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.

This paper presents a novel conformal end-fire antenna whose design employs the Competitive Algorithm of Simulating Natural Tree Growth. This algorithm is based on the idea of simulating the processes of growth and wilting of natural trees and can search from simple to complicated structures with rapid convergence. Four optimized radiation elements were designed on a cross structure to verify the performance of the algorithm. A prototype of the designed antenna was also fabricated and tested. The antenna resonates at the center frequency of 2.45 GHz, exhibiting an ideal end-fire property. In addition, the measured and simulated results are in good agreement. Finally, we propose a novel end-fire antenna array based on the cross structure, with a radiation gain reaching 17.6 dBi.

This paper proposes a newly designed compact coplanar-waveguide-fed wideband circularly polarized (CP) printed square slot antenna (PSSA), in the square slot of which are a halberd-shaped feeding signal line and a square ring patch. By placing a specially designed metal reflector behind the bidirectional CP PSSA, one can obtain unidirectional CP patterns with a associated 3-dB axial-ratio bandwidth (ARBW) almost the same as that of the bidirectional antenna. The bidirectional L- and S-band PSSAs designed on FR4 substrates have 3-dB ARBWs as large as 25.3% and 29.1%, respectively. For the L-band antennas, the unidirectional design yields a 3-dB ARBW of 25.7% and a gain of about 3 dB higher than that of the bidirectional counterpart. In all these 3-dB axial-ratio bands, impedance matching with VSWR ≤ 2 is also achieved. Most importantly, the design concepts, procedures, and rules for the proposed antenna are presented in detail.

Based on linear optical transformation method, a diamond shaped reciprocal cloak with perfect invisibility in a certain direction is proposed. Compared with traditional cloaks, the object hidden inside the reciprocal cloak is not blind and can receive information from the outer region. Moreover, the reciprocal cloak is constructed of nonsingular homogeneous material parameters with reduced anisotropy that is relatively easy for practical realization. Full wave simulations validate the performance of the cloak.

A compact wideband dual-frequency microstrip antenna is proposed in this paper. By employing an offset microstrip-fed line and a strip close to the radiating edges in the circular slot patch, an antenna operating at dual frequency with the impedance bandwidth of 26.2% and 22.2% respectively is presented. By attaching a strip to the radiating edges opposite to the microstrip-fed line, this alters the current distribution and radiation on the antenna at the second resonant frequency. The second frequency is also tunable by varying the lengths of the microstrip-fed line. It is demonstrated that the proposed antenna covers the widebands of UHF and microwave for RFID application. A good agreement is obtained between the simulated and experimental results.

Design, simulation, and implementation of low profile microstrip spiral inductors for high power Industrial, Scientific and Medical (ISM) applications at the high frequency (HF-3-30 MHz) range are given for the first time. An accurate analytical model and algorithm have been developed to determine the simplified lumped element equivalent model parameters for spiral inductor and its physical dimensions. Five different spiral inductors are then simulated with a planar electromagnetic simulator using the physical dimensions obtained for the desired inductance values with the analytical method. The implementation method and substrate selection for spiral inductors at the HF range are given in detail for high power applications. The spiral inductors are then constructed on 100 mil Alumina substrate and measured with network analyzer. It is found that analytical, simulation and measurement results are in close agreement and the analytical method and algorithm that have been developed can be used to accurately determine the physical dimensions, and the resonant frequency of the spiral inductor for the desired inductance value.

This paper introduces a novel design of Butler matrix in substrate integrated waveguide (SIW) technology with wide frequency band characteristics. Butler matrices are particularly useful in advanced antenna design and characteristics such as wideband operation, power handling, manufacturing, integration, cost, etc. are typical issues to be addressed in many applications. The proposed planar 4×4 Butler matrix provides an interesting solution to most of these issues. Wideband operation is achieved thanks to improved cross-couplers. These components are also characterized by higher power handling when compared to $E$-plane couplers. The use of SIW technology enables to reduce insertion losses compared to other printed technologies, while maintaining most advantages of such technologies such as high integration, manufacturing simplicity, low weight, etc. The proposed design is fully described, from the elementary building blocks to the full assembly performances. The design is optimized for operation in Ku-band with a center frequency at 12.5 GHz. A prototype of the 4×4 Butler matrix is manufactured, and good performances are confirmed over 24% relative frequency bandwidth. Potential use of this sub-system in multibeam antenna design is also discussed.

There is increasing interest in electromagnetic interference (EMI) shielding due to the serious electromagnetic environment pollution caused by the continuously increased use of the electrical products and electronic devices. Electrical conductivity and EMI shielding effectiveness (SE) of composite materials made from silicone rubber with carbon powder and ferrite powder have been studied in microwaves and terahertz frequency ranges and the results are presented in this paper. In microwaves range, samples with higher electrical conductivity show a small variation of shielding performance with frequency, whereas the performance of samples with lower conductivity falls away with increasing frequency. It is shown that the variation of attenuation with frequency relates to the conductivity of the material.

