Diamond dipole antennas with textile Artificial Magnetic Conductor (AMC) sheet-like waveguide were designed to investigate the possibility of improving transmission between antennas. Fleece fabric is used as the substrate of the textile AMC while SHIELDIT fabric is used as the conductive patches and ground plane. The AMC surface is designed to resonate at 2.45 GHz with the goal to enhance the transmission between antennas. A small textile AMC waveguide sheet as well as an AMC waveguide jacket were fabricated. The S-parameters performance of the two antennas with textile AMC sheet was investigated in a free space environment and near to human body setting. The effect of different antennas' orientations was also considered. Measurements were conducted thoroughly to validate the simulated findings. Compared to free space environment, S₂₁ transmission between two dipoles is improved up to maximum -10 dB when having textile AMC waveguide sheet beneath them. For both off-body and on-body placements, significant transmission enhancement has been observed with the introduction of the AMC sheet-like waveguide. Directive radiation patterns with high gain have also been achieved with the proposed AMC waveguide jacket.

It is shown that metal gratings can be used to improve the cross polarization of circularly-polarized aperture-coupled microstrip antennas. The metal gratings reduce edge diffraction from the finite-size grounded dielectric slab on which the antennas are printed. The edge diffraction is due to surface waves that can propagate in the grounded dielectric slab. The design of the metal grating is based on an analytical model, which results in a first-order estimation for the design of the metal grating structure. The model provides physical insight and appears to be accurate enough for the application. Using this model, a prototype was developed, consisting of a circularly-polarized 2×2 microstrip array with associated feeding network. Measurements show that the axial ratio can be reduced down to 1.75 dB within the beam width of the antenna.

In this letter, a novel microstrip-fed monopole ultrawideband (UWB) antenna with triple notched band is proposed. By embedding a novel modified capacitively loaded loop (CLL) resonator beside the microstrip feed line, band-rejected filtering properties in 3.3-3.6 GHz for WiMAX, 5.15-5.825 GHz for WLAN, and 7.25-8.295 GHz for the X-band satellite is generated. The notched frequencies can be adjusted according to specification by altering the parameters of the modified CLL resonator. Both the experimental and simulated results of the proposed antenna are presented, indicating that the antenna is a good candidate for various UWB applications.

An analytical procedure for the calculation of the inductance of planar zig-zag spiral inductors is proposed. The procedure is based on the partial inductance concept and models the inductor as a series of a number of parts. The self-inductance of each individual part, which has the shape of a parallelogram, and the mutual inductance between any two parts of the inductor are determined. The inductance of a planar zig-zag spiral inductor can thus be obtained for any width, length and angle of the saw-tooth configuration. The procedure is validated with experimental measurements; the agreement between estimated and measured inductances is very good.

In this article, a novel compact reconfigurable antenna based on substrate integrated waveguide (SIW) technology is introduced. The geometry of the proposed antennas is symmetric with respect to the horizontal center line. The electrical shape of the antenna is composed of double H-plane SIW based horn antennas and radio frequency micro electro mechanical system (RF-MEMS) actuators. The RF-MEMS actuators are integrated in the planar structure of the antenna for reconfiguring the radiation pattern by adding nulls to the pattern. The proper activation/deactivation of the switches alters the modes distributed in the structure and changes the radiation pattern. When different combinations of switches are on or off, the radiation patterns have 2, 4, 6, 8,... nulls with nearly similar operating frequencies. The attained peak gain of the proposed antenna is higher than 5 dB at any point on the far field radiation pattern except at the null positions. The design procedure and closed form formulation are provided for analytical determination of the antenna parameters. Moreover, the designed antenna with an overall dimensions of only 63:6 ×50 mm² is fabricated and excited through standard SMA connector and compared with the simulated results. The measured results show that the antenna can clearly alters its beams using the switching components. The proposed antenna retains advantages of low cost, low cross-polarized radiation, and easy integration configuration.

We advance the theory of the two-dimensional method of connected local fields (CLF) to the three-dimensional cases. CLF is suitable for obtaining semi-analytical solutions of Helmholtz equation. The fundamental building block (cell) of the 3-D CLF is a cube consisting of a central point and twenty six points on the cube's surface. These surface points form three symmetry groups: six on the planar faces, twelve on the edges, and eight on the vertices (corners). The local field within the unit cell is expanded in a truncated spherical Fourier-Bessel series. From this representation we develop a closed-form, 3-D local field expansion (LFE) coefficients that relate the central point to its immediate neighbors. We also compute the CLF-based FD-FD numerical solutions of the 3D Green's function in free space. Compared with the analytic solution, we found that even at a low three points per wavelength spatial sampling, the accumulated phase errors of the CLF 3D Green's function after propagating a distance of ten wavelengths are well under ten percent.

