As an important signature of the radar target, the angular glints effects on radar sensor mainly arise at close distance, especially at target near field. However, the current prediction methods of angular glint are mostly based on the far field condition. This paper presents a prediction technique of near field angular glint based on the scattering center model to solve this problem. Firstly, the near field backscattering is represented based on far-field scattering center model. Then by solving the derivative of the backscattering phase vs. the position vector of the observer, including incident angles and range, we get the exact expression of angular glint at near field. Next, the exact expression is approximated and simplified in the range of terminal guidance. Finally, the factors affecting near-field angular glint are analyzed using numeric simulation, and the error comparison between the exact and approximate expression is also provided. It is concluded that the expression in [1] is the approximation of ours at far field under certain polarization, and the simplified expression has a well precision in the range of terminal guidance. All these results provide the theoretical basis for the prediction of near field angular glint and its signature research.

A free-space, non-destructive method for measuring the complex permittivity of a double-layer bulk dielectrics and thin film oxide layers at microwave frequencies have been developed. The method utilizes a spot-focusing antenna system in conjunction with a vector network analyzer in the range of 18-26 GHz. The bulk dielectric was measured using the Transmission Method and Metal-Backed Method, while the Metal-Backed Method was used to investigate the thin films. Both types of samples were sandwiched between two quarter-wavelength Teflon plates to improve the mismatch at the frequencies of measurement. The thin film sample arrangement was backed by an additional metal plate. The double-layer bulk dielectric samples were Teflon-PVC and Plexiglas-PVC, while the thin film samples consisted of SiO₂ layers of different thicknesses grown on doped and undoped Si wafer substrates. The relative permittivity obtained for PVC ranged between 2.62 to 2.93, while those for Plexiglas exhibited values between 2.45 to 2.63. The relative permittivity of SiO₂ deposited on these wafers was between 3.5 to 4.5. All these values were in good agreement with published data The advantage of the method was its ability to measure the dielectric properties of the films at the mid-frequency band irrespective of the substrate type used. Simulations of the measurement setup were carried out using CST Microwave Studio and the simulation results agreed closely with the measurements.

In this paper a printed regular hexagonal slot antenna with a hexagonal stub fed by a coplanar waveguide line has been considered for ultra wide bandwidth. This antenna is then modified to obtain dual band rejection. The Wireless Local Area Network (WLAN) and Wireless Microwave Access (WiMAX) band rejections are realized by incorporating a C-shape slot within the exciting stub as well as a couple of Z-shape open circuit stubs symmetrically inserted at the edge of the slot. The length and width of the C-shape slot and Z-shape stub offer sufficient freedom for selecting and shifting the notch bands. Magnitude of S11, impedance, gain and radiation characteristics of them are studied and discussed here. From the measured results, it has been observed that the impedance bandwidth, defined by magnitude of S11 ≤ -10 dB, reaches a value of 8.18 GHz (2.96~11.14 GHz) except dual frequency stop bands of 3.28-3.7 GHz and 5.1-5.90 GHz. From the experimental results, it is observed that the radiation patterns are omnidirectional in the H-plane and dipole in nature in the E-plane. The antenna gain varies from 4.8 dB to 5.3 dB over the whole operating band excluding the notch bands. Surface current distributions are used to analyze the effects of the C-slot and Z-shape stub. Measured group delay has very small variation within the operating band except notch bands and hence the proposed antenna may be suitable for UWB applications.

The knowledge of amplitude and location of sliding scattering centers is necessary for low detectable streamlined targets in many applications, such as precise estimation of shape or velocity of targets, and also target tracking and recognition. Based on the thorough analysis of scattering characteristics, the scattering center features of streamlined targets are presented which demonstrate the dependence of location and amplitude on the target orientation relative to the radar. Then based on these features, an accurate scattering center model for streamlined targets is proposed. The parameters of this model is estimated by genetic algorithm, and then the given model with estimated parameters is validated by full wave numerical method allowing precise backscattered data computation.

