromagnetic wave incident on a sub-wavelength circular pore with a finite depth on the surface of a semi-infinite perfect conductor is investigated analytically. We use the method of matched asymptotic expansion to find the multipole structure. The expansion is based on the duality property of the source-free Maxwell equations, and the resultant scattering fields are fully expressed in terms of the scalar and the conjugate vector potentials. There are two regions defined by the analytical method: the electro/magneto-static inner region and the radiation outer wave region. For both TM and TE incidences, the scattering waves are lead by leading dipoles. In the next order of the scattering waves, a mixture of the dipole, the quadrupole and the octupole is found. This is a striking finding, that the multipoles are not organized in a strictly ascending manner when the size of the pore is considered. In addition, the sophisticated three-dimensional interplay of the multipoles, the pore depth, and the incident angle is revealed. The magnitudes of the scattering dipoles are confirmed convergent smoothly to those of the back-scattering dipoles of electromagnetic waves transmitted through a hole in a perfect conducting plate with a finite thickness when the pore depth is larger than about 1, normalize to the pore radius.

The authors suggest the generalized method of induced electromotive forces (EMF) for the investigation of the characteristics of single and systems of thin impedance vibrators at their arbitrary excitation and distribution of the surface impedance on the ground of the made analysis in the pro-posed paper. The distinctive peculiarity of this method is the use of the approximating functions, re-sulted from the integral equation solution for the current by means of the asymptotic averaging me-thod, in the current distribution along the impedance vibrator.

A rectangular dielectric resonator antenna (DRA) based on Barium Strontium Titanate --- Cyclic Olefin Copolymer (BST-COC) composite for 2.4 GHz wrist application is designed and characterized. The dielectric properties of the composite with ~57 vol.% BST loading are characterized using microstrip ring resonator structures at 2.45 GHz frequency. The proposed DRA, fixed onto a reverse grounded FR4 laminate, has a very compact size of 19 mm×10 mm×5 mm. The impact of the user's body proximity on the radiation performance of the antenna is studied experimentally. The percentage total efficiency and gain of the antenna deteriorated by about 8.5% and 2 dB due to the proximity of the user's body. The proposed DRA showed better performance than that of resonant type of antennas when close to the user's body.

A non-resonant microwave method has been proposed for accurate and stable constitutive parameter measurement of low-loss dispersive and non-dispersive isotropic materials. The method uses transmission-only measurements of two configurations: a) the sample inside a sample holder and b) the sample backed by a reference sample inside the same holder. It is not prone to undesired ripples in the extracted constitutive parameters arising from measured similar reflection properties. In addition, its accuracy is higher since it is not much affected by surface roughness and/or unevenness of the sample or the reference sample. It is based on frequency-by-frequency extraction and thus suitable for dispersive materials. However, it requires the selection of an appropriate reference sample. The method has been validated by measurements at Xband (8.2--12.4 GHz) of a low-loss sample located into a waveguide sample holder.

Apertureless scanning near-field optical microscopy (A-SNOM) with a superlens is a novel nano-optical system for sub-wavelength imaging purposes. This study presents a quantitative model for analyzing the heterodyne signals obtained from an A-SNOM fitted with a superlens at various harmonics of the AFM tip vibration frequency. It is shown that the image resolution is determined not only by the tip radius, but also by the superlens transmission coefficient in the high evanescent wave vector K_x. Moreover, the analytical results show that the images acquired from the A-SNOM/superlens system are adversely affected by a signal contrast problem as a result of the noise generated by the tip-superlens interaction electric field. However, it is shown that this problem can be easily resolved using a background noise compensation method, thereby resulting in a significant improvement in the signal-to-background (S/B) ratio. The feasibility of utilizing the system for maskless nanolithography applications is discussed. It is shown that the A-SNOM/superlens system with the proposed noise compensation scheme yields a dramatic improvement in the signal intensity and S/B ratio compared to that of a conventional A-SNOM with a bare tip only.

