In this contribution, a design approach for the realization of broadband Doherty Power Amplifiers (DPAs) is proposed and demonstrated. The methodology is based on the exploitation of the wideband response of 2-sections branch-line couplers both as input splitter and output combiner of the DPA. These couplers are designed through a CAD optimization process which is specificaly oriented to the developement of DPAs. The method is also applied to realize a GaN based hybrid prototype that shows more than 36% of fractional bandwidth around 2 GHz frequency range, validated through single carriers and modulated signals (3gpp and WiMax). In single carrier mode an efficiency higher than 41% (>50% in saturation, with a peak of 72%) is obtained in 6 dB of output power dynamic range in the entire operating band. Experimental sesults with 5 MHz 3 gpp and WiMax signals shown an average efficiency of 50% and 45% when 37 dBm and 34 dBm of average output power are reached, respectively.
A novel prism phase modulator (PPM) for phase difference modulation between pand s-polarization lights in a surface plasmon resonance phase-sensitive imaging sensor is proposed in this paper. The PPM consists of a rhombic prism (to obtain a curve of phase difference between the two polarizations), a rotation stage and a mirror. The PPM shows great modulation stability and helps to achieve a high detection resolution. Surface plasmon resonance phase imaging is realized with a microfluidic device and a CCD camera. Experimental result shows that the detection resolution of our SPR-PI sensor based on phase-interrogation method is 7.61×10-7 RIU with hydrous samples, which is 16 times improved compared with that based on intensity-interrogation. Real-time monitoring of the interaction between Angiogenin and anti-Angiogenin is also illustrated.
Effects on the communication signals caused by the time-varying plasma sheath surrounding hypersonic vehicles are investigated. Using computational fluid dynamics (CFD) technique, Demetriades's plasma turbulence model and finite-difference time-domain (FDTD) algorithm, amplitude variation and phase fluctuation induced by plasma electron density turbulence are obtained, and their statistical properties are analyzed and characterized. Furthermore, a finite-state Markov channel (FSMC) model is proposed, to represent the dynamical effects on electromagnetic wave propagation through plasma sheath. With high accuracy and greatly reduced complexity, the FMSC model could be very useful to develop novel communication techniques for alleviating the radio blackout problem.
While Archimedean spiral antennas were invented a half-century ago, only self-complementary impedance can be evaluated directly from the Babinet's principle. This paper examines the effects of metal width and arm spacing on printed spiral's input impedance. A model is proposed based on examination by decomposition of planar spiral. A closed-form expression for the input impedance of Archimedean spiral antenna is obtained by evaluating the proposed model with conformal mapping techniques. Full-wave numerical simulations, Babinet's principle, and a fabricated antenna demonstrate the accuracy of the proposed model. The expression in this work can be used to find the impedance of a variety of spiral complementary structures analytically. The examination and discussion on the effects of other parameters and features in addition to the spiral itself are also provided through numerical simulation.
An improved method of quality guided phase unwrapping (QGPU) is proposed in this work. It extracts the quality map via a median filtered phase derivative variance (MFPDV) that applies a twodimensional median filter on the phase derivative variance (PDV) map, in order to reduce the effect of noise in the background area. In addition, we employed the Indexed Interwoven Linked List (I2L2) structure to store the orderly adjoin list more efficiently and the Two Section Guided Strategy (TSGS) to reduce comparison frequency. The experiments demonstrate that the normalized L1 norm of MFPDV of a brain MR image is only 0.0827, less than that of PDV method at 0.0923. Besides, the computation time of QGPU with I2L2 technique is only 30% of that with sequence structure, and the computation time of QGPU with TSGS is only 65% of that without TSGS. In total, the proposed MFPDV upwrap phase images better than conventional PDV map, and I2L2 and TSGS are efficient strategies to reduce computation time.
In this paper, a bi-layer twisted split-ring structure asymmetric chiral metamaterial was proposed, which could achieve circularly polarized (giant circular dichroism effect) wave with dual bands and linear polarization transformation (giant optical activity)with asymmetric transmission wave emissions simultaneously from linearly polarized incident wave at microwave frequencies. Experiment and simulation calculations are in good agreement, indicating that the dual-band circular polarizer features high conversion efficiency around 5.32 GHz and 6.6 GHz in addition to large polarization extinction ratio of more than 16 dB, while cross linear polarization transformation with asymmetric transmission is observed around 10.52GHz. The transformation behavior for both circular and linear polarizations could be further illustrated by simulated surface current and electric field distributions. The proposed asymmetric chiral metamaterial structure could be useful in designing novel EM or optical devices, as well as polarization control devices.