In this paper, applications of the discrete Green's function (DGF) in the three-dimensional (3-D) finite-difference time-domain (FDTD) method are presented. The FDTD method on disjoint domains was developed employing DGF to couple the subdomains as well as to compute the electromagnetic field outside these subdomains. Hence, source and scatterer are simulated in separate subdomains and updating of vacuum cells, being of little interest from a user point of view, can be avoided. In the developed method, the field radiated by a single subdomain is computed as a convolution of DGF with equivalent current sources measured over two displaced Huygens surfaces. Therefore, the computed electromagnetic field is compatible with the FDTD grid and can be applied as an incident wave in a coupled total-field/scattered-field (TFSF) subdomain. In the developed method, the DGF waveforms are truncated using the Hann's window and windowing parameters assuring accuracy of computations are pointed out. The error of the field computations varies between -90 dB and -40 dB depending on the DGF length and excitation waveform. However, if the DGF length is equal to the number of iterations in a simulation, the presented DGF applications return the same results as the direct FDTD method.

Due to the increased use of indoor wireless networks and the concern about human exposure to radio-frequency sources, exposure awareness has increased during recent years. However, current-day network planners rarely take into account electricfield strengths when designing networks. Therefore in this paper, a heuristic indoor network planner for exposure calculation and optimization of wireless networks is developed, jointly optimizing coverage and exposure, for homogeneous or heterogeneous networks. The implemented exposure models are validated by simulations and measurements. As a first novel optimization feature, networks are designed that do not exceed a user-defined electric-field strength value in the building. The influence of the maximally allowed field strength, based on norms in different countries, and the assumed minimal separation between the access point and the human are investigated for a typical office building. As a second feature, a novel heuristic exposure minimization algorithm is presented and applied to a wireless homogeneous WiFi and a heterogeneous WiFi-LTE femtocell network, using a new metric that is simple but accurate. Field strength reductions of a factor 3 to 6 compared to traditional network deployments are achieved and a more homogeneous distribution of the observed field values on the building floor is obtained. Also, the influence of the throughput requirement on the field strength distribution on the building floor is assessed. Moreover, it is shown that exposure minimization is more effective for high than for low throughput requirements and that high field values are more reduced than low field values.

Based on the Propagation-Inside-Layer Expansion (PILE) and the Forward-Backward method (FBM), the composite scattering from the target below a dielectric rough soil surface using the extended PILE (EPILE) combined with the Forward-Backward method (FBM) is studied. The accuracy and efficiency of the EPILE+FBM for this specific type of composite scattering is researched by comparing with the method of moments (MOM), the influences of the target size, target depth, target horizontal distance, the rms height, the correlation length, the incident angle and the soil moisture content, etc, to the bistatic scattering coefficient (BSC) are also investigated.

A wideband resonant antenna loaded with coplanar waveguide (CPW) epsilon negative transmission metamaterial line (ENG MTL) unit cells is proposed. The CPW geometry provides high design freedom, and the metamaterial resonant antenna is designed on a CPW single layer where vias are not required. The novel ENG unit cell on a vialess single layer simplifies the fabrication process. The dispersion analysis of the metamaterial unit cell reveals that increasing right hand capacitance and left hand inductance can decrease the half-wavelength resonance frequency, thus reducing the electrical size of the proposed antenna. Based on the proposed ENG MTL unit cell the wideband antenna is verified by a commercial EM simulator HFSS11 and developed. Comparing the measured performances with those resonant antennas, it is noticed that the proposed antenna achieves high bandwidth and further size reduction, higher efficiency and easier manufacturing. The realized antenna has a compact size of 0.32λ₀ × 0.20λ₀ × 0.012λ₀ (26.6 mm × 16.8 mm × 1 mm) at 3.65 GHz, and operates over the frequency ranges 3.38-4.23 GHz suitable for WiMAX applications. Good agreement between the simulated and measured results is obtained.