The specific features of TM-polarized surface electromagnetic waves in a finite structure fabricated by a periodic alternating semiconductor and dielectric layers are investigated. Dispersion characteristics of eigenwaves are analyzed numerically and analytically. The complex Poynting energy flux and the surface wave's distribution are calculated. The influence of geometrical and physical parameters of the structure on the properties of surface waves is studied.

Multifractal correlation, which studies the spatial correlation characteristics of two points with different singularity indexes, is a generalization of multifractal single point statistic. This paper introduces multifractal correlation theory into the characteristic analysis of aircraft echoes from low-resolution surveillance radars, and discusses the application of multifractal correlation characteristics in target classification. Firstly, on basis of introducing multifractal correlation theory, the multifractal correlation characteristics of aircraft echoes from surveillance radars are analyzed in detail by means of the multifractal correlation analysis. Secondly, on basis of the foregoing analysis, several characteristic parameters of the echo multifractal correlation spectrum are defined, and the support vector machine (SVM) based on the defined characteristic parameters is taken as the classifier to classify different types of aircraft targets. Finally, real recorded aircraft echo data are adopted to do the classification experiments, and the experimental results validate the proposed method.

A robust direct data domain least squares (D3LS) beamforming algorithm that is capable of reducing the sidelobe level of the beam pattern is presented. By exploiting the sparsity of the desired beam pattern, the proposed method can enhance the performance with its lower sidelobe level and deeper null for interference while the robustness against steering vector mismatch is increased when a proper regularization parameter is selected. Simulation results demonstrate the effectiveness of the proposed method.

Based on a construction of concentric deformed annular slots with a stepped microstrip feed line, two designs of dual-band dual-sense circularly polarized slot antenna are proposed in this paper. Compared with the first antenna, the second design possesses the merits of simple structure by devising a twin-slot with less adjusted parameters to achieve the same satisfactory output responses. The results from simulations and measurements demonstrate that both of the antennas have good quality of impedance matching and dual-sense circular polarization at 1.6 GHz and 2.5 GHz.

Measurements of mm-wave excitation spectra of high-order whispering gallery modes in free-space cylindrical disk resonators as functions of resonator thickness have been made. Resonators in the form of tight stacks of thin dielectric disks excited via dielectric waveguides have been used in the experiment. Experimental conditions for the excitation of thin-disk resonators have been found. A simple approach for the modeling of resonator spectra and recovery of dielectric parameters has been proposed.

In this paper, 60 GHz millimeter-wave indoor propagation characteristics are simulated and analyzed using the method of SBR/IM (shooting and bounding ray tracing/ image). And the simulated and measured results agree well, so the correctness of the method has been validated. Some propagation parameters are obtained in the simulation, such as the indoor reception power distribution, distribution of phase angle of received power, root mean square (RMS) delay spread, direction of arrival, RMS angular spread, Doppler shift, etc. The analysis of the above results provides the foundation for the indoor coverage of millimeter-wave communication system.

The Medium-Earth-Orbit SAR（MEOSAR）is one of the potential next-generation spacebarne SAR for its excellent performance, however, due to ionospheric effects, a MEOSAR may not be able to produce data useful for science applications. So study of ionospheric effects is one of the critical techniques for the development of MEOSAR. In this paper, we present ionospheric effects on azimuth imaging for MEOSAR. First, we establish an analysis model for ionospheric effects on azimuth imaging of MEOSAR based on the system characteristics of MEOSAR and the temporal-variability of ionosphere. Then, based on the analysis model, we analyze the effects caused by the quadratic and cubic phase errors induced by temporal-variability of ionosphere on azimuth imaging. According to the results of our analysis, we conclude that both the quadratic phase error and the cubic phase error neglected for Low-Earth-Orbit SAR(LEOSAR) will deteriorate the azimuth imaging for MEOSAR and ionospheric effects become more and more serious with the increase of SAR altitude and the improvement of azimuth resolution designed.

