A coplanar-strip dipole antenna with two enhanced features is presented for broadband circular polarization (CP) operation. The first feature of the proposed antenna is the replacement of a conventional thin dipole by a wide strip, resulting in two degenerated orthogonal modes to make CP operation possible. The second one is the use of two coplanar strips instead of two non-coplanar ones, thereby giving rise to the advantages of easy implement, good impedance matching, and wide axial ratio (AR) bandwidth. Two examples are given, one for the lower band around 1.8 GHz and the other for the ultra-wideband (UWB). For the lower band, the measured -10 dB return loss (RL) bandwidth is 119% (0.74 to 2.93 GHz), and the measured 3 dB AR bandwidth is 50% (1.45 to 2.41 GHz). As for UWB, the measured RL is below -10 dB between 2.1 to 10.1 GHz, and the measured AR is below 5 dB between 4.1 to 7.75 GHz.

A compact-size planar antenna with ultra-wideband (UWB) bandwidth and directional patterns is presented. The antenna can be fabricated on a printed circuit board (PCB). On one side of the PCB, it has a circular patch, and on the other side it has a slot-embedded ground plane with a fork-shaped feeding stub in the slot. Directional radiation is achieved by using a reflector below the antenna. To reduce the thickness of the antenna, a new low-profile antenna configuration is proposed. Three types of directional UWB antennas are analyzed. The distance between the antenna and the reflector is 12 mm (0.16 λ₀, λ₀ is the free space wavelength at the lowest frequency). In order to validate the design, a prototype is also fabricated and measured. Measured results agree well with the simulated ones. The measured results confirm that the proposed antenna features a reflection coefficient below -10 dB over the UWB range from 4.2 GHz to 8.5 GHz, a maximum gain around 9 dBi, a front-to-back ratio over 17 dB and pulse fidelity higher than 90% in the time domain. Thus it is promising for see-through-wall imaging applications.

Some interesting results are presented in this paper by investigating the characteristics of square high-order mode cavities. Based on the standard printed circuit board (PCB) process and the substrate integrated waveguide (SIW) technology, two different square cavities which exhibit dual-mode filtering response are studied and implemented. Their bandwidths can be controlled by adjusting the eigen-frequencies of the resonating modes and the coupling apertures. The proposed configurations also allow implementing transmission zeros to improve the selectivity in an easy way. A Q-band quasi-elliptic filter using such two cavities in a folded configuration is designed, fabricated and measured. High selectivity and small insertion loss are achieved which are in good agreement with the simulated results.

In this paper, we present a novel approach for improving the bandwidth of a microstrip patch antenna using Jerusalem cross-shaped frequency selective surfaces (JC-FSSs) as an artificial magnetic ground plane. The invasive weed optimization (IWO) algorithm is employed to derive optimal dimensions of the patch antenna and JC-FSS element in order for the whole structure to work at 5.8 GHz with consideration of gain. For the most efficient design, the antenna and FSS ground plane are optimized together, rather than as separate components. Simulation results demonstrate that this optimum configuration (the microstrip patch antenna over the artificial magnetic ground plane) have a broad bandwidth of about 10.44%. This wide bandwidth is obtained while the thickness of the whole structure is limited to 0.1λ. Further more desirable radiation characteristics have been successfully realized for this structure. The radiation efficiency of the AMC antenna configuration was found to be greater than 85% over the entire bandwidth. In general by introducing this novel Jerusalem cross artificial magnetic conductor (JC-AMC) in lieu of the conventional perfect electric conductor (PEC) ground plane, the bandwidth enhancement of about 67% and a thinner and lighter weight design has been obtained. Sample antenna and EBG layer are also fabricated and tested, to verify the designs. It is shown that the simulation data in general agree with the measurement results for the patch antennas implemented with FSS ground plane.

