We investigate experimentally and theoretically Ultra-Wideband (UWB) wireless transmission in different WPAN scenarios. Short-range UWB wireless link (wireless fire-wire) have been studied theoretically and experimentally. Different mutual positions and distances between the antennas have been investigated. It was found that the reactive antenna coupling might decrease power budget as much as 15 dB by an antenna separation of 5 mm.

A cylindrical wave expansion method is used to obtain the scattering field for a two dimensional cylindrical invisibility cloak incorporating perfect electromagnetic conductor (PEMC) at perturbed void region. A near-ideal model of the invisibility cloak is set up to solve the boundary-value problem at the inner boundary of the cloak shell. It is confirmed that a cloak with the ideal material is a perfect cloak by observing the change of the scattering coefficients from the near-ideal case to the ideal one. However, because of the slow convergence of the zeroth-order scattering coefficients, a tiny perturbation on the cloak would induce a noticeable field scattering. A better convergence rate of the scattering coefficients has been observed for decreasing δ in PEMC case.

In this paper, we propose several array topologies to achieve good power-combining characteristics for the open slot antenna. By utilizing an appropriate feeding structure and injecting in-phase or out-of-phase signals, power-combining radiation patterns can be derived. Simulated surface current distributions of several antenna structures are presented to explain radiation mechanism. From the results of radiation performance, the advantages of gain enhancement and pattern reconfiguration are shown. By varying the phase difference of two injected signals of the open slot antenna array, two-dimensional beam-scanning radiation patterns are successfully demonstrated.

A fast method for electromagnetic imaging from monostatic full rotational near-field scattering is proposed in this paper. It is based on circular spectrum theory which exploits the Fourier decomposition of the targets distribution instead of point by point imaging in earlier works. The novelty of the proposed method is that it simplifies the relationship between the spatial frequency domain and the scattering field. The near-field scattering is analyzed by expanding the distance to Taylor series at the centre of the targets zone. The near-field focus function is then transformed to spatial frequency domain and evaluated by the method of stationary phase. The imaging result is given by two-dimensional inverse Fourier transformation from spatial frequency domain of targets. The proposed method is validated by comparing the simulation results of distributed targets with the tomographic imaging. The dynamic range of imaging result is derived by distributed targets with different reflection coefficient. Furthermore, the experiment is also conducted in microwave chamber at Ku band with target placed on the turntable.

Radome has strong effects on the radiation performances of the antenna in millimeter wave band. In this paper, the aperture integration-surface integration (AI-SI) method is adopted to analyze the electrically large antenna-radome system. The fast multipole method (FMM) is proposed to accelerate the aperture integration and inner surface integration in the AI-SI method. An electrically large antenna-radome system at W band is analyzed and measured. The radiation patterns of the system calculated using the AI-SI method with and without the fast multipole acceleration and the measured patterns are compared. The calculated patterns agree very well with each other, and both have the same agreement with the experimental results. However, the computational time of the proposed analysis with the fast multipole acceleration is reduced significantly.

On the basis of backward coupling and left-handed microstrip line, new designs of duplexers and multiplexers will be presented and tested in different configurations. By using microstrip lines with Complementary Split Ring Resonators (CSRRs) etched on the ground plane along with series capacitive gaps in the upper conductor, forward coupling will be inverted into backward coupling. Compact size and fully planar fabrication techniques are important characteristics in the devices proposed.

A compact dual-band ortho-mode transducer is presented in this paper. Two orthogonally polarized signals received by a square waveguide are separated into two orthogonal channels at 10.7-12.75 GHz and 10.3-11.9 GHz, respectively, while a single-polarized signal is transmitted at 14-14.5 GHz. To obtain good isolation between the transmit (Tx) and receive (Rx) channels of the same polarization with a compact size, an irregularly shaped diaphragm is proposed as a compact dual-function resonator, which has one transmission zero at the Tx band and one pole at the Rx band. The designed OMT is fabricated and measured in a back-to-back configuration. Measured results agree very well with simulated ones and the isolation improvement by the diaphragm is about 15 dB, which verifies our design.

A new indoor facility for electromagnetic tests is presented and used here for the specific case of bistatic radar cross section (RCS) measurements. A metallic cube is selected as test case and the results are compared with the predictions obtained with different numerical methods. Good agreement is reported.