Because of the asymmetry of six-port junctions and the nonlinearity of diode detectors, the calibration of direction finding receivers have to be carefully considered. It is generally believed that an efficient tool for numerical approximations, the artificial neural network (ANN), may be used for such calibrations. In this paper, a new calibration technique based on the ANN is proposed for direction finding receivers at a bandwidth of 1 GHz. The direction finding system adopts a zero-intermediate frequency receiver architecture, which offers the advantage of fast response times. The key modules of this receiver consist of two six-port networks used to measure phase differences and operating frequencies. The results indicate that the calibration technique achieves a high accuracy of 0.192°.

This paper presents the design of a broadband circular polarization truncated horn antenna with single feed. It does not require any complex feeding structure and uses only a coaxial feed extended with a simple electric field coupling probe. The corners of the horn are truncated to generate circular polarization modes, and a broad axial ratio bandwidth which is insensitive to the probe feed dimension is achieved. Simulated and measured results of an S band truncated horn antenna are presented. The antenna has a broad 3 dB axial ratio bandwidth of 26% with aperture efficiency of 60%.

Whole-body averaged specific absorption rate (WBA-SAR) is used as a metric for human protection from whole-body exposures. The frequency at which the WBA-SAR becomes maximal is called ``resonance frequency''. The present study proposes a scheme to estimate WBA-SAR at the resonance frequency based on an analogy between a human and a quarter-wavelength monopole antenna. Specifically, WBA-SAR can be estimated with the human body resistance once ankle current was obtained. Thus, it is essential to investigate the effective resistance for anatomically-based human models. Then, the effective resistances for different humans grounded on the perfect conductor are calculated to clarify the variability. The main factors for the variability were attributed to the body shape and model anatomy. In particular, WBA-SARs in human models grounded are found to be estimated from their BMI and respective measured ankle current in realistic environment, including a scenario of multiple wave exposure.

Microwave radar and microwave-induced thermoacoustic technique exploit the contrast in the permittivity and conductivity between malignant and healthy tissue. They have emerged as promising techniques for detecting breast cancers. This paper compares the imaging capability of these techniques in the presence of homogeneous and heterogeneous breast tissue. Relying on the data from the finite-difference time-domain simulations, the study shows that both techniques are capable of imaging homogeneous objects. In the presence of electromagnetic dispersion and heterogeneity, radar signals suffer from strong dispersion and multiple scattering, which decorrelate the signals with the scatterers. The microwave-induced thermoacoustic technique takes the advantage of breast being acoustically homogeneous and is capable of generating high-quality images.

In this paper, a new radar constant false alarm rate detector to perform adaptive threshold target detection in presence of interfering targets is proposed. The proposed CFAR detector, referred to as Adaptive Linear Combined CFAR, ALC-CFAR, employs an adaptive composite approach based on the well-known cell averaging CFAR, CA-CFAR, and the ordered statistics, OS-CFAR, detectors. Data in the reference window is used to compute an adaptive weighting factor employed in the fusion scheme. Based on this factor, the ALC-CFAR tailors the background estimation algorithm. The conducted Monte Carlo simulation results demonstrate that the proposed detector provides low loss CFAR performance in an homogeneous environment and also performs robustly in presence of interfering targets. The performances of the ALC-CFAR detector have been evaluated and compared with that of the CA-CFAR and the OS-CFAR detectors. The obtained results are presented and discussed in this paper.

A study of the raindrop size distribution along the eastern coast of South Africa (Durban) is presented. The Biweight kernel estimator based on distometer measurement is used to determine the best estimate of the measured raindrop size probability distribution function (pdf). The best kernel estimator, which results in the lowest integral square error (ISE), is used to measure the closeness of the estimated lognormal and gamma pdf of raindrop size to the measured raindrop size distribution. It is established that the optimised lognormal pdf slightly outperforms the optimised gamma pdf in terms of the mean ISE and the RMSE values, with mean ISE values of 0.026 for lognormal and 0.04 for gamma distributions, respectively, and corresponding mean RMSE values of 0.073 and 0.081, respectively. The method-of-moments gamma and lognormal distributions are observed to be worse estimators of the measured pdf than the two optimized distributions. The N(D) distributions using the optimised l gnormal and gamma distributions for the region are compared with those for different tropical regions, namely, India, Singapore, Nigeria, Indonesia, and Brazil. While the Indian lognormal N(D) model gives the highest peak for low raindrop sizes for all rain rates, Durban's gamma and lognormal models exhibit the widest raindrop size spread over all rain rates ranging from 1-120 mm/h. Finally, the specific attenuation due to rain using the Durban models are compared against the ITU-R models and actual measurements over a 19.5 GHz LOS link; the results indicate a need for further work involving both distrometer and radio link measurements for rain rates exceeding 30 mm/h in the eastern coast of South Africa.