Two 60 GHz homodyne receivers dedicated for high-speed short-range communication systems are presented. The receivers are based on six-port and conventional (anti-parallel diodes) mixers, respectively. Comparative bit error rate results, function of local oscillator power, phase, and frequency shift over the operating bandwidth, are presented and discussed.
Application of artificial ground planes in design of compact cavity-resonance dual-band high-gain antennas is presented. The artificial ground plane consists of periodic strip grating on grounded dielectric slab. A code based on method of moment (MoM) is developed to analyze and design such artificial ground planes. The reflection parameters obtained using the MoM code are employed to characterize the surface impedance of the artificial ground plane for different incident angles and both TE and TM polarizations. Then, this impedance surface is used in transverse equivalent network (TEN) model of the cavity-resonance antenna with high-permittivity dielectric superstrate. Using TEN model radiation properties of such antennas are analyzed. Finally, the antenna with the compact size is designed to demonstrate the maximum directivity. An interesting characteristic of this antennas is that when the antenna ground plane acts as an artificial magnetic conductor the height of the antenna is almost reduced by a factor of two, while its directivity is increased by about 1 dB compared to the conventional antennas of this class having PEC ground plane.
A phenomenological theoretical model of grain dielectric properties is presented for radio and microwave frequencies. On the bases of this model, an inverse problem is solved to determine the dielectric permittivity of bound water inside kernels of winter wheat using results of complex permittivity measurements for bulk grain carried out by other authors. The character of the water complex permittivity dependence on frequency and kernel moisture content is studied. For this, the permittivity was considered as a sum of five different functions, depending on moisture content explicitly, and with coefficients being subject to determination. The frequency dependence of these coefficients was analyzed, and the regions typical for the ionic conductivity and for the dipole-orientational polarization mechanism were detected. For this polarization mechanism, the relaxation frequencies are differ from those of free water. It was concluded that water microparticles inside kernels are formed not by pure water, but by aqueous solution of four different substances coming from the kernel solid phase. It is shown that bound water, for the most part, is in a state that is intermediate between that of free water and that of molecules in the monomolecular water layer on the solid phase boundary.
Deterministic blind beamforming algorithms try to separate superpositions of source signals impinging on electromagnetic vector sensor array by using deterministic properties of the signals. This paper links electromagnetic-vector-sensor-array beamforming problem to the parallel factor (PARAFAC) model, which is an analysis tool rooted in psychometrics and chemometrics. Exploiting this link, it derives a deterministic blind beamforming algorithm. The blind beamforming algorithm doesn't require DOA (direction of arrival) information and polarization information. The simulation results reveal that the performance of the blind beamforming algorithm for electromagnetic vector sensor array is close to nonblind MMSE method, and this algorithm works well in array error condition.
In the present communication, we investigate theoretically and study a different type of photonic structure called metallic star waveguide (SWG) structure. The proposed structure, having single homogenous metallic material, is composed of a backbone (or substrate) waveguide along which finite side branches grafted periodically. In order to obtain the dispersion relation and hence the photonic band gaps (PBGs) of the SWG structure the Interface Response Theory (IRT) have been applied. Such types of structures show the band gaps without the contrast in the refractive index of the constituent materials. We also show that the range of forbidden bands can be tuned to different value by varying the number grafted branches of the SWG structures, without changing the other parameters. Moreover, the effects of variation of absorption of metals and plasma frequency on the band gaps of the proposed structures have been investigated.
This paper presents a circularly polarized (CP) GPS/DCS loop-like antenna with a microstrip feed. The proposed antenna comprised of a quasi-C antenna, an inverted-L sleeve strip connected with the ground plane and an L-shaped slit embedded in the ground plane. The C-like antenna generates a resonant mode with a poor impedance matching condition. The inverted-L grounded strip and the embedded L-slit are not only capable of modifying two orthogonal electric fields with equal amplitude and phase difference of 90 degree for radiating circular polarization at 1.575 GHz, but the impedance characteristics is also improved and the operating frequency is reduced. Both simulated and measured results are provided to validate the impedance and CP performance of the proposed antenna. For the optimized antenna case, the measured bandwidth with an axial ratio (AR) of less than 3 dB is larger than 19% and the measured impedance bandwidth of reflection coefficient S11 < −10 dB is about 30.1%.
