Ramp response technique in low frequency can be used for generating 3-dimensional images of radar targets (even stealthy or buried targets) so as to identify them. This technique uses the target profile function, which is defined as its transverse cross- sectional area versus distance along the observing direction. For mutually orthogonal observing views, reconstructed 3D images are quite accurate. However, in practice, due to the bias introduced from the response in shadow region and from limited non-orthogonal observing directions, reconstructions become distorted.To evaluate the quality of the reconstruction and to further identify objects from their reconstruction, we need to calculate profile functions of 3D reconstructed objects in arbitrary directions. Therefore, in this paper, we propose an algorithm meeting this needs.

In this paper, a novel second-order transmission condition is developed in the framework of non-conformal finite element domain decomposition method to meet the challenges brought by complex and large-scale electromagnetic modeling. First, it is implemented efficiently on the non-conformal interface via a Gauss integral scheme. Then, the eigenvalue analysis of the DDM system show a more clustered eigenvalue distribution of this transmission condition compared with several existing transmission conditions. After that, it is applied to large-scale complex problems such as S-type waveguides in the high frequency band and dielectric well-logging applications in the low frequency band. The final numerical results demonstrate that this transmission condition has high efficiency and huge capability for modeling large-scale problems with multi-resolution in any frequency band.

In this paper, two staggered array configurations are presented for enhancing size and radiation properties of wideband phased array systems. The proposed arrays are obtained either by rotating each element 45° or by inserting additional rows in the middle which are shifted by half the distance between elements. These two configurations allow for a smaller distance between array elements (29% less), while the actual distance between elements in the diagonal direction is kept the same. Reducing the distance between elements results in eliminating/reducing the grating lobes in a wider frequency range, which improves the array usable bandwidth. In addition, this proposed array produces better gain and maximum steering angle.

This paper addresses the possibility of displacement measurement by microwave interferometry at an unknown reflection coefficient with the use of as few as two probes. The case of an arbitrary interpobe distance is considered. The measurement error as a function of the interprobe distance is analyzed with the inclusion of variations of the detector currents from their theoretical values. The analysis has shown that as the interprobe distance decreases, the maximum measurement error passes through a minimum for reflection coefficients close to unity and increases monotonically for smaller reflection coefficients. Based on the results of the analysis, the interprobe distance is suggested to be one tenth of the guided operating wavelength λ_g. In comparison with the conventional interprobe distance of λ_g/8, the suggested one offers a marked reduction in the maximum measurement error for reflection coefficients close to unity, while for smaller ones this error remains much the same (for a detector current error of 3%, the maximum measurement error in percent of the operating wavelength is 2.2% and 1.0% at λ_g/10 as against 4.8% and 2.7% at λ_g/8 for a reflection coefficient of 1 and 0.9, respectively, and 2.9% at λ_g/10 as against 2.4% at λ_g/8 for a reflection coefficient of 0.1).

The fine-grained parallel micro-genetic algorithm (FGPMGA) is developed to solve antenna design problems. The synthesis of uniformly exited unequally spaced array is presented. Comparison with the micro-genetic algorithm (MGA) has been carried out. It is seen that the FGPMGA significantly outperforms MGA, in terms of both the convergence rate and exploration ability. The FGPMGA can also reduce the optimization time. Then the FGPMGA and the body of revolution finite-difference time-domain (BOR-FDTD) are combined to achieve an automated design process for conical corrugated-horn antenna. Numerical simulation results show that the horn antenna has good impedance matching (the VSWR is less than 1.5), stable beamwidth and gain, as well as good rotation symmetry patterns over the whole band 8~13 GHz.

A compact quad-band hybrid antenna for Compass/WiMAX/WLAN applications is proposed. The hybrid antenna is designed based on the method of combining a composite right/left-handed transmission line (CRLH-TL) unit cell with a meandered monopole and wide multi-band characteristics are achieved by merging some of resonance frequencies of the CRLH-TL unit cell and meandered monopole together. Coplanar waveguide (CPW) is used as a parallel excitation for both the CRLH-TL unit cell and meandered monopole. A prototype of the proposed hybrid antenna has been constructed and experimentally studied. The measured results show that four distinct operating bandwidths with 10 dB return loss are about 30 MHz (1.25-1.28 GHz), 290 MHz (2.44-2.73 GHz), 650 MHz (3.17-3.82 GHz) and 1130 MHz (5.03-6.16 GHz), covering the Compass B3, 2.5/3.5/5.5 GHz WiMAX and 5.2/5.8 GHz WLAN bands. Furthermore, the antenna has a single-layer planar structure with a small volume of only 31 × 21 × 2 mm³. Acceptable radiation patterns and peak realized gains are obtained over the operating bands.

