A self calibration algorithm for direction finding in the presence of arbitrary shape 3D scatterers of resonating size is presented. This algorithm removes the effects of mutual coupling and 3D scatterers on direction of arrival estimation. The scatterers and wire type antenna array are excited by incident plane waves of arbitrary direction. The 3D scatterers shape is approximated as a sphere, thus spherical harmonics are assumed to be originated in response to the plane wave excitation. The algorithm requires the location of the scatterers with reference to antenna elements. However, knowledge of exact shape of scatterers is not required. Moreover, scatterers may be located in near or far fields. The work is supported by numerical examples for different scenarios of multiple incident waves and scatterers.

The aim of this work is to implement a hybrid approach able to provide an efficient solution of the electromagnetic coupling between an antenna and an obstacle distant few meters away. The idea is to divide the problem into a small number of less complex sub-problems exploiting the advantage of generating the admittance matrix that describes the scattering problem by a numerical code. To this end, the electromagnetic field impinging on the object has been characterized by means of a proper number of very narrow beams; for each beam the scattering problem has been solved by a commercial code; finally, the total admittance matrix has been obtained as composition of all the scattering contributions. The resulting echoof a moving obstacle has been compared with that measured by experimental investigations, both for metallic and dielectric bodies.

A compact chiral metamaterial is proposed and comprehensively investigated that can achieve circularly polarized wave emission from linearly polarized incident wave (giant circular dichroism) over dual bands and near Diodelike asymmetric transmission of linearly polarized waves. The chiral metamaterial also features exceptionally strong optical activity. For verification, two proof-of-concept slab samples are designed, fabricated and measured at microwave frequencies. Numerical and experimental results agree well, indicating that the former dual-band circular polarizer features high conversion efficiency around 8.1 and 9.9 GHz in addition to large polarization extinction ratio of more than 16 dB, while the latter chiral sample enables the near 90% cross-polarization transmission in one direction and almost 10% transmission in the opposite direction. The block "meta-atom" that utilized to build the ultrathin CMM slab is less than λ0/6.73 evaluated at operating frequency. Good performances of the two chiral slabs with simple and compact package suggest promising applications in the circular polarizers (circulators) and transparent linear polarization transformers or spectrum filters (isolators) that need to be interpreted with other compact devices.

In this paper, we describe two parallel MRTD algorithms. Both algorithms are proved to be feasible by comparing the result of the serial MRTD method, the efficiency of them are also compared in order to evaluate a better strategy. Moreover, a novel implementation of "complex frequency-shifted" perfect matched layer (CFS-PML) with auxiliary differential equation (ADE) is presented for the MRTD method. The implementation is easier to obtain and more memory saving when treating more generalized media, and numerical results demonstrate that the CFS-PML with ADE is more absorptive than the popularly used APML. Furthermore, using one of the parallel algorithms and the CFS-PML, the characteristic of the field cross-section distribution of the electromagnetic pulse (EMP) propagation in vaulted tunnel is studied.

In this paper, the design of a single-feed triple-band circularly polarized Spidron fractal slot antenna is presented. The proposed antenna is composed of a Spidron fractal slot, a Z-shaped slit, and two L-shaped slits to realize triple-band circular polarization operation. A simple 50 Ω microstrip line is utilized to feed the proposed antenna. A conducting reflector is also used to reduce back radiation, thereby enhancing the forward antenna gain. The proposed antenna has total dimensions of 40.7 mm × 40.7 mm × 18.52 mm (0.42λ × 0.42λ × 0.19λ) and was fabricated and tested. The experimental results show that the proposed antenna has -10 dB reflection coefficient bandwidths from 2.76 GHz to 3.13 GHz and from 3.56 GHz to 6.22 GHz. The measured 3 dB axial ratio bandwidths are 2.28% (3.04-3.11 GHz) for the lower band, 7.15% (4.18-4.49 GHz) for the middle band, and 2.6% (4.93-5.06 GHz) for the upper band. The peak gains within the -10 dB reflection coefficient bandwidths are 3.41 dBic and 6.29 dBic, respectively.