A novel compact single-feed circularly-polarized (CP) microstrip patch antenna is proposed for CNSS dual-band application. The antenna comprises a square patch with embedded four symmetrical C-slots parallel to the edges and a slit in the center. The dual resonance frequencies (1616 MHz and 2492 MHz) can be separately controlled by the square patch and the C-slots. The CP characteristics is mainly achieved by adjusting the slit length. The antenna has a low profile and a small size. Details of design and results for the proposed antenna are presented and discussed.

In this paper, a novel four-port symmetric coupled composite right-/left-handed (CRLH) transmission line in common-/differential-mode operation is introduced. The symmetric metamaterial structure is based on a unit-cell which under a differential-mode excitation behaves like a CRLH metamaterial with bandpass filter characteristics. In contrast, the CRLH metamaterial is below the cut-off frequency under a common-mode excitation. To validate these features, a five-cell four-port symmetric CRLH-TL is simulated, fabricated, and measured, and the obtained results verify the bandpass filter features of the structure under differential-mode excitation.

The insertion loss of different materials is measured at 2.4, 3.3 and 5.5 GHz bands. Directive antennas with a nominal gain of 19 dB are used in the measurement campaign. The height of the antennas has been selected to have the minimum possible reflection from around surfaces. Thick concrete wall, thick concrete column and tree's insertion loss are measured. It is noticed that the insertion loss increases with the increment of the operating frequency. For tress, the insertion loss for the leafless tress is 6 to 10 dB lower than the deciduous trees.

The hybrid finite element-boundary integral-multilevel fast multipole algorithm (FE-BI-MLFMA) is a powerful method for calculating scattering by inhomogeneous objects. However, the conventional FE-BI-MLFMA often suffers from iterative convergence problems. A non-overlapping domain decomposition method (DDM) is applied to FE-BI-MLFMA to speed up the iterative convergence. Furthermore, a preconditioner based on absorbing boundary condition and symmetric successive over relaxation (ABC-SSOR) is constructed to further accelerate convergence of the DDM-FE-BI-MLFMA. Numerical experiments demonstrate the efficiency of the proposed preconditioned DDM-FE-BI-MLFMA.

A novel multi-state RF MEMS switch for microstrip antenna applications is presented. The proposed switch exhibits seven different states of operation, has a very simple DC biasing mechanism and can be integrated with antenna structure. Based on these properties, this switch may find its usage in multifunction reconfigurable antennas. To exhibit this application, it is employed in the reconfiguration mechanism of a U-slotted antenna. In different states of the switch, the antenna resonates at different frequencies. All the standard frequency bands of the wireless communication services with some additional frequency bands is covered with this reconfigurable U-slotted antenna. Moreover, the proposed antenna structure is a cost-effective solution since it comprises a commonly used FR4 substrate. The switch is integrated with antenna structure on the same substrate. A prototype of the designed antenna was fabricated and tested for performance verification of the proposed switch and antenna.

The range profile (RP) of an automobile is derived by compressing the wideband radar signal, and it can be utilized for the classification and thus contribute to lane change and collision avoidance. However, the limited radar bandwidth due to the cost and the system complexity impedes the successful classification. This paper proposes an efficient method to construct an efficient feature vector of the automobile RP through combined use of the central moment, the information on the maximum-minimum and the peak information. Simulation results using the five automobile models composed of point scatterers and a simple nearest neighbor classifier prove that the proposed method improves the classification result, especially in the multi-aspect classification.

This paper proposes a coupling model of the Quasi-Continuous High Magnetic Field (QCHMF) systems that incorporates the electrical, thermal and mechanical dynamics of the magnet system and the power supply system. The design of QCHMF systems is formulated as a five-objective optimization problem and a scoring system based on preference of the designer is adopted to classify the Pareto points of the optimization problem. An optimized mono-coil 50 T/100 ms QCHMF system is designed with a 67.5 MW rectifier of the Wuhan National High Magnetic Field Center (WHMFC), which is taken as an example to verify the proposed model and optimization method. Detailed simulation models of the optimized QCHMF system are built in Matlab and Comsol and the results agree well with the designed technical specifications. The proposed model and optimization method are generic which can be applied to other QCHMF systems with minor modifications.