The microwave polarimetric scattering from two-dimensional (2-D) wind fetch- and water depth-limited nearshore sea surface is investigated by using the second-order small-slope approximation (SSA-II). The sea waves are simulated by taking into account the influences of fetch and depth. Based on this, the joint influence of fetch and depth on the normalized radar cross section (NRCS) of sea surfaces for both co-polarizations and cross-polarization in different wind directions is mainly studied. Monostatic and bistatic numerical results both indicate that in the marine environment of small depth and large fetch, the nonlinear interactions among waves become more intense, which has a greater impact on NRCSs for co-polarizations than their cross-polarized counterparts. Comparison of the results for different wind directions also reflects that the backscattered echoes along wind direction have much greater strength, regardless of the magnitude of wind fetch and water depth.
To reduce the complexity of classifier design in radar automatic target recognition (RATR), a novel RATR method for high range resolution profile(HRRP) is proposed. Linearly separable features are extracted with sequential vanishing component analysis (SVCA) which is implemented by finding the generators of each approximately vanishing polynomial set, and target classification is implemented with linear classifiers. Experiments are carried out on simulated vehicle target data and MSTAR database, and the results demonstrate the efficiency of the proposed method.
In this paper, a delivery system allowing simultaneous microwave heating and real-time spectrofluorometric measurements in biological systems is proposed and characterized. This system is used to investigate the phase behavior of lipid bilayers from about 15°C to 45°C. The delivery system is based on an open transverse electromagnetic (TEM) cell combined with a spectrofluorometer via an optical cable system. A numerical and experimental dosimetry of the delivery system is conducted. The Specific Absorption Rate (SAR) efficiency of the system is 26.1±2.1 W/kg/W. Spectrofluorometric measurements on Laurdan labeled small unilamellar vesicles (SUVs) are carried out. Generalized polarization (GP) of the SUV' membrane is obtained from the fluorescence intensities measured at two emission wavelengths.
This paper deals with the modeling of the brushed DC motor used as a reinforced starter for a micro-hybrid automotive application. The aim of such a system, also called ``stop-start'', is to stop a combustion engine when the vehicle pulls to a stop, and to restart it when the driver accelerates. A reinforced starter is able to ensure this new function in addition to the classical cold start. Then, its life time has to be widely increased in comparison with a classical starter. They have to be optimized, and more especially their process of commutation in order to minimize commutator and brush wears, and thereby increase the lifetime of the device up to the whole life of the vehicle. The main contribution of the paper is the development of a coupled FE-circuit model taking into account local saturation and arc phenomena. Brush-segment contact resistance introduced in the circuit model has been computed efficiently and compared to measures. The whole model has been validated by experimental measurements which are carried out with specific experimental test benches.
We propose a general method to design an arbitrarily shaped radome which can extend the scanning angle of a phased array antenna through finite embedded transformation (FET). The main advantage of our method is that the relationship between the incident angle and steered output angle of the radome can be designed in advance (e.g., a linear relation can be achieved). Unlike a traditional FET, which is often applied onto a slab region, we first apply FET onto an arbitrarily shaped region to bestow the desired radome with an arbitrary shape. Two specific examples have been given to demonstrate our method. Numerical simulations show good performance of our radome.
Implanted antennas are widely used in hyperthermia and biomedical applications. The antenna needs to be extremely small while maintaining a permissible Specific Absorption Rate (SAR) and being able to cope with the detuning effects due to the dielectric properties of human body tissues. Most of the proposed antennas for implanted applications are electric field antennas such as Planner Inverted-F Antennas (PIFA) and micro-strip patch antennas. By minimizing the size of an electric field antenna, the near zone electric field will increase, resulting in higher SAR. This work is devoted to design a miniaturized magnetic field antenna to overcome the above limitations. The proposed electrically coupled loop antenna (ECLA) has high magnetic field and low electric field in the near zone and therefore, has a small SAR and is less sensitive to detuning effects. ECLA is designed at the Medical Implanted Communication Service (MICS) band with dimensions of (5×5×3 mm3). ECLA has been simulated inside one-layer human body model, three-layer spherical human head model, human head and human body. From the simulation results, ECLA inside the human body has a 5 MHz -3 dB bandwidth, -14 dB gain, and radiation efficiency of 0.525%. The 1 g average SAR inside the human body for 10 mW input power is about 1 W/kg which is 7 times lower than the SAR for a patch antenna of the same size with the same accepted power.