UWB antenna is a crucial part of any UWB system required for indoor application. In this paper a novel design is presented, which relies on self-complementary structure. The structure is fed by a microstrip line, where a triangular notch is embedded in the ground plane. The design in this paper yields a UWB bandwidth that extends from 2.86.0-40.0 GHz. To ensure coexistence of UWB with WLAN applications (5.15-5.825 GHz) with minimal interference, a frequency notch is introduced using two parasitic U-shaped elements embracing the microstrip feeding line that resonates in the vicinity of the band notch frequency band. The proposed design was subject to parametric study to reach optimum parameters. The final design was fabricated using photolithographic technique and the measured results showed very good agreement with simulated ones.

The objective of the work is to design a dual frequency microstrip antenna for small frequency ratio applications. The proposed geometry comprised of suspended truncated circular microstrip antenna, with double U slot etched on the radiating element. The design parameters are radius of circular patch, width and length of slot, height of air gap. The proposed design of the antenna has enough freedom to control the dual design frequencies/frequency ratio by varying the above design parameters. FR4 substrate with dielectric constant 4.4 is chosen for design and fabrication. The dual design frequencies are 1.93 GHz and 2.17 GHz, covering the applications such as WCDMA, 3G mobile data terminals, and 4G LTE applications. The antenna is fed by a 50 Ω coaxial probe. The simulation of the antenna is performed using ANSOFT HFSS and analyzed for return loss, VSWR and radiation pattern. The antenna is fabricated and tested for impedance matching and radiation characteristics. The simulation and experimental results show that the antenna worked well at desired dual frequencies. The impedance matching is well at both frequencies (VSWR <2). Though, the measured radiation pattern is unidirectional in co-polarisation, nearly omnidirectional (butterfly) pattern is obtained in cross-polarisation and gain is about 5.54 dB at 1.93 GHz and 8.23 dB at 2.17 GHz. Also, the design is well suited for small frequency ratio dual frequency applications.

In this paper, a three-pole bandpass filter (BPF) using a new defected ground structure (DGS) is discussed. The proposed DGS is incorporated in the ground plane under the feed lines and the coupled lines of a bandpass filter to improve the performance of the filter in both passband and stopband. The banpass filter is designed with a center frequency of 1.8 GHz and a bandwidth of 270 MHz. The suppression of better than 20 dB was achieved for frequencies between 2.2 and 5 GHz. A prototype of BPF was fabricated and tested. Prototype measured data was in good agreement with simulation results.

The development of anatomically and dielectrically representative tissue models is key to the design and refinement of electromagnetic based diagnostic and therapeutic technologies. An important component of any such model are accurate and efficient Debye models which allow for the incorporation of the frequency dependent properties of biological tissues. The establishment of multi-pole Debye models is often a compromise between accuracy and computational cost. Furthermore, some finite difference time domain schemes impose constraints on the minimum Debye pole time-constant. In this study, the authors have developed an optimised genetic algorithm to establish Debye coefficients with minimal yet sufficient Debye poles for several different biological tissues. These Debye coefficients are fitted to existing Cole-Cole models and their accuracy is compared to previously fitted Debye models.

In most practical applications of the phased array antennas, the generated nulls toward the interfering signals should have enough depth and width to accommodate fluctuations in frequency and direction of the interferer. Due to these fluctuations, the nulls can be easily deviated from its desired angular locations in the traditional adaptive nulling arrays since the nulls are very sharp and sensitive. An innovative technique for wide nulling arrays has been recently presented. The wide nulls can be introduced by setting properly the excitation coefficients of the two edge elements of the antenna array. In this paper, the effect of frequency fluctuation on the nulling performance is investigated. By generating wide and deep nulls toward and around the interference directions, the proposed method provides robustness against frequency fluctuation. Simulation results in realistic situations with frequency fluctuation are presented to illustrate the performance of the proposed technique. Comparisons with the standard fully adaptive nulling array are shown.