When using ultra-wide band (UWB) radar to detect targets in various conditions, identifying whether the target buried under building debris or in bad visibility conditions is a human or an animal is crucial. This paper presents the application of the wavelet entropy (WE) method to distinguish between humans and animal targets through brick wall and in free space at a certain distance. In the study, WE, WE change, and WE of the related range points were estimated for the echo signals from five humans and five dogs. Our findings indicate that the entropy or degree of disorder in the energy distribution of the human target was much lower than that of the dog, and the waveform of the human's entropy was smoother than that of the dog. In addition, the body micro motions of humans are much more ordered than those of dogs. WE can be employed as a quantitative measure for recognizing invisible targets and may be a useful tool in the UWB radar's practical applications.

This paper analyzes the azimuth spectrum folding problem which arises from the dependence of the Doppler centroid on range frequency in squinted spotlight synthetic aperture radar (SAR). Based on the analysis, a novel approach for squinted spotlight SAR is proposed in this paper. In this approach, an azimuth preprocessing step including a deramping operation and an operation of azimuth spectrum replicating and filtering is introduced to eliminate spectrum folding problem. Then, a modified Range Migration Algorithm (RMA) is adopted to process the preprocessed data. This approach extends the focusing capacity of traditional two-step processing approach from broadside spotlight SAR to squinted case. Moreover, this approach is e±cient due to a limited azimuth data extension to resolve the spectrum aliasing problem. Experimental results on simulated raw data validate the proposed approach.

A novel compact microstrip-fed planar monopole antenna with quad-notched bands is presented. The proposed antenna is based on one rectangular-stepped-patch. To achieve the higher resonance over the 12 GHz, one lateral L-shaped structure is embedded in the ground. By inserting four U-shaped slots in the radiation patch, quad band-notched properties in the WiMAX (3.3-3.6 GHz), INSAT(4.5-4.8 GHz), lower WLAN (5.15-5.35 GHz) and higher WLAN (5.725-5.825 GHz) are obtained. Experimental results indicate that the designed UWB antenna can obtain broadband matched impedance values, good frequency selectivity over the notched bands, relatively flat group delay and nearly omni-directional transmission characteristics across the UWB frequencies. More importantly, the quad-notched bands can be reconfigurable by shorting the corresponding U-shaped slots.

An analysis method for electromagnetic field coupling to microstrip line connected with nonlinear components is proposed in this paper. Different from the published work, not only the voltage and current response of the nonlinear component connected to the transmission line (TL) can be obtained, but also the power transmitted from this nonlinear component to the next one at both the fundamental frequency and harmonics can be predicted. The proposed method suitably combines the classical field-to-TL coupling theory and the nonlinear large-signal scattering parameters on the basis of a black box model in frequency-domain. Then this method is experimentally validated by a laboratory system including a microstrip line connected with a simple nonlinear component constituted by the anti-paralleled HSMS-282C Schottky diodes pair welded to a 50 Ω microstrip line. The calculated results using the proposed method show good agreement with the measured data.

Directional and switched-beam antennas in wireless sensor networks are becoming increasingly appealing due to the possibility to reduce transmission power and consequently extend sensor node lifetime. In this work a reconfigurable beam-steering antenna is proposed for Wireless Sensor Network applications in the ISM band (f=2.4-2.4835 GHz). The proposed radiating structure consists of a vertical half-wave dipole antenna and eight microstrip antennas composed of a rectangular two-element patch antenna array. These microstrip antennas have a directional radiation pattern in the azimuth plane with a HPBW of nearly 60 degrees. A control circuit consisting of a transmission line, RF-switches and a 4:16 multiplexer has been designed in order to dynamically switch among nine radiation patterns, eight directional and one omnidirectional. Simulations and experimental results, referred to a low-cost realization on a FR4 substrate with a thickness of 1.6 mm, demonstrate appreciable performance.