Synthetic Aperture Radar (SAR) can obtain a two-dimensional image of the observed scene. However, the resolution of conventional SAR imaging algorithm based on Matched Filter (MF) theory is limited by the transmitted signal bandwidth and the antenna length. Compressed sensing (CS) is a new approach of sparse signals recovered beyond the Nyquist sampling constraints. In this paper, a high resolution imaging method is presented for SAR sparse targets reconstruction based on CS theory. It shows that the image of sparse targets can be reconstructed by solving a convex optimization problem based on L1 norm minimization with only a small number of SAR echo samples. This indicates the sample size of SAR echo can be considerably reduced by CS method. Super-resolution property and point-localization ability are demonstrated using simulated data. Numerical results show the presented CS method outperforms the conventional SAR algorithm based on MF even though small sample size of SAR echo is used in this method.

A new broadband circularly polarized (CP) square slot antenna is evaluated numerically and verified experimentally. The proposed antenna uses a lightening-shaped feedline protruded from the signal line of the feeding coplanar waveguide (CPW). Two symmetrical F-shaped slits embedded in opposite corners of ground plane are designed to obtain an excellent CP bandwidth. By adjusting the dimensions of the lightening-shaped feedline, the CP bandwidth can be further enhanced. Measured results show that the 3-dB axial-ratio bandwidth of the proposed antenna can reach 51.7% (2150 MHz-3650 MHz), and the impedance bandwidth is as large as 60.2% (2150 MHz--4000 MHz) with VSWR ≤ 2. Measured results are in good agreement with the simulation. The proposed antenna can be easily fabricated because of the simple coplanar geometry.

A fully fabric triangular shaped microstrip patch antenna is proposed for Wireless Broadband (WiBro) communication systems operating in the frequency range of 2.3 GHz to 2.4 GHz with 2.34 GHz as centre frequency. Three highly efficient and flexible antennas, built using three different conductive fabrics and an insulating polyester fabric are evaluated and results reported in this paper. To the best of authors' knowledge, this is the first attempt to utilize textile materials for the development of WiBro antennas.

A helix slow-wave structure (SWS) for a high efficiency Ku-band 140 W space TWT has been designed. Cold circuit parameters of helix SWS like propagation constant and on axis interaction impedance were determined using 3-D electromagnetic field simulators ANSOFT-HFSS and CST-MWS and validated with the experimental results. In-house developed large-signal code SUNRAY-1D was used to design the complete helix SWS in 2-section with sever and taper to achieve desired output power, gain, efficiency, and other linearity parameters such as phase shift, AM/PM factor, I/M components. Simulated RF performance of the Ku-band 140W helix TWT was validated with the experimental results. A close agreement between the simulated and experimental results has been found.

Excitation of electromagnetic ion-cyclotron instability in the magneto plasma in the presence of perpendicular A.C. electric field for a generalized distribution function for background cold electrons and hot ion plasma has been studied. This distribution function is reducible to anisotropic and loss-cone type for different values of spectral index j. The particle trajectories have been estimated and used to find the dispersion relation and growth rate by using the method of characteristic solutions. Temporal electromagnetic ion cyclotron instability for various plasma parameters has been studied. The role of choice of parameters, distribution function and simultaneous presence of a.c. electric field is studied for excitation of electromagnetic ion cyclotron instability. The results have been used to explain the satellite observations of AMPTE/CCE and compared with earlier work done for temperature anisotropy and other types of distribution functions using other techniques.