High reflective materials in the microwave region play a very important role in the realization of antenna reflectors for a broad range of applications, including radiometry. These reflectors have a characteristic emissivity which needs to be characterized accurately in order to perform a correct radiometric calibration of the instrument. Such a characterization can be performed by using open resonators, waveguide cavities or by radiometric measurements. The latter consists of comparative radiometric observations of absorbers, reference mirrors and the sample under test, or using the cold sky radiation as a direct reference source. While the first two mentioned techniques are suitable for the characterization of metal plates and mirrors, the latter has the advantages to be also applicable to soft materials. This paper describes how, through this radiometric techniques, it is possible to characterize the emissivity of the sample relative to a reference mirror and how to characterize the absolute emissivity of the latter by performing measurements at different incident angles. The results presented in this paper are based on our investigations on emissivity of a multilayer insulation material (MLI) for space mission, at the frequencies of 22 and 90 GHz.

Two dimensional (2D) radar coincidence imaging is an instantaneous imaging technique which can obtain 2D focused high-resolution images using a single pulse without the limitation to the target relative motions. This paper extends the imaging method to three dimensions. Such a three-dimensional (3D) radar imaging technique does not rely on Doppler frequency for resolution and has an extremely short imaging time (shorter than a pulse width), resulting in two remarkable properties: 1) it does not require the relative rotation between targets and radar; 2) it can considerably avoid the image blurring in processing noncooperative targets without motion compensation. 3D radar coincidence imaging consequently can derive high-quality images for either the targets that are stationary with respect to radars or the ones in maneuvering 3D rotations. The validity of the proposed imaging technique is confirmed by numerical simulations.

The difficulty of focusing high-resolution highly squinted SAR data comes from the serious azimuth-range coupling, which needs to be compensated in the procedure of imaging. Generally, the linear range walk correction (LRWC) can reduce the coupling effectively, however, it also induces the problem of azimuth-dependence of residual range cell migration (RCM) and quadratic phase. A novel algorithm is proposed to solve this problem in this paper. In this algorithm, the azimuth nonlinear chirp scaling (ANCS) operation is used, which can not only eliminate the azimuth space variation of residual RCM and frequency modulation (FM) rate but also remove the azimuth misregistration. In addition, the range chirp scaling operation is applied to correct the range-dependent RCM. After implementing the unified RCM correction, range compression and azimuth compression sequentially, the focused SAR image is acquired finally. The experimental results with simulated data demonstrate that the proposed algorithm outperforms the existing algorithms.

The propagation properties of a Lorentz-Gauss vortex beam in a turbulent atmosphere are investigated. Based on the extended Huygens-Fresnel integral, the Hermite-Gaussian expansion of a Lorentz function, etc., analytical expressions of the average intensity, effective beam size, and kurtosis parameter of a Lorentz-Gauss vortex beam are derived in the turbulent atmosphere. The spreading properties of a Lorentz-Gauss vortex beam in the turbulent atmosphere are numerically calculated and analyzed. The influences of the beam parameters on the propagation of a Lorentz-Gauss vortex beam in the turbulent atmosphere are examined in details. Upon propagation in the turbulent atmosphere, the vale in the normalized intensity distribution of a Lorentz-Gauss vortex beam gradually rises. The rising speed of the vale is opposite to the spreading of the beam spot. When the propagation distance reaches to a certain value, the Lorentz-Gauss vortex beam in the turbulent atmosphere becomes a flattened beam spot. When the propagation distance is large enough, the beam spot of the Lorentz-Gauss vortex beam tends to be a Gaussian-like distribution. This research is beneficial to optical communications and remote sensing that are involved in the single mode diode laser devices.

Most three-dimensional omnidirectional cloaks proposed to date (using optics, electromagnetics, and acoustics) are not easily realized, as they possess inhomogeneous and singular parameters imposed by the transformation-optic method. In this study, we theoretically demonstrate that a thermodynamic spherical cloak with homogeneous and finite conductivity and employing only naturally available conductive materials may be achieved. More interestingly, the thermal localization inside the coating layer can be tuned by anisotropy, which may lead to nearly perfect functionality in an incomplete cloak. The practical realization of such a homogeneous thermal cloak by using two naturally occurring materials has been suggested, which provides an unprecedentedly plausible way to flexibly achieve a thermal cloak and manipulate heat flow. Numerical experiments validate the excellent performance of the proposed homogeneous cloak functions.