In this paper, we consider the problem of bistatic multiple-input multiple-output (MIMO) radar systems design for parameters estimation. Maximum channel capacity is used as criterion for the problem of optimal systems design under transmitted power constraint and channel constraint. We obtain that the system design based on maximum channel capacity can be expressed as a joint optimization problem. Given the number of transmit antenna, the number of receive antenna and signal-noise ratio (SNR), the maximum channel capacity can be determined. This maximum channel capacity can be obtained from a unique appropriate power allocation and antenna placement strategy, which is very important for system design.

A novel out-of-line series-fed patch array with low cross-polarization is presented in this paper. The element in the array is fed by a stub through one-port. The feeding stub is designed to be a novel curled-horn-shaped geometry, which can effectively suppress the cross-polarization due to its symmetry. The linear array consists of two identical subarrays which are located oppositely. By the antiphase feeding of two subarrays, the cross-polarization is further reduced. Furthermore, the theory analyses of the series-fed array indicate that it is competent for being applied to phased array systems. The simulated results show the cross-polarization levels of the linear array with 20 novel elements in E and H plane are lower than −30 dB and −60 dB, respectively. And, a prototype array is fabricated. Its low cross-polarization levels confirm the effective performance of the proposed design.

A compact double-balanced monolithic star mixer for Ka-band applications using 0.25 μm GaAs pHEMT process is presented. With multi-coupled lines technology, the proposed dual 180° hybrid is produced and applied to a star mixer successfully. The proposed hybrid adopts the power divider and two types of multi-coupled lines to improve the return loss and isolation at the balance outputs of a traditional dual Marchand balun. Output ports are allowed to locate arbitrarily, eliminating a complex layout while the dual 180° hybrid is applied to double balanced star mixers. As the measurement results show, the proposed mixer achieves an operation bandwidth of 27 to 36 GHz with the best conversion loss of 6.3 dB at 28 GHz. In addition, the chip dimension can be manufactured as small as 0.81 mm².

A tunable microwave notch filter is developed on magneto-dielectric material having low saturation magnetization to attain low external dc magnetic field for biasing. A simple microstrip line at 10 GHz is developed on nickel ferrite/low density polyethylene nanocomposite system as substrates and its microwave transmission response is studied in X-band. Composite system is developed by dispersing nano sized nickel ferrite (~6.63 nm) in low density polyethylene to obtain a homogeneous flexible substrate. Saturation magnetization of 4% volume fraction of the composite is found to be 1.8745 emu/g. Tunability of Q value and insertion loss is studied with magnitude of external dc magnetic field and at different angles of its orientation with the axial plane. A very low field up to 250 G is sufficient to tune the selectivity. An insertion loss of ~-30 dB and Q ~ 375 at 10.2 GHz is observed. The interaction of magneto static modes with orientation of the applied dc magnetic bias with respect to rf magnetic field is discussed with couple mode theory. Good cut-off behaviour of more than 28 dB is observed at magnetic field angles from 23.52° to 34.21°. The experimental and theoretical couplings show close proximity.

A novel approach for the design and optimization of spherical lens antennas (SLAs) including practical feed model (PFM) is proposed. The vector spherical wave function expansions (VSWE) combined with differential evolution (DE) algorithm is adopted for the optimal design of SLAs. Moreover, the near-field aperture distributions of a Ku band dielectric loaded horn feed and a Ka band corrugated horn feed were obtained using the full wave simulation and were then taken into account in the DE optimization. The performances of the optimized 2-layer design are compared with previous works, higher directivity is obtained. Additionally, the radiation characteristics of an optimized SLA are presented, and numerical results of a 650 mm diameter 2-layer hemispherical lens antenna (HLA) with ground plane are compared to the experimental results, and good agreements are obtained. An investigation of the influence of the various lens-to-feed distances as well as aperture sizes of SLA on the aperture efficiency for a 2-layer design is also proposed.