Dynamics of interference interaction of counter-propagating electromagnetic pulses on a magneto-dielectric slab is studied in time domain. Energy redistribution in the counter-propagating pulses with arbitrary waveforms is considered. The maximal energy redistribution in the diffracted field takes place under certain conditions. The conditions are found and their physical explanation is supplied. The problem of transient electromagnetic wave diffraction on homogeneous magneto-dielectric slab is solved analytically by means of Laplace transform. The analytical solution is in agreement with numerical simulation based on finite difference time domain approach.

Sidelobes of strong targets substantially impact image quality of synthetic aperture radar (SAR) using linear frequency modulation (LFM) waveform, especially in urban areas. A novel space-borne azimuth multi-channel SAR scheme with ultra-low range sidelobe-ratio (RSLR) performance was proposed, employing complete complementary sequence (CC-S) coding waveform. The CC-S waveform was utilized to acquire ultra-low RSLR performance in range direction. Azimuth multi-channel scheme was introduced, to compensate reduction of effective PRF due to employing CC-S, and to mitigate azimuth resolution lost resulted from strong azimuth weighting, in order to implement low side-lobe performance in both range and azimuth direction. The method for pre-processing the CC-S based multi-channel SAR data was proposed, which would both compensate receiving time difference of sub-sequences and reconstruct azimuth spectrum of multi-channel SAR data. Furthermore, the corresponding image formation algorithm for accurately focusing raw data of the SAR system was also proposed. Computer simulation results were presented, which demonstrated the validity of the proposed SAR scheme and image formation algorithm.

This paper proposes a Synthetic Aperture Radar (SAR) vehicle target detection algorithm based on contextual knowledge. The proposed algorithm firstly obtains the general classification of SAR image with a Markov Random Field (MRF)-based segmentation algorithm; then modifies the prior target presence probability utilizing terrain types, distances to boundary and target aggregation degree; finally gains the detection results using improved Cell Averaging-Constant False Alarm Rate (CA-CFAR). Detections with real SAR image data show that this algorithm can effectively improve target detection rate and reduce false alarms compared with conventional CA-CFAR.

A 1.3 m piecewise reflectarray demonstrator has been designed, manufactured and tested, that radiates a contoured beam coverage over North America. A very good agreement is obtained between the theoretical and measured radiation patterns. Many innovative techniques and processes were developed in order to meet the challenging specifications of a space telecommunication antenna.

Software Defined Radar is the latest trend in radar development. To handle enhanced radar signal processing techniques, advanced radars need to be able of generating various types of waveforms, such as frequency modulated or phase coded, and to perform multiple functions. The adoption of a Software Defined Radio system makes easier all these abilities. In this work, the implementation of a Software Defined radar system for target tracking using the USRP platform is discussed. For the first time, an experimental characterization in terms of radar application is performed on the latest USRP NI2920, demonstrating a strongly improved target resolution with respect to the first generation platform.

High-performance dual-band Doherty power amplifier and non-uniform circularlypolarizedantenna array require impedance-transformingunequal dual-band 90° branch-line couplers forpower dividing and phase shiftingin the feed networks.In this paper, an analytical design methodology of generalized impedance-transforming dual-band branch-line couplers for arbitrary coupling levels is proposed. The coupler features wide range of realizable frequency ratio, multiple flexibleselections of open- or short-circuited and pi- or T-network topologies. For demonstration, four numerical examples with different parameters are presented.Furthermore, two microstrip couplers based on open-circuited pi- and T-network topologies were fabricated and measured.The measured results show good performance at dual 1.8/3.45 GHz bands.Thefractional bandwidthsdefined by the fluctuation of the coupling level and the phase difference less than ±0.5 dB and ±5°are up to 17% and 18%, 18% and 2% for open-circuited pi- and T-network topologies, respectively.

Failure mode characterization was applied to coplanar transmission lines by utilizing 0.5-10-GHz S-parameter measurements and post-calculated TDR (Time-Domain-Reflectometry) analysis. Coplanar waveguide transmission lines were inkjet-printed on 1.0-mm-thick flexible plastic RF substrates. Inductive, resistive, and capacitive types of failures-as the main failure modes caused by manufacturing, bending, or thermal cycling stresses-were investigated. The inkjet-printed CPW (Co-Planar Waveguide) lines were damaged by inductive shorts due to mechanical hits or resistive and capacitive failures due to bending of the substrate. By using the TDR method the type and physical location of the failure can be determined.