A polarization reconfigurable spiral slot antenna with polarization states switched among left-hand circular polarization (LHCP), right-hand circular polarization (RHCP) and linear polarization (LP) is proposed in this paper. The antenna consists of a coplanar waveguide (CPW) input, a pair of reconfigurable CPW-to-slotline transitions, two separated same size single-arm spiral slot radiators, and four PIN diodes for reconfigurability. A good impedance match (VSWR≤2) for both linear and circular polarization is achieved from 2.1 to 2.9 GHz. The bandwidth for axial ratio AR≤3 dB for both RHCP and LHCP states ranges from 2.27 to 2.66 GHz (15%). The simulation and measurement results agree well and hence sustain the reconfigurability of the proposed design.

A design procedure for microstrip antenna topologies operating within the full UWB band is described. The presence of the full ground plane successfully results in a unidirectional antenna, which is important in applications related to Wireless Body Area Networks (WBAN). The existing broadbanding concepts have been creatively combined throughout the design to enable the UWB behavior, while simultaneously keeping the full ground plane intact. The procedure is validated with a concrete design of a microstrip type UWB antenna operating from 3.6 GHz to 10.3 GHz.

To cope with the energy shortage and the rising cost of the fossil fuel, many wind farms are being constructed under the supervision of Korean government along the coasts of Korean peninsula to generate clean and renewable energy. However, construction of these wind farms may cause negative effect on various L-band radars in operation. This paper presents the result of the micro-Doppler (MD) analysis of the influence of the wind turbine on the L-band radar using the point scatterer model and the radar cross section of the real turbine predicted by the method of physical optics. The simulation results obtained at three observation angles show that the range of MD occupies a considerable portion of the helicopter MD range, and thus, the operations using helicopters need to be avoided in the wind farm region, and additional radars are required for the recognition of helicopter-like objects.

A novel Frequency Selective Surface (FSS) configuration is proposed for the design of polarization-insensitive metamaterial absorbers operating below 1 GHz, where the first resonances of small commercial enclosures appear. The novel FSS shows a strong subwavelength response, enhanced by the dielectric substrate, which allows the design of compact planar absorbers with excellent angular and polarization stability.

This paper proposes an investigation in the terahertz (THz) frequency range of the dispersion and an individual quantitative treatment of the losses of the most classical microwave waveguides (coplanar, slotline, microstrip and stripline) numerically led in three dimensions (3D). An original strategy has been used to quantify radiation losses associated with leaky modes. A very low THz permittivity polymer (benzocyclobutene (BCB)) was used as a very convenient substrate to be easily grafted as a THz environment of integrated passive or/and active devices. Direct comparisons of the losses and the dispersion have been performed following two criteria: a constant characteristic impedance Z_c fixed at 100 Ω and a constant effective width Weff fixed at 30 μm. The best waveguides are microstrip (α_T= 2.52 dB/mm for Z_c= 100 Ω and for W/H=35/50 μm (with W the strip width and H the substrate height) and α_T =2.29 dB/mm for W_eff = 30 μm at 1 THz with H = 30 μm) and stripline (with quasi-null radiation losses and the best quality factor Q_T= 63 for Z_c = 100 Ω). The large dispersion and radiation losses of the slotline (SL) can be reduced with a thick BCB encapsulation to enhance the THz signal. The coplanar waveguide (CPW) remains in a medium position. Besides the parasitic mode (SL) and low Q_T problems due to mainly ohmic losses, its major advantage is its planar geometry allowing to an easy circuit integration with THz sources, amplifiers and detectors based on semiconductor. Consequently, these THz studies on BCB microwave standard waveguides open to various perspectives to carry out a broad panel of integrated THz circuits.