In this paper, we present a low-profile, compact, ultra-wideband antenna that uses a set of closely coupled radiators. The system of two coupled radiators has two different linearly independent modes of operation with complementary frequency bands of operation. These include the differential mode and the common mode of operation. When the antenna is excited in the common mode of operation, it acts as an ultra-wideband (UWB) antenna covering a broad frequency band. When excited in the differential mode, the antenna operates as a wideband dipole in a frequency range below that of the common mode. Thus, by appropriately combining the two modes using a suitably designed feed network, the bandwidth of the antenna can be extended and its lowest frequency of operation is reduced. Mode combining is achieved with a feed network that employs a frequency-dependent phase shifter. Using this feed network, the two modes of the antenna are combined and a single-port broadband device is achieved that has a bandwidth larger than that of either the common or the differential mode individually. A prototype of the antenna is fabricated and experimentally characterized.

In this paper, the design of an array of wideband combined antenna elements is presented. A TEM horn antenna is combined with magnetic dipoles to obtain a wideband element with a bandwidth from 180 MHz to 30 GHz. The element is then miniaturized in order to be placed in a two by two array, and then the optimized values of the horizontal and vertical spacings are calculated. To enhance the array bandwidth, a lens is placed in front of each element. This leads to an increase in the bandwidth from 0.2 to 10 GHz while no grating lobes appear over the bandwidth. The combined element is fabricated and the simulation results are verified by the measured data. Furthermore, simulation results for the return loss, radiation patterns and antenna gain for the 2 × 2 array are presented.

Spherical shells are proposed and presented to improve the gain of a class of wideband phased array systems. This kind of phased arrays is composed of compact elements, which allow for a small distance between elements that is much less than half wavelength at lower operating frequencies. This small distance, as a function of wavelength, results in a small gain. Therefore, shells confronting the array are proposed to improve the gain. The formulations required to define the geometry and material properties of the shell are developed. Two and four element arrays are designed and simulated with and without shells to test the technique, and promising results are obtained at lower frequencies for the array with shells.

In this paper, an experimental characterization of a MIMO underground channel is presented. A simple statistical model is proposed at 2.45 GHz. The Channel is characterized in terms of path loss, shadowing, RMS delay spread, and capacity. The measurements are carried out in an underground mine, which is a harsh confined environment. The path loss model is extracted from measured data for the line of sight (LOS) and non line of sight (NLOS) scenarios for both MIMO and SISO channels. The path loss exponent in LOS is less than 2 in MIMO and SISO as the environment has a dense concentration of scatterers. A statistical study is carried out to find the delay spread. For MIMO and SISO, there is no relation between the delay spread and the transmitter receiver distance. Furthermore, the delay spread of the MIMO is less than the one of the SISO channel in the LOS measurement campaigns. Aikake information Criteria are used as a goodness of fit for different statistical distributions to represent the delay spread. According to the calculated capacity for a constant signal to noise ratio in LOS case, the transmission performance is significantly improved by using the MIMO scheme over the traditional SISO. Therefore, MIMO is an ideal candidate for future wireless underground communications.

This paper is concerned with the theory of wave propagation in biaxial anisotropic media. Consider a multilayered planar structure composed of media with electric and magnetic anisotropy, surrounded by two half spaces. Exat relations for reflection coefficient from this structure can be useful for arriving at the intended applications. In this paper, by matching of transverse field components at the bounderies, we will arrive at exact recursive relations for reflection coefficient of the structure. In the previous works, the magnetic and electric anisotropy were not taken into consideration at the same time, or complex relations were arrived. But using this novel method, those complexities will not appear and both electric and magnetic anisotropy are take into consideration. Moreover, we will not set any limits on the right half-space so the right most half-space may be a PEC, PMC, PEMC, surface impedance, dielectric or a metamaterial. Finally, the last section of the paper confirms the validity of the relations arrived at and as an interesting application; the zero reflection condition will be obtained.

A WLAN band notched compact ultra-wideband (UWB) microstrip monopole antenna with stepped geometry is proposed. A L-slot loaded modified mushroom type Electromagnetic Band Gap (EBG) is designed, analyzed and used to realize notched band characteristics for wireless local area network (WLAN) in the UWB frequency range. The proposed antenna having partial ground plane is fabricated on a low cost FR4 substrate having dimensions 40 ( Lsub ) × 30 (Wsub ) × 1.6 (h) mm³ and is fed by a 50-Ω microstrip line. The results show that the proposed antenna achieves impedance bandwidth (VSWR < 2) from 2.3 GHz to 11.4 GHz with band notched characteristics (VSWR > 2) from 4.9 GHz to 6 GHz. Fidelity factor for proposed antenna is also analyzed to characterize time domain behavior. Simulation and measurement results of VSWR are found in good agreement.

A miniaturized crossed-dipole fractal antenna with circular polarization is presented in this letter. The radiating elements of the antenna were built as the Koch curve, and the antenna was mounted on a specially designed ground plane. Furthermore, the influence of fractal dimension to bandwidth and axial ratio of fractal antenna is also experimentally studied. The bandwidth of the VSWR≤ 1.5:1 within 3dB axial ratio for the fractal antenna is about 5.98%. The measured results show that the proposed fractal antennas have good circular polarization property, efficiency and 23.4-33.5% size reduction comparing with the conventional crossed-dipole antenna. The tested results are in good agreement with that of the simulations.