The reliability of circuits on printed circuit boards (PCBs) in many modern electronic products is affected by severe noise caused by high-speed and low-voltage operation as well as layout constraints compounded by limited space and high circuit density. Crosstalk is a major noise source that interferes with the signal integrity (SI) in poor PCB layout designs. One common method of reducing crosstalk is the three-width (3-W) rule. The serpentine guard trace (SGT) approach has also been used to reduce crosstalk using two terminal matching resistors on the SGT between the aggressor and victim. Although the SGT approach suppresses far-end crosstalk (FEXT) at the expense of more layout space, it also neglects interference caused by near-end crosstalk (NEXT). In this study, we propose the SGT via (SGTV) approach in which grounded vias are added to the SGT at appropriate locations, and the ratio between the lengths of the horizontal and vertical sections of the guard trace is adjusted to minimize NEXT and FEXT. Frequency domain simulated (measured) results showed that the SGTV approach reduced NEXT by 3.7 (7.65) and 0.83 (1.6) dB as well as FEXT by 5.11 (7.22) and 0.1 (1.98) dB compared to the 3-W and SGT approaches, respectively. In the time domain, simulated (measured) results showed that SGTV reduced NEXT by 34.67% (49.8%) and 27.5% (26.65%) as well as FEXT by 46.78% (56.52%) and 6.91% (24.8%) compared to the 3-W and SGT approaches, respectively. Our proposed approach thus effectively suppresses both NEXT and FEXT to achieve better SI in PCB layout designs than the other two methods. As our design uses two grounded vias instead of two guard trace terminators and does not require extra components, it is less costly than SGT. Our simulated and measured results indicate that our approach is suitable for practical application because of the lower cost and the ease of implementation that eliminates NEXT and FEXT.

Scattering of electromagnetic radiation by a charged homogeneous spherical particle/body is treated. Theoretical solution represents a generalization of the Mie's scattering theory for electrically neutral sphere. It is shown that classical and quantum physics approaches may lead to different conclusions, as documented by numerical computations assuming various permeabilities, refractive indices, surface charges, temperatures, and other physical parameters of the spherical particles. Two discrete wavelengths (5 μm and 1mm) of the incident radiation are considered. Optical properties of charged particles composed of absorbing and slightly absorbing materials can essentially differ. Especially, the resonance peaks typically occur when imaginary part of particle refractive index is low. The relative permeability of a material may differ from unity at large wavelengths, e.g., in microwave region. Basically, the relative permeability appears to be less important factor than the surface charge. However, the permeability can influence the scattering and extinction efficiencies, as well as the backscattering features of small particles, under some conditions.

A compact multiband (GSM/DCS/PCS/UMTS/Bluetooth/WLANs/ Wi-MAX) planar monopole antenna, which contains multiple branches, is proposed in this work. Most wireless communication bands for consumer electronics are covered in this design. The antenna radiator comprises four resonant branches on the top surface of a PCB board and one parasitic element on its back. The antenna size is 17.5 mm×35.7 mm, and no via is needed in the fabrication process. Various techniques, such as branching, meandered lines, closed loop, capacitive coupling, parasitic elements and tapered ends, are used to enhance the antenna's bandwidth, matching and size reduction performance. Simulation and measurement show good agreement for reflection coefficient. The proposed antenna is particularly attractive for mobile devices that integrate multiple systems.

Two extended doublet bandpass filters with compact size and good spurious suppression characteristic are proposed. One is built up by a dual-mode microstrip resonator with a full-mode substrate integrated cavity, while the other is composed of a microstrip resonator and a half-mode cavity. The relationship between the location of their transmission zeros and the impedance ratio of the microstrip resonator is analyzed theoretically. Our proposed filters only occupy the areas of 0.69λ₀²/ε_r and 0.51λ₀²/ε_r, and they also have wide upper stopband. The predicted performances are demonstrated by the reasonable agreement obtained between their simulated and measured S-parameters.

Scattering of electromagnetic plane waves from an infinitely long nihility cylinder, coated with a chiral layer of uniform thickness, is presented. Cylindrical vector wave functions have been used to express the fields in different regions. The solution is determined by solving the wave equation for different regions and applying the appropriate boundary conditions at the discontinuities. Both TM and TE polarizations as incident plane wave have been considered in the analysis. Obtained Numerical results for the chiral-coated nihility cylinder are compared with a chiral-coated PEC cylinder.