The paper presents a methodology to achieve efficient low-profile electromagnetic bandgap (EBG) antennas based on thick EBG unit cells. The EBG cells are composed of thick metal patches separated by narrow high aspect ratio (HAR) gaps, and positioned on a PEC-backed substrate. This approach yields new miniaturized EBG cells with considerably reduced electrical size. The miniaturized cells are employed to demonstrate new compact self-excited EBG resonator antennas with considerably reduced operating frequencies. Full-wave simulations and experimental results demonstrate the design approach.
An ultra-thin triple-band metamaterial absorber (MA) is proposed in the microwave region, which is composed of a periodic array of three rotated square rings (RSRs) and a continuous metal film separated by only 1 mm dielectric substrate. The fabricated MA exhibits three experimental absorption peaks at 4.88 GHz, 7.88 GHz, and 11.32 GHz with the corresponding absorption rates of 98.8%, 96.5%, and 95.9%, which shows an excellent agreement with the simulated results. The triple-band MA is polarization-insensitive at the normal incidence. Finally, the multi-reflection interference theory is introduced to interpretate the absorption mechanism. The calculated absorption rates of the improved unit cell for the strongly coupled MA coincide well with the simulated results at wide angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves.
A new design for a compact and wideband circularly-polarized rectenna with high efficiency operating at X-band is proposed. A dual-slot coupled antenna excited by an H-shaped slot fed by a T-shaped microstrip is designed to yield wideband performance as a receiving array antenna. Rectifying circuit models for harmonic suppression circuit, impedance matching, DC-pass circuit, and DC return circuit at the input and output of the diode are built up and optimized to transfer the maximum power from the antenna to the load using an ADS circuit simulator. An RF-DC conversion efficiency of 71.9% is measured on the conditions of 300 load, and 50.1 mW RF input power at 9.5 GHz operating frequency. For the proposed wideband rectenna, the efficiency of more than 50% is measured over a 1 GHz frequency bandwidth. The measured gain, axial ratio, and return loss of the circularly polarized antenna with a 4-element array are 11.2 dBi, 1.1 dB, and -16.4 dB, respectively. The reflection coefficient of the array antenna is measured at less than -10 dB over a wide frequency range of about 2 GHz. Using this antenna as transmitting (TX) and receiving (RX) radiators, the free-space power transfer capability of the rectenna is tested in free space to turn on an LED at 25 cm distance.
For microwave tomography applications, we show that the utilized incident field distribution can affect the achievable image quantitative accuracy and resolution. In particular, for the synthetic cases considered here, it is shown that the use of a focused incident field distribution within the imaging domain often results in either enhanced or equivalent image reconstruction as compared to the use of an omnidirectional incident field distribution.
The traditional pattern synthesis method of space-borne array is to achieve a ``iso-flux'' beam coverage via approximating a desired pattern; however, the synthesized pattern may not optimize the whole satellite communication (SatCom) system performance. This paper analyzes the interference in multibeam SatCom system using CDMA, and establishes the relation model between user capacity and multibeam pattern. Additionally, a novel particle swarm optimization (PSO) based on simulated annealing (SA) pattern synthesis method is proposed, which chooses user capacity as synthesis objective function. The numerical analysis, which is performed for a hexagonal array with 19 stacked patch elements, confirms that user capacity is at least doubled with the ``max-gain-flux'' beam coverage implemented by our method, compared to the ``iso-flux'' coverage when communication outage probability is 10%.
Minimum side-zone power to center-zone power ratio (MSCR) method is presented to estimate array errors of azimuth multichannel synthetic aperture radar (SAR). Spaceborne azimuth multichannel SAR is one of the most promising candidates for achieving high-resolution wide-swath imaging. However, array errors brought in by instrument influences and aperture position errors need to be compensated. MSCR method is designed to obtain phase error estimates by minimizing side-zone power to center-zone power ratio, where the side-zone and the center-zone indicate the intervals far from and around Doppler centroid respectively. The proposed method achieves significantly improved performance on phase error estimation especially when signal to noise ratio is low. Experiment results confirm the validity and solidity of the method.
A new analytical technique to study the complex resonances of a rectangular patch in a multilayered medium is introduced. The problem is formulated as an electric field integral equation (EFIE) in the spectral domain and discretized by means of products of Chebyshev polynomials of first and second kind multiplied by their orthogonal weights in a Galerkin's scheme. The method is fast convergent, i.e., few expansion functions are needed to achieve accurate results, but leads to the numerical evaluation of infinite double integrals of oscillating and slowly decaying functions. To overcome this problem, suitable half-space contributions are pulled out of the kernels of such integrals in order to obtain exponentially decaying integrands. Moreover, the slowly converging integrals of the extracted contributions are expressed as combinations of quickly converging integrals by means of algebraic manipulations and an appropriate integration procedure in the complex plane.