In this paper, we will study the influence of nonlinear waves (breaking waves) on the EM signature of a sea surface in bistatic case (forward propagation). Indeed, we will start the temporal numerical analysis of the scattering coefficient σ_HH of breaking waves in bi-static configurations. Then, we will show the first experimental validation of the numerical results using well calibrated measurements of precise breaking wave profiles. These experimental measurements have been carried out in X-band in our anechoic chamber(E³I²-EA3876-ENSTA BRETAGNE). In this work, we will consider the sea surface as a perfect conductor.

We have calculated the photonic bands of a dispersive and lossy periodic array of left-handed metamaterial layers in air. Depending on the behavior of the fields inside the metamaterial component, two categories of modes for oblique propagation are identified: the oscillatory and the tunneling modes. In order to characterize these two types of solutions, we calculate the complex photonic bands; a criterion of penetration-limit is introduced to quantify the absorption effects. Our results show that oscillatory TE and TM waves can be excited by light incident from air at low frequencies (within the metamaterial regime). In the region of high frequencies only TE tunneling modes are available. To complement the description of the absorption effects, we present transmission spectra and field profiles for TE waves in finite layered systems the two types of modes here studied.

This paper proposes a miniaturization method for conventional Wilkinson Power Divider(WPD) by replacing the quarter wave sections with the help of fractals. The performance degradation is compensated by using Defected Ground Structure (DGS). The resultant device occupies 56% of the area in comparison to the conventional WPD. The simulation results show a reflection coefficient of -66.98 dB and isolation of 24.1021 dB at the centre frequency of 1.8 GHz. Finally a prototype model is developed on a low cost FR4 Glass Epoxy substrate and tested. The experimental results show a good agreement with the simulation results.

This study reports on tunable planar metamaterial design that is capable to achieve dual-band negative index of refraction responses operating in microwave regime. Its distinctive characteristic is the usage of tuning open stub-loaded stepped-impedance resonators. Parameters retrieval algorithm, and full-wave simulation of prism-shaped structure were carried out to validate the negative refraction characteristics of metamaterial structure. The results predict its prospect as a very promising alternative to the conventional ones, which is compatibly applicable on various potential microwave devices especially when dual-band function is required. In addition to that, its design flexibility offers a various frequency bands at any possible choice, which is alterable together with any design parameters changes.

A tri-band four-element MIMO (multiple-input-multiple-output) antenna with high isolation is presented. The MIMO antenna consists of four symmetrical antenna elements. To relieve the degradation of the operation bandwidth caused by the strong mutual coupling among the four antenna elements, four symmetrical rectangles are removed from the four corners of the ground plane, respectively. The effect of the cutting of the four rectangles on the isolation is slight. Two kinds of isolation structure are applied to reduce the mutual coupling among the elements. The first kind of isolation consists of two slits and a protruded ground branch, and the second kind of isolation structure consists of four symmetrical slits etched into the ground plane. The mutual coupling caused by surface currents is reduced by slits, the mutual coupling resulted from near-field is suppressed by the ground branches, and thus high isolation for the MIMO antenna is achieved. Moreover, the effects of the slits and the ground branches on the operation bandwidth are slight, thus the operation bandwidth and the mutual coupling can be controlled independently, to some degree. A tri-band operation bandwidth (2.34-2.95 GHz, 3.38-3.75 GHz, and 4.4-6.7 GHz) with VSWR ≤ 2 and isolation ≥ 20 dB, is achieved. The results, including S-parameters, radiation patterns, mean effective gain (MEG), radiation efficiency and signal correlations, indicate that the proposed MIMO antenna can provide spatial or pattern diversity to increase data capacity of wireless communication systems.