There are many applications of beam quality and beam shape in turbulent atmosphere. Because M² factor and kurtosis parameters are often used to descripe beam quality and intensity flatness, the evolution of these two parameters of Hermite-Gaussian beam in turbulent atmosphere have been studied in both theory and numerical calculation. Results show that the spectrum of refractive index fluctuations has a strong effect on these two parameters. For some spectral models, these two parameters are very sensitive to some factors of turbulence. But for other spectral models, the factor is very insensitive to these factors. For example, when the exponent of the spectrum is very small, M² factor is very insensitive to the outer scale of turbulence. But when the exponent of the spectrum is very large, the M² factor is very insensitive to the inner scale. In addition, we also found that there are many differences between the kurtosis parameters under different conditions. For example, the kurtosis parameters may be very large during propagation. Namely, beam shape may be very sharp under some conditions. When the effects of turbulence is very large or very small, beam shape is very flat.

The permittivity of extra thin silk cloth is usually measured through some complex methods in the past. Here we propose a convenient and flexible method to measure the permittivity of extra thin silk cloth using resonant metamaterial structures. The metamaterial structures used here are symmetric split ring resonators (SRRs). The principle is that the resonant frequency of the SRRs is very sensitive to the permittivity of the surrounding medium. Therefore, the relative permittivity of an extra thin medium as silk cloth can be determined. Our experimental measurement shows that the relative permittivity of the silk cloth is 4.5. A piece of printing paper is also measured with a relative permeability of 1.4. The effectiveness of the method in determining the permittivity of a solid medium is very useful in future applications.

The propagation equation, written in a curvilinear coordinate system, is solved by using a perturbation method inspired from quantum physics and extended to imaginary eigenvalues and evanescent waves. The parameter of perturbation is the groove depth which is small compared to the period. The method is expanded up to second order for the non-degenerate problem. In this way the solutions have analytical form compared to a numerical method. They present the advantage to put in evidence the evolution of the energy distribution for different diffraction orders as a function of the magnitude of the perturbation. The efficiencies which are deduced from these analytical solutions are compared of those obtained by the curvilinear coordinate method. The good agreement between the two methods occurs for a groove depth with respect to the wavelength less than or equal to 0.16. Thus, this new approach opens a new range of applications for inverse problems.

Conventional interferometric ISAR (InISAR) imaging requires a radar system with at least three antennas, and the hardware complexity may be a main obstacle to practical realization. In this paper, we propose an InISAR three-dimensional imaging algorithm using only one antenna. Interferometric processing is carried out among ISAR images obtained during three near measurement intervals. The scatterer position in the range direction is obtained from range cell number in ISAR images, and the azimuth/height information is estimated from interferometric phases and geometrical relationship. Moreover, the target track requirements of the proposed method are also investigated. Simulations have shown the effectiveness of the proposed method.

The design of concentric ring arrays for isoflux radiation is presented in this paper. This design considers the reduction of the side lobe level and isoflux radiation requirements for Medium Earth Orbit (MEO) satellites. The optimization problem considers the spacing among rings and levels of amplitude excitations. The well-known method of Particle Swarm Optimization (PSO) is utilized for this design case. The obtained results could cause the satellite hardware to be reduced significantly even more than that presented previously in the literature.

In the future, mobile handsets might incorporate more than 20 separate radios, creating a difficult antenna design problem due to the sever space restrictions. This paper proposes a reconfigurable wideband antenna, for use within clamshell mobile handsets. The impedance bandwidth of the new antenna was selected in order to meet current and future demands within the industry. It has been suggested that a portable Cognitive Radio must be capable of simultaneous communication (via a narrowband antenna) and spectrum sensing (via a wideband antenna). For this reason a narrowband slot antenna has also been integrated within the wideband radiator.

Conjugately characteristic-impedance transmission lines (CCITLs) are a class of transmission lines possessing conjugately characteristic impedances (Z₀^±) for waves propagating in the opposite direction. A typical Z₀ uniform transmission line is a special case of CCITLs whose argument of Z₀^± is equal to 0^o. This paper aims to generalize the CCITL system by demonstrating a theoretical study of CCITLs and their applications in the microwave transistor amplifier design. It is found that the bilinear transformation plays an important role in transforming circles in the reflection coefficient Г₀-plane in the Z₀ system to the Г-plane in the CCITL system. In addition, Meta-Smith charts, a graphical tool developed for solving problems in the CCITL system, are employed to design matching networks to achieve desired amplifier properties. Results show that stability regions on Meta-Smith charts can be determined, and source and load reflection coefficients can be selected properly to obtain desired operating power gain. In addition, an example shows that Meta-Smith charts offer a simple approach for matching network design using open-circuited single-stub shunt tuners.