MIMO reference antennas are proposed for over the air (OTA) measurement applications. The reference antennas could get rid of feeding cable interference and control envelope correlation coefficients (ECC) continuously by only changing the length of an etched slot on a dual-feed PIFA. If only the ECC is investigated, the MIMO reference antenna is optimized to have a small variation of total efficiency from 70% to 50% when the ECC increases from 0.1 to 0.88. The prototypes are fabricated and measured in a scattered field chamber (SFC). Measurements agree well with the simulations. A practical example of applying this kind of reference antenna is provided. If the MIMO performance is studied, the MIMO reference antenna is proposed to own a large variation of total efficiencies from 90% to 47% while the ECC increases from 0 to 0.98. The bandwidth of the proposed reference antennas depend on the size of the antennas. This method is valid for all the frequencies.
This paper introduces a new numerical method to calculate the group delay, chromatic dispersion and dispersion slope of weakly-guiding optical fibers with arbitrary radial refractive index profiles. It is based on the analytic differentiation of the propagation coefficient up to the third order. The simulation results are compared to experimental data, with those calculated by other approaches and exact data where possible. Due to the analytical differentiation of the matrix equation, the method is more accurate compared to other approaches, it is also much faster than numerical differentiation as allows avoiding repeated solution of the eigenvalue problem to calculate the derivatives of the propagation coefficient. The precision of the method is limited only by the approximation errors of the mode solver. The Galerkin method with Laguerre-Gauss basis functions is used to determine the propagation coefficients of weakly-guiding structures. The new method enables fiber manufacturers to rapidly design dispersion characteristics of graded index, step index, single- and multiple-clad fibers, as well as few-mode and bend insensitive fibers.
The pattern synthesis for large antenna arrays has drawn significant attention because of its wide applications.This paper introduces a hybrid approach for the fast pencil beam pattern synthesis of the large non-uniform linear or planar array, which can significantly reduce the computational cost, the number of antenna in the array, the minimum sidelobe level and the null control.The proposed method has an iterative scheme which is composed of the nonuniform Fourier transform (NUFFT) and the global optimization method to minimize the peak sidelobe level and control the null. The NUFFT is utilized to determine excitation magnitudes for a fixed positions non-uniform array. The global optimization is used tofind the optimal postions lead thepeak sidelobe level minimum alternatively.The lower excitations can be deleted due to yielding less performance on sidelobe level, which is calledthe array removal strategy.Compare with conventional methods,the simulations on synthetic models show thata minimum sidelobe level and null control can be obtained in processing sparse linear and concentric circular antenna arrays more efficiently.
A Planar elliptic broadband antenna with reconfigurable dual stop-bands performance was successfully designed and performedfor multi-standard wireless communication systems. The proposed antenna consists of a broadband micro-strip fed printed monopole operating in the frequency range 0.75-6 GHz. The notch-band characteristic was obtained by printing two Open Loop Resonators (OLRs) on the front side of the substrate close to the micro-strip feed-line. By adjusting the OLRs parameters, mono or dual band-rejection can be obtained. The passive broadband antenna was optimized to achieve narrow band rejection over the UMTS-band (around 2.1 GHz) and the WiMAX-band (around 3.5 GHz). The agility was produced by loading a varactor diode on each OLR. The major advantages of this structure are the high selectivity of the dismissed-bands, continuous reconfiguration and wide tuning range of the notched bands. Four prototypes were realized and experimentally characterized. The measured tuning rangescorresponding to the notched bands are about 850 MHz (2.25-3.1 GHz) for the rejected UMTS-bandand 570 MHz (3.84-4.41 GHz) for the WiMAX-band. Simulated and measured resultsare presented and discussed.
Design, simulation, and measurement of a compact filtering microstrip antenna is presented. A coupled line, two hairpin resonators, and a rectangular patch are integrated to form the filtering antenna. The elements together function as a third order bandpass filter with Chebyshev equal ripple response of 0.043 dB at midband frequency of 2.0 GHz. The rectangular patch acts not only as a radiating element, but also as the last resonator of the bandpass filter. The proposed filtering antenna exhibits good out-of-band gain suppression, flat in-band gain response, good selectivity at the band edges, and well-shaped radiation pattern.
An innovative antenna on flexible substrate with two resonators is presented. The antenna is composed of a metallic wire sewn on the substrate. Two dipolar modes in far field are radiated. To understand the interaction of the resonators with the principal antenna, studies with and without the sleeves are done in near field and far field.