Terahertz dielectric spectroscopy permits the study of biomolecular interactions. However, water induces high attenuation of electromagnetic waves in the THz frequency range, obscuring the response of biomolecules. The developed sensor overcomes this problem by concentrating the THz wave propagating in an integrated waveguide on a small liquid volume contained within a capillary tube. Detailed electromagnetic modeling shows effective interaction between the THz waves and liquids. Transmission measurement results for capillary tubes filled with water and methanol mixtures demonstrate a substantial increase in sensitivity to changes of liquid permittivity. The current integrated sensor facilitates THz spectroscopy of biological liquids: a case study on buffered human serum albumin solution demonstrates a great potential to complement biochemical analytical tools.

A novel planar ultra wideband (UWB) antenna using a second iteration Sierpinski carpet fractal shape with circular boundary is presented in this paper. The antenna covers the frequency band from 3 GHz to 12 GHz (VSWR ≤ 2). The proposed antenna has a meander shaped slot that renders the capability to reject 5.15-5.825 GHz band assigned for IEEE802.11a and HIPERLAN/2. The gain is suppressed very well in the desired WLAN bands. The measured antenna peak gain varies from 1.85 dBi to 6 dBi within the band. The time domain characteristics show that the antenna is not dispersive. A fabricated prototype is developed with close agreement between simulated and measured resonance as well as radiation characteristics.

Estimation and mitigation of multipath error improves the positional accuracy of GPS. The objective of this paper is to estimate the effect of multipath interference at the receiver antenna based on both code and carrier phase measurements using Code minus Carrier (CMC) technique, and suggest a suitable method to mitigate it for static applications. Different adaptive filters such as Least Mean Squares (LMS) and various Recursive Least Squares (RLS) are considered to mitigate the error. The estimated multipath error for a typical signal is 0.8 m and 2.1 m on L₁ and L₂ carriers, respectively. The results due to adaptive filtering methods are encouraging and significant reduction of error (cm level) is observed. It is found that, when compared with experimental static dual frequency GPS receiver data, LMS and RLS filters give better error minimization on L₁ and L₂, respectively.

This paper derives some optimum transmit and receive antenna coefficients in wireless multipath channels based on the spherical vector wave multimode expansion of the multiple-input multiple-output (MIMO) channel matrix. The derived antenna coefficients satisfy the following specific optimization criteria: (i) maximum MIMO mean effective link gain (link MEG) based on the multimode channel realizations or (ii) maximum MIMO link MEG based on the multimode correlation matrix or (iii) correlation minimization by diagonalization of the MIMO full-correlation matrix. It is shown that the proposed approach leads to matrix equations belonging to the nearest Kronecker product (NKP) problem family, which in general have no trivial solution. However, we show that exact solutions are provided to the posed NKP problems under the assumption of the Kronecker model for the MIMO full-correlation matrix. The results are illustrated by numerical examples. The proposed approach is a complement to existing antenna pattern analysis methods.

The classical problem for diffraction of a plane wave with an arbitrarily oriented wave vector at a strip is considered asymptotically by Wiener-Hopf method. The boundary-value problem has been broken down into distinct Dirichlet and Neumann problems. Each of these boundary-value problems is consecutively solved by a reduction to a system of singular boundary integral equations and then to a system of Fredholm integral ones of second kind. They are solved effectively by a reduction to a system of linear algebraic equations with the help of the etalon integral and the saddle point method.

In this paper, an ultra high frequency (UHF) low-profile antenna is proposed; it is based on the discone antenna but with addition of a back cavity, a short-circuiting structure and a two-plate top structure in order to achieve both low-profile and wideband. It is simulated and prototyped. The test results show that the antenna has an omni-directional radiation pattern in the horizontal plane, is of low-profile, has a height of less than 0.1λ_max, and is wideband with an impedance bandwidth of 65% from 430 MHz to 845MHz for VSWR < 2.5 and an impedance bandwidth of 43% from 440 MHz to 680 MHz for VSWR < 2.0. The proposed antenna can be easily flush-mounted on a planar surface and therefore has great potential for uses on aircrafts and high-speed trains due to its conformal capability.