In this paper, a new compact circular monopole ultrawideband antenna with multiple narrow bands notched is proposed, which is implemented by using the existing techniques, such as loading a L-type band-stop filter, inserting a split ring resonator (SRR), and the method we proposed that connecting L branches on the radiation disk. Four sharp notches at 2.4GHz, 3.5 GHz, 5.5 GHz, and 7.6 GHz are achieved separately. The measured VSWR shows a good agreement with the simulation results. The radiation patterns are obtained from Ansoft HFSS simulations and verified by CST Microwave Studio. The results prove that this kind of antenna can be applied in the UWB communication systems to avoid interference with other wireless systems, such as the 2.4GHz WLAN, 3.5 GHz WiMax, and 5.8 GHz WLAN etc. The parameters determining the antenna's band notched characteristic are discussed.
In this paper a novel ultra-thin radar absorbent material (RAM) using HIGP is presented and investigated. Owing to the high impedance property of the HIGP, the thickness of the RAM is about several tenths of the centre wavelengthof the absorption band, considerably thinner than conventional absorbers. The absorption band of the RAM is about several hundred megahertz. In the new RAM, lumped resistances are soldered between the patches of mushroom-like high-impedance surface (HIGP). And the metal ground plane of waveguide slot antenna is covered by this new type of RAM. As compared to the slot antenna with a metal ground plane, the measured results show that the radar cross section (RCS) of waveguide slot antenna reduces significantly. This proves that the new HIGP RAM has a good radar absorbing characteristics. The simulations and experiment results have shown that the RCS of antenna is reduced by 7.9 dB and gain is only reduced by 0.9 dB.
In the view of measuring directional fluctuations of a thin laser beam sent through a heated turbulent jet, an optical method using interference and diffraction with the out coming beam is proposed. The experimental set-up is described. A new technique for separating directional fluctuations of the laser beam is explained. From the measurement of the interference pattern perturbations, are deduced the Rms of the laser beam deflection angle, the spectrum of directional fluctuations of the laser beam, and the value of a scattering coefficient characterizing the heated turbulent jet. The measured spectrum reveals a -8/3 power law and the value obtained for that coefficient is nearly equal to that found in previous works. This agreement enables to conclude that the experimental technique used is efficient and satisfactory.
We experimentally studied the guidance properties of the S-shaped metamaterial slabs. A peek of transmitted power due to the bulk guidance modes is observed in the negative band of the metamaterial, which is larger than a conventional dielectric waveguide made of FR4. The peek transmission frequency is shown related with the change of the negative band of the S-shaped metamaterial slab. Our results show good agreement with the theoretical predictions.
Ametho d based on concurrent neuro-fuzzy system (CNFS) is presented to calculate simultaneously the resonant frequencies of the rectangular, circular, and triangular microstrip antennas (MSAs). The CNFS comprises an artificial neural network (ANN) and an adaptive-network-based fuzzy inference system (ANFIS). In a CNFS, neural network assists the fuzzy system continuously (or vice versa) to compute the resonant frequency. The resonant frequency results of CNFS for the rectangular, circular, and triangular MSAs are in very good agreement with the experimental results available in the literature.
A novel slot antenna that consists of an H-shaped slot encompassed by a rectangular metallic wall and a pair of C-shaped slots outside the wall is proposed. It features a unidirectional pattern, small electrical dimensions and medium gain. The H-shaped slot radiates as an inductively loaded magnetic dipole while the induced electric currents on the vertical wall radiates as electric dipoles. The front-to-back ratio (FBR) of the antenna can be controlled by proper constructive and destructive interferences of radiating fields of the magnetic and electric dipoles. The size of the ground plane can be reduced by the use of the C-shaped slots that confine the currents to the proximity of the metallic wall. Two prototype antennas operating at 2.4 GHz were designed. By adjusting the structure parameters, the front-to-back ratio of the antenna can be conveniently altered. The first prototype has an impedance bandwidth (BW) of 3.8% for SWR ≤ 2, a 4.6 dBi gain, a 10-dB FBR and a ground size of 0.84λ0 × 0.64λ0 where λ0 is the free-space wavelength at the center frequency. The corresponding figures of the second prototype are 1.83%, 4.1 dBi, over 20 dB and 0.64λ0 × 0.64λ0. Both antennas have a height of 0.128λ0.