This paper describes how information about the electromagnetic structure of targets can be obtained from direct detection radar techniques, where the relative phase of the transmitted and received signals is not measured. A comparison is made between the resolved structure of a simple test target from an ultra wide band, pulse synthesis direct detection radar system at 14-40 GHz and an equivalent heterodyne radar receiver where phase information is recorded. The test targets employed are wax sheet of thickness 20 mm and 80 mm which are illuminated alone and in contact with the human body. A vector network analyser is used as the radar system. The simplicity of constructing ultra wide band direct detection radar systems combined with their cost makes the use of such radar systems appealing for applications such as concealed threat detection and nondestructive testing, where absolute range to the target, if required, can be determined by other methods.

This paper proposes miniature radio frequency identification (RFID) tag antenna designed to operate on metallic objects, in the UHF frequency range (915 MHz), without significantly degrading its read range. The antenna structure is composed of two parts: Part 1 comprises two square patches electrically connected to the ground plane through vias while Part 2 is an unconnected inter-layer consisting of two square complementary split ring resonators to allow for capacitive reactance increase. Consequently, its self-resonant frequency will shift towards low frequency, which theoretically allows shrinking RFID tag antenna into smaller size. The antenna was simulated and measured to verify its conjugate matching with chip impedance. The results of experimental tests show that the proposed RFID tag offers a maximum read range of 0.82 m when placed on a metallic object. The tag's overall size is 36.7×18.1×3.2 mm³. Both simulation and measurement results are provided to validate the design.

Two improved circularly polarized microstrip planar antennas operating in 5 GHz-6 GHz are proposed in this paper. The Swastika slot and a circular feeding line are introduced into Ant.2 which exhibits wide impedance bandwidth and AR bandwidth during simulation and measurement than a basic truncated edge CP microstrip antenna. In further studies, a center circular slot is introduced into Ant.3, and the experimental results show a wider impedance bandwidth and AR bandwidth with high gain.

A miniaturized triple-band branch-line coupler based on the simplified dual-composite right/left-handed transmission line (S-D-CRLH-TL) is proposed in this paper. The electromagnetic characteristics of S-D-CRLH-TL are analyzed by the simulator and equivalent circuit model, and the results prove that there are three frequencies with phase of -90° in the passbands; this characteristic can be applied in designing triple-band quadrature microwave components. The proposed branch-line coupler is fabricated and measured, the measured and simulated results are in good agreement with each other, showing that the triple-band operating at 3.06 GHz, 4.00 GHz and 5.54 GHz, the useful bandwidths are 2.97 GHz-3.16 GHz, 3.82 GHz-4.12 GHz and 5.48 GHz-5.67 GHz. In addition, compared with the conventional branch-line coupler, the whole size of the proposed one is 17 mm × 14.4 mm (0.173λ × 0.147λ) (λ is the wavelength in low frequency), it realizes a 73% size reduction. Moreover, compared with the triple-band branch-line coupler based on the double-Lorentz transmission line metamaterial, the proposed branch-line coupler is more effective in the situation, which is sensitive to phase-changing, as the sign of phase difference in the two outputs at the three frequency points keeps the same.

Ultra wide band (UWB) impulse radio (IR) technology has different applications in different sectors such as short range radios and collision avoidance radar. A strong signal denoising method is needed for UWB-IR signal detection. One of the challenges of UWB-IR signal detection technique is the environmental interferences and noises. Wavelet Packet Transform (WPT) based multi-resolution analysis technique is suitable for this kind of signal denoising and detection. The paper describes a better method of denoising and detection technique of UWB-IR signal based on calculation of energies of the coefficients of each WPT terminal-node and by using an improved threshold calculation technique. The proposed technique is investigated through both simulation and experimentation.

The uniform expressions of scalar fringe waves which are based on the physical theory of diffraction (PTD) were obtained for the impedance half plane in terms of the Fresnel integrals. Asymptotic and uniform forms of the fringe fields were compared. The radiated fields of the fringe expressions were analyzed numerically.

This paper proposes an Extended Inverse Chirp-Z Transform (EICZT) algorithm to handle the high squint FMCW SAR data, where the conventional Inverse Chirp-Z Transform (ICZT) cannot work due to the failure in dealing with the range-variance of second- and higher-order range-azimuth coupling terms. A pre-processing operation is implemented in the azimuth-Doppler and range-time (Doppler-time) domain, where a perturbation function consisting of second-order and third-order range time variables is implemented to compensate the range variance of the second order range terms. Moreover, a new scaling factor is formulated to represent the Range Cell Migration (RCM), and further corrected by the presented EICZT approach. The proposed approach is analyzed and compared with the conventional ICZT. The simulated high squint SAR scene with nine targets is well focused by the proposed approach and the quality is greatly improved with respect the conventional ICZT. The proposed algorithm is also validated by the X-band high-resolution real SAR data.