Due to high-density routing under the CPU and DIMM areas, the original design of even and odd mode characteristic impedances changes. The occurrence of multi-drop problem between the CPU and memory chip causes over- and under-driven that reduce the eye opening. Furthermore, the different phase velocities of even- and odd-modes cause timing jitter at the receiver end. This paper proposes two steps to solve the complex issue of signal integrity for the multi-module memory bus. First, particle swarm optimization (PSO) is used to tune the characteristic impedance of the transmission line and on-die termination (ODT) values to improve transmission line impedance changes to obtain maximum power delivery. The fitness function of the algorithm is defined by selecting the minimum reflection coefficient at the driver side and maximum the transmission coefficient at the receiver side to reduce the over- and under-driven Second, the timing jitter can be reduced by placing a capacitor to compensate for the velocity difference caused by different propagation modes. Finally, signal integrity enhancements for the DDR3 are verified by measuring S parameters in the frequency domain and postprocessed eye diagrams in the time domain.

The effect of Kerr nonlinearity on a Lorentz beam is investigated by using the nonlinear Schrődinger (NLS) equation. Based on the variational method, the evolution of a Lorentz beam in a Kerr medium is demonstrated and the critical collapse powers of the Lorentz beam are derived. Numerical simulations of the propagation of a Lorentz beam in a Kerr medium show that the beam becomes quasi-circular in a very short distance. Although the beam width of the Lorentz beam broadens, the central part of the beam give rise to a partial collapse.

The novel TOPS mode can achieve wide swath imaging coverage at the cost of impaired azimuth resolution. MIMO-SAR systems combined with multi-channel SAR signal reconstruction in azimuth and digital beamforming (DBF) on receive in elevation can overcome the inherent contradiction between swath width and azimuth resolution of conventional SAR systems. This paper derives a novel spaceborne MIMO-TOPS mode for high-resolution ultra-wide-swath full polarimetric imaging. In such an imaging scheme, different polarimetric waveforms with different elevation beam pointing directions and short time delays are transmitted in a single pulse repetition interval (PRI) by different sub-aperture antennas in azimuth. Besides improving the desired signal-to-noise ratio (SNR) and suppressing ambiguous energy in elevation, a novel DBF on receive approach including two steps is adopted to separate different echoes corresponding to sub-pulses with different polarizations. The design example of a full polarimetric MIMO-TOPS SAR system, which allows for the imaging capacity to cover an ultra wide swath of 400 km with a high azimuth resolution of 3 m, is given to validate the proposed imaging scheme.

A new design for circularly polarized square slot antenna (CPSSA) is presented. The circular polarization operation in the proposed single-layer antenna is created through two equal sized crooked T-shape and an F-shape strips located on the patch. Compared to most of the previously reported CPSSA structures, the impedance bandwidth and the axial ratio bandwidth of the antenna are increased and also the size of the antenna becomes smaller. The presented CPSSA design has the compact dimensions of 40 x 40 x 0.8 mm³, total impedance matching bandwidth of 8.04 GHz and exhibiting a 28.03% (4.6-6.1 GHz) 3 dB axial ratio bandwidth. A prototype of the antenna is fabricated and tested, and a great agreement with simulated results is obtained.

In this paper, we propose a reference range correlation-based (RRcR) ranging technique suitable for low-power on-body wireless body sensor networks (WBSNs) via ultra wideband (UWB) radios. The proposed technique is based on the presence of reference nodes, and is assumed to have line-of-sight (LOS) links. We show that the performance of the proposed technique outperforms matched-filtering-based time-of-arrival (MF-TOA) estimators with no a priori and with perfect channel knowledge. We further show that increasing the number of reference node up to twenty provides significant enhancement in the performance traded for higher overall power consumption. Then, we study the effect of timing-misalignment on the Ziv-Zakai lower bound (ZZLB), and provide numerical results. The presented results are based on simulations in the IEEE 802.15.6a on-body-to-on-body channel (CM3) in the UWB band as well as actual measurements.