This study investigated the relationship between temperature elevation and spatial-average SAR (specific absorption rate) in a head model of a Japanese male due to a dipole antenna. The frequencies considered are in the range between 800MHz and 3 GHz, which are used in wireless communications. Our attention focuses on the average mass of SAR which maximizes the correlation with local temperature elevation. Computational results suggested that an appropriate averaging mass of SAR did not exist over wide frequencies, which was attributed to the frequency-dependent penetration depth of electromagnetic waves. For most cases considered in this study the SAR averaging over 10 g was better than that for 1-g from the standpoint of correlating the temperature elevation. The dominant factor influencing this averaging mass is the thermal diffusion length which largely depends on the blood perfusion rate. Additionally, the heat evolved in the pinna played an important role in the correlation between spatialaverage SAR and temperature elevation.
In this paper, the Parallel Finite-Difference Time-Domain (FDTD) method based on MPI (Message Passing Interface) is applied to analyze the EMC problems of the electrically large platforms accurately and quickly, which is a full-wave numerical method. The MPI library and domain decomposition method are applied to implement the Parallel FDTD method, so that the computation resource is expanded. The method can analyze the EMC problems by modeling the electrically large platforms accurately. Then the network theory is introduced to compute the isolation between antennas combined with the Parallel FDTD method firstly, which avoids the complexity of sweeping frequency and reduce the computing time greatly. Numerical results show that the method is correct and efficient. Finally, the EMC problems of antennas mounted on electrically large platforms are analyzed and some useful conclusions are obtained.
Exploitation of the backscattered field polarization over the wide electromagnetic spectrum, from visible to microwave frequencies, provides an approach to advanced target recognition in remote sensing applications. The framework for full coherent characterization of the scattered field that is established here, maximizes the extracted target information. It is also shown that such a methodology, which is theoretically similar to the concept of "partial or compact polarimetry", yields comparable results to full or quadrature-polarized systems by incorporating judicious assumptions and assuming/implementing optimal transmitted or illumination field polarizations. On this basis, common characteristic features, interworking and fusion of different polarimetric sensor products in different regions of spectrum, e.g., radar/SAR and Electro-Optical, are investigated and formulated within a robust framework based on full coherent treatment of the scattered field.
This paper deals with the design of beam-forming networks (BFN) for scannable multibeam antenna arrays using Coherently Radiating Periodic Structures (CORPS). This design of CORPS-BFN considers the optimization of the complex inputs of the feeding network by using the Differential Evolution (DE) algorithm. Simulation results for different configurations of CORPS-BFN for a scannable multibeam linear array are presented. The results shown in this paper present certain interesting characteristics in the array factor response for the scannable multibeam linear array and the feeding network implification for the design of BFN based on CORPS.
To investigate the effect of forest spatial structure on SAR interferometry (InSAR) data requires an electromagnetic scattering model capable of expressing radar observation in terms of parameters describing forest spatial structure. In this paper, we propose an electromagnetic scattering model for mixed-species forest which includes the coherent effect of forest structure and preserves phase information of radar backscattering signal. Interferometric SAR images of three-dimensional (3-D) scenes are simulated based on this model and the heights of scattering phase centers are estimated from the simulated InSAR data. The results show that the model is suitable for simulating interferometric SAR response to forest canopies and for investigating the forest spatial structure. We also compare the backscattering coefficients predicted by the proposed electromagnetic scattering model with the JERS-1 L-band SAR and ENVISAT ASAR C-band data acquired at forest stands of Changqing test site in Daxinganling, Northern China. Good agreements are obtained between the model results and measurement data.
In this paper, a folded substrate integrated waveguide (FSIW) cavity is analyzed theoretically. Formulae for the determination of the dimensions of the FSIW cavity have been deduced. To verify the proposed formulae, simulated results are compared with the results of the formulae and good agreement has been observed between them. An example filter working at 8 GHz is designed and fabricated. Good agreement between the simulated and the measured results has been obtained. Result shows the advantage of wide out-of-band rejection and compact size.
The full MIMO radar and the partial MIMO one are introduced. The performance analysis of beamforming for MIMO (Multiple-input Multiple-output) radar and comparisons with the phased-array radar are given. The expressions of beamwidth, gain loss and detection range for MIMO radar are derived. Theoretical analysis and simulations show that the beam of the full MIMO utilizing all virtual array elements is identical to the two-way beam of the phasedarray radar, and that the beam of the partial MIMO selecting elements with different phase centers (phase shifts) is narrower, but has a gain loss. Additionally, the partial MIMO can avoid aliasing in space when the transmitting antennas are spaced at greater than half-wavelength spacing. As scanning radar, the partial MIMO radar has smaller detection range than the phased-array radar, and the full MIMO radar has the same range as the phased-array radar.
The measurement of inhomogeneity and irregularity of dielectric plate requires metering equipments with high spatial resolution power and contactless method. As we know, a measurement system with thin beam has high spatial resolution power. In this paper, a beam compressed system (BCS) is proposed to improve the spatial resolution power for measuring inhomogeneity and irregularity of dielectric plate at millimeter wave band. The beam shape of the BCS has to be carefully designed to achieve a very thin shape which has to be constant over a long range. The BCS can be applied to detect inhomogeneity and irregularity of a dielectric plate from cell to cell with its thin beam. Simulations with FDTD and FEM and experiments are carried out to confirm the performance of the designed BCS, both simulation and experimental results have good agreement. And the images of the permittivity or thickness variance of dielectric plate are given to demonstrate the advantages of the BCS over traditional Gaussian beam measuring method.
The sensitivity of cylindrical and spherical transformation cloak to several factors has been carefully studied in this paper. We find that the performance of the transformation cloak is quite sensitive to the crevice in the shell. When an obstacle is not completely wrapped inside the cloaking shell,noticeable scattering will be induced outside. It is also shown that if the shape of the cloak is changed in certain ways while the material parameters remain the same,the backward scattering is still zero. In addition,the combination of parts of cylindrical cloak can only achieve perfect invisibility in one direction,while combining the cylindrical cloak with two halves of spherical cloak can still make a perfect 3-dimensional (3D) invisible cloak. The findings are verified with finite element based simulations as well as theoretical calculations. Our discussion results are valuable to the implementation of cloak in engineering.
The modifiedWatson transform is applied to the Mie series expression of the electromagnetic field scattered by a high frequency plane wave incident on an infinitely long double negative cylinder. The Debye expansion is applied to the Mie series coefficients to obtain a physical insight into the scattering mechanisms and achieve an efficient approach for the computation of the scattered field. The first two terms of the Debye series are computed using the residue series in the geometrical shadow regions and using the steepest descent method in the geometrically lit regions. It is observed that the results obtained from the series and from the modified Watson transform are in good agreement. The angular boundaries for the geometrically lit and the geometrical shadow regions of the double negative cylinder corresponding to the first two terms of the Debye series are determined. These are compared with the corresponding angular boundaries for a double positive cylinder. It is observed that the spatial extent of the geometrical shadow of the double negative cylinder corresponding to the second term of the Debye series is very small compared to that of the double positive cylinder due to the negative refraction in the double negative cylinder when the magnitude of the refractive index n is greater than √2.
This paper talks about the adiabatic parameter dynamics of Gaussian and super-Gaussian optical solitons that propagate through dispersion-managed optical fibers. These parameter dynamics are useful in further study of various aspects of optical solitons, including the quasi-particle theory of optical solitons, collision induced timing jitter, the four-wave mixing and various other features. These perturbation terms and its corresponding adiabatic dynamics also can be used to study the aspects of ghost pulses and the effects of randomness in dispersion-managed optical fibers.
The imaging method when a lossy layer (e.g., a defected metallic slab or a plasma layer) is present between the target and the sensor is demonstrated using the concept of active left-handed material (LHM). The effect of the lossy layer to the reflection coefficients measured by the receiver can be cancelled by imaginatively adding an active LHM layer, which has a same thickness as the lossy layer but an opposite sign of the constitutive parameters. Therefore, the updated reflection coefficients obtained after this data process look like the lossy layer has been removed, which leads to a significant improvement of the target imaging. When the lossy layer is inhomogeneous due to the existence of small defects, we use a homogenization procedure based on the Drude model to characterize its effective constitutive parameters. Our simulation examples shows the effectiveness of the proposed method.
When airborne forward looking planar antenna is used to detect ground moving target, targets may be masked by strong clutter due to high sidelobes of the antenna pattern. In this paper, transmitting pattern is synthesized via convex optimization in order to suppress clutter from ground. Transmitting pattern has a low sidelobe illuminating short ranges and a high sidelobe focused into sky and remote ranges, which results in a relative small beamwidth in the elevation plane. In the azimuthal plane, transmitting pattern can form some notches in some fixed directions where strong clutter and interference exist. With insufficient training data due to a dispersion of clutter spectrum along range, adaptive receiving pattern with low sidelobes can be obtained by convex optimization when detecting remote targets. Simulation results show that transmitting and receiving patterns can effectively be designed via convex optimization for airborne forward looking radar.