To eliminate the average reflectance of antireflection coatings to the greatest extent, a Genetic Programming (GP) algorithm is proposed to design and optimize the graded refractive index distribution profile for broadband omnidirectional antireflection coatings. The proposed GP-index profile in this paper can obtain an extremely low average reflectance of 4.61×10-7% over a wide range of incident angles and wavelengths which is obviously superior to the average reflectance of 8.09×10-3%, 3.29×10-4% and 4.35×10-5% for linear profile, cubic profile and quintic profile. That means, Fresnel reflection almost can be eliminated by the optimal GP-index profile for omnidirectional incidence over a broad wavelength range. Moreover, it is demonstrated the proposed GP-index profile has better robustness, and it still has the best broadband and omnidirectional antireflection characteristics for the TiO2/SiO2 graded-index AR coating. Therefore, the proposed GP-index profile is obviously superior to the conventional linear profile, cubic profile and quintic profile, and the design methodology presented in this paper that uses a genetic programming technique is a quite convenient means to pursue an optimal nonlinear refractive index profile with broadband and omnidirectional antireflection characteristics.
A two-strip narrow-frame monopole antenna for hepta-band WWAN/LTE smartphone applications is proposed. The brightest point of the proposed antenna is that its narrow edge has a width of only 5mm, which is very practical for current smartphone applications with larger touch-screens. In addition, the proposed narrow-frame antenna has a small volume of 60×5×5 mm3 and a simple structure, which comprises of a two-strip monopole loaded with a chip capacitor and an L-shape high-pass filter. Meanwhile, the propose antenna can cover the GSM850/900/1800/1900/UMTS2100/LTE2300/2500 bands. Finally, the operating principle of the proposed antenna is investigated and both simulated and measured results are presented and discussed.
In this paper, periodic structures are investigated in antenna design for wireless applications. These antennas were compared with CRLH miniaturization method. Three different models of patch antenna with coaxial feed on EBG ground, metamaterial substrate or EBG/AMC structure have been presented here. Also two compact dual-band antennas have been designed and fabricated based on CRLH techniques for wireless and GSM applications. The first antenna has directional pattern and operates at 1760, 2550 and 3850 MHz (three-band antenna) with gain 2.1, -3.9 and 2.5 dBi, and it is dual polarized. The size of prototype patch antenna is 20×20 mm2 which is reduced about %47 in comparison to conventional patch antenna at 2.5 GHz. The second antenna is designed by the use of interdigital capacitor and spiral inductor. Dimensions of antenna are 15.5×12 mm2, so the size is reduced about %69 in comparison to conventional microstrip patch antennas at 1.8 GHz. The second tri-band antenna operates at 1060 MHz, 1800 MHz and 2500 MHz in which two frequencies (1.8 and 2.5 GHz) are suitable for GMS and WLAN applications. Both structures have been designed and fabricated on FR4 low cost substrate with εr=4.4 and thickness of 1.6mm. All simulations are done with CST and HFSS. Equivalent circuit and experimental results are also presented and compared.
The major difficulty of realizing a micro-air-vehicle-borne (MAV-borne) synthetic aperture radar (SAR) is the motion errors that need to be precisely measured and compensated. This paper presents two novel motion measuring algorithms specifically for near-range applications. These algorithms use only low-cost micro-electronicmechanical system (MEMS) inertial measurement units (IMU). A MAV-borne SAR system was built equipped with a commercial off-the-shelf (COTS) motion sensing board. Several MAV-borne SAR measurements were performed for the first time in a hall with a realistic scene. SAR images were generated with proposed motion measuring algorithms in off-line mode. Obvious improvements in SAR image quality in terms of focusing have been observed after motion compensation with the proposed motion measuring algorithms. These results show that MAV-borne SAR together with low-cost IMU can yield very useful images.
Ground penetrating radar (GPR) has shown to provide useful results for detection of buried objects. However, its performance suffers from strong reflection from ground surface especially for shallowly buried targets. In such cases, the detection problem depends on the separation of the target signal from the ground backscatter such as landmines and unexploded ordnances. In this paper, we discuss and analyze the use of space-frequency time-reversal matrices for the enhancement of ground penetrating radar signals and potential clutter reduction. Through the use of sliding windows, submatrices from a given B-scan (radargram) are utilized to extract localized scattering information of a given detection scenario. Each sub-B-scan is decomposed to its singular vectors and later used to render synthetic aperture time-domain singular vector distributions corresponding to different scattering mechanisms. Later, they are weighted by the singular values and subtracted from the full B-scan to achieve reduced clutter and enhanced target response. The method shows satisfactory results for shallowly buried dielectric targets even in the presence of